0518a0bfc746bab4f257f2fa81ef7361f99ff113
[sfrench/cifs-2.6.git] / kernel / futex.c
1 /*
2  *  Fast Userspace Mutexes (which I call "Futexes!").
3  *  (C) Rusty Russell, IBM 2002
4  *
5  *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6  *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
7  *
8  *  Removed page pinning, fix privately mapped COW pages and other cleanups
9  *  (C) Copyright 2003, 2004 Jamie Lokier
10  *
11  *  Robust futex support started by Ingo Molnar
12  *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13  *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
14  *
15  *  PI-futex support started by Ingo Molnar and Thomas Gleixner
16  *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17  *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
18  *
19  *  PRIVATE futexes by Eric Dumazet
20  *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
21  *
22  *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23  *  Copyright (C) IBM Corporation, 2009
24  *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
25  *
26  *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27  *  enough at me, Linus for the original (flawed) idea, Matthew
28  *  Kirkwood for proof-of-concept implementation.
29  *
30  *  "The futexes are also cursed."
31  *  "But they come in a choice of three flavours!"
32  *
33  *  This program is free software; you can redistribute it and/or modify
34  *  it under the terms of the GNU General Public License as published by
35  *  the Free Software Foundation; either version 2 of the License, or
36  *  (at your option) any later version.
37  *
38  *  This program is distributed in the hope that it will be useful,
39  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
40  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
41  *  GNU General Public License for more details.
42  *
43  *  You should have received a copy of the GNU General Public License
44  *  along with this program; if not, write to the Free Software
45  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
46  */
47 #include <linux/slab.h>
48 #include <linux/poll.h>
49 #include <linux/fs.h>
50 #include <linux/file.h>
51 #include <linux/jhash.h>
52 #include <linux/init.h>
53 #include <linux/futex.h>
54 #include <linux/mount.h>
55 #include <linux/pagemap.h>
56 #include <linux/syscalls.h>
57 #include <linux/signal.h>
58 #include <linux/export.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
62 #include <linux/ptrace.h>
63 #include <linux/sched/rt.h>
64 #include <linux/sched/wake_q.h>
65 #include <linux/sched/mm.h>
66 #include <linux/hugetlb.h>
67 #include <linux/freezer.h>
68 #include <linux/bootmem.h>
69 #include <linux/fault-inject.h>
70
71 #include <asm/futex.h>
72
73 #include "locking/rtmutex_common.h"
74
75 /*
76  * READ this before attempting to hack on futexes!
77  *
78  * Basic futex operation and ordering guarantees
79  * =============================================
80  *
81  * The waiter reads the futex value in user space and calls
82  * futex_wait(). This function computes the hash bucket and acquires
83  * the hash bucket lock. After that it reads the futex user space value
84  * again and verifies that the data has not changed. If it has not changed
85  * it enqueues itself into the hash bucket, releases the hash bucket lock
86  * and schedules.
87  *
88  * The waker side modifies the user space value of the futex and calls
89  * futex_wake(). This function computes the hash bucket and acquires the
90  * hash bucket lock. Then it looks for waiters on that futex in the hash
91  * bucket and wakes them.
92  *
93  * In futex wake up scenarios where no tasks are blocked on a futex, taking
94  * the hb spinlock can be avoided and simply return. In order for this
95  * optimization to work, ordering guarantees must exist so that the waiter
96  * being added to the list is acknowledged when the list is concurrently being
97  * checked by the waker, avoiding scenarios like the following:
98  *
99  * CPU 0                               CPU 1
100  * val = *futex;
101  * sys_futex(WAIT, futex, val);
102  *   futex_wait(futex, val);
103  *   uval = *futex;
104  *                                     *futex = newval;
105  *                                     sys_futex(WAKE, futex);
106  *                                       futex_wake(futex);
107  *                                       if (queue_empty())
108  *                                         return;
109  *   if (uval == val)
110  *      lock(hash_bucket(futex));
111  *      queue();
112  *     unlock(hash_bucket(futex));
113  *     schedule();
114  *
115  * This would cause the waiter on CPU 0 to wait forever because it
116  * missed the transition of the user space value from val to newval
117  * and the waker did not find the waiter in the hash bucket queue.
118  *
119  * The correct serialization ensures that a waiter either observes
120  * the changed user space value before blocking or is woken by a
121  * concurrent waker:
122  *
123  * CPU 0                                 CPU 1
124  * val = *futex;
125  * sys_futex(WAIT, futex, val);
126  *   futex_wait(futex, val);
127  *
128  *   waiters++; (a)
129  *   smp_mb(); (A) <-- paired with -.
130  *                                  |
131  *   lock(hash_bucket(futex));      |
132  *                                  |
133  *   uval = *futex;                 |
134  *                                  |        *futex = newval;
135  *                                  |        sys_futex(WAKE, futex);
136  *                                  |          futex_wake(futex);
137  *                                  |
138  *                                  `--------> smp_mb(); (B)
139  *   if (uval == val)
140  *     queue();
141  *     unlock(hash_bucket(futex));
142  *     schedule();                         if (waiters)
143  *                                           lock(hash_bucket(futex));
144  *   else                                    wake_waiters(futex);
145  *     waiters--; (b)                        unlock(hash_bucket(futex));
146  *
147  * Where (A) orders the waiters increment and the futex value read through
148  * atomic operations (see hb_waiters_inc) and where (B) orders the write
149  * to futex and the waiters read -- this is done by the barriers for both
150  * shared and private futexes in get_futex_key_refs().
151  *
152  * This yields the following case (where X:=waiters, Y:=futex):
153  *
154  *      X = Y = 0
155  *
156  *      w[X]=1          w[Y]=1
157  *      MB              MB
158  *      r[Y]=y          r[X]=x
159  *
160  * Which guarantees that x==0 && y==0 is impossible; which translates back into
161  * the guarantee that we cannot both miss the futex variable change and the
162  * enqueue.
163  *
164  * Note that a new waiter is accounted for in (a) even when it is possible that
165  * the wait call can return error, in which case we backtrack from it in (b).
166  * Refer to the comment in queue_lock().
167  *
168  * Similarly, in order to account for waiters being requeued on another
169  * address we always increment the waiters for the destination bucket before
170  * acquiring the lock. It then decrements them again  after releasing it -
171  * the code that actually moves the futex(es) between hash buckets (requeue_futex)
172  * will do the additional required waiter count housekeeping. This is done for
173  * double_lock_hb() and double_unlock_hb(), respectively.
174  */
175
176 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
177 int __read_mostly futex_cmpxchg_enabled;
178 #endif
179
180 /*
181  * Futex flags used to encode options to functions and preserve them across
182  * restarts.
183  */
184 #ifdef CONFIG_MMU
185 # define FLAGS_SHARED           0x01
186 #else
187 /*
188  * NOMMU does not have per process address space. Let the compiler optimize
189  * code away.
190  */
191 # define FLAGS_SHARED           0x00
192 #endif
193 #define FLAGS_CLOCKRT           0x02
194 #define FLAGS_HAS_TIMEOUT       0x04
195
196 /*
197  * Priority Inheritance state:
198  */
199 struct futex_pi_state {
200         /*
201          * list of 'owned' pi_state instances - these have to be
202          * cleaned up in do_exit() if the task exits prematurely:
203          */
204         struct list_head list;
205
206         /*
207          * The PI object:
208          */
209         struct rt_mutex pi_mutex;
210
211         struct task_struct *owner;
212         atomic_t refcount;
213
214         union futex_key key;
215 } __randomize_layout;
216
217 /**
218  * struct futex_q - The hashed futex queue entry, one per waiting task
219  * @list:               priority-sorted list of tasks waiting on this futex
220  * @task:               the task waiting on the futex
221  * @lock_ptr:           the hash bucket lock
222  * @key:                the key the futex is hashed on
223  * @pi_state:           optional priority inheritance state
224  * @rt_waiter:          rt_waiter storage for use with requeue_pi
225  * @requeue_pi_key:     the requeue_pi target futex key
226  * @bitset:             bitset for the optional bitmasked wakeup
227  *
228  * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
229  * we can wake only the relevant ones (hashed queues may be shared).
230  *
231  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
232  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
233  * The order of wakeup is always to make the first condition true, then
234  * the second.
235  *
236  * PI futexes are typically woken before they are removed from the hash list via
237  * the rt_mutex code. See unqueue_me_pi().
238  */
239 struct futex_q {
240         struct plist_node list;
241
242         struct task_struct *task;
243         spinlock_t *lock_ptr;
244         union futex_key key;
245         struct futex_pi_state *pi_state;
246         struct rt_mutex_waiter *rt_waiter;
247         union futex_key *requeue_pi_key;
248         u32 bitset;
249 } __randomize_layout;
250
251 static const struct futex_q futex_q_init = {
252         /* list gets initialized in queue_me()*/
253         .key = FUTEX_KEY_INIT,
254         .bitset = FUTEX_BITSET_MATCH_ANY
255 };
256
257 /*
258  * Hash buckets are shared by all the futex_keys that hash to the same
259  * location.  Each key may have multiple futex_q structures, one for each task
260  * waiting on a futex.
261  */
262 struct futex_hash_bucket {
263         atomic_t waiters;
264         spinlock_t lock;
265         struct plist_head chain;
266 } ____cacheline_aligned_in_smp;
267
268 /*
269  * The base of the bucket array and its size are always used together
270  * (after initialization only in hash_futex()), so ensure that they
271  * reside in the same cacheline.
272  */
273 static struct {
274         struct futex_hash_bucket *queues;
275         unsigned long            hashsize;
276 } __futex_data __read_mostly __aligned(2*sizeof(long));
277 #define futex_queues   (__futex_data.queues)
278 #define futex_hashsize (__futex_data.hashsize)
279
280
281 /*
282  * Fault injections for futexes.
283  */
284 #ifdef CONFIG_FAIL_FUTEX
285
286 static struct {
287         struct fault_attr attr;
288
289         bool ignore_private;
290 } fail_futex = {
291         .attr = FAULT_ATTR_INITIALIZER,
292         .ignore_private = false,
293 };
294
295 static int __init setup_fail_futex(char *str)
296 {
297         return setup_fault_attr(&fail_futex.attr, str);
298 }
299 __setup("fail_futex=", setup_fail_futex);
300
301 static bool should_fail_futex(bool fshared)
302 {
303         if (fail_futex.ignore_private && !fshared)
304                 return false;
305
306         return should_fail(&fail_futex.attr, 1);
307 }
308
309 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
310
311 static int __init fail_futex_debugfs(void)
312 {
313         umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
314         struct dentry *dir;
315
316         dir = fault_create_debugfs_attr("fail_futex", NULL,
317                                         &fail_futex.attr);
318         if (IS_ERR(dir))
319                 return PTR_ERR(dir);
320
321         if (!debugfs_create_bool("ignore-private", mode, dir,
322                                  &fail_futex.ignore_private)) {
323                 debugfs_remove_recursive(dir);
324                 return -ENOMEM;
325         }
326
327         return 0;
328 }
329
330 late_initcall(fail_futex_debugfs);
331
332 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
333
334 #else
335 static inline bool should_fail_futex(bool fshared)
336 {
337         return false;
338 }
339 #endif /* CONFIG_FAIL_FUTEX */
340
341 static inline void futex_get_mm(union futex_key *key)
342 {
343         mmgrab(key->private.mm);
344         /*
345          * Ensure futex_get_mm() implies a full barrier such that
346          * get_futex_key() implies a full barrier. This is relied upon
347          * as smp_mb(); (B), see the ordering comment above.
348          */
349         smp_mb__after_atomic();
350 }
351
352 /*
353  * Reflects a new waiter being added to the waitqueue.
354  */
355 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
356 {
357 #ifdef CONFIG_SMP
358         atomic_inc(&hb->waiters);
359         /*
360          * Full barrier (A), see the ordering comment above.
361          */
362         smp_mb__after_atomic();
363 #endif
364 }
365
366 /*
367  * Reflects a waiter being removed from the waitqueue by wakeup
368  * paths.
369  */
370 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
371 {
372 #ifdef CONFIG_SMP
373         atomic_dec(&hb->waiters);
374 #endif
375 }
376
377 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
378 {
379 #ifdef CONFIG_SMP
380         return atomic_read(&hb->waiters);
381 #else
382         return 1;
383 #endif
384 }
385
386 /**
387  * hash_futex - Return the hash bucket in the global hash
388  * @key:        Pointer to the futex key for which the hash is calculated
389  *
390  * We hash on the keys returned from get_futex_key (see below) and return the
391  * corresponding hash bucket in the global hash.
392  */
393 static struct futex_hash_bucket *hash_futex(union futex_key *key)
394 {
395         u32 hash = jhash2((u32*)&key->both.word,
396                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
397                           key->both.offset);
398         return &futex_queues[hash & (futex_hashsize - 1)];
399 }
400
401
402 /**
403  * match_futex - Check whether two futex keys are equal
404  * @key1:       Pointer to key1
405  * @key2:       Pointer to key2
406  *
407  * Return 1 if two futex_keys are equal, 0 otherwise.
408  */
409 static inline int match_futex(union futex_key *key1, union futex_key *key2)
410 {
411         return (key1 && key2
412                 && key1->both.word == key2->both.word
413                 && key1->both.ptr == key2->both.ptr
414                 && key1->both.offset == key2->both.offset);
415 }
416
417 /*
418  * Take a reference to the resource addressed by a key.
419  * Can be called while holding spinlocks.
420  *
421  */
422 static void get_futex_key_refs(union futex_key *key)
423 {
424         if (!key->both.ptr)
425                 return;
426
427         /*
428          * On MMU less systems futexes are always "private" as there is no per
429          * process address space. We need the smp wmb nevertheless - yes,
430          * arch/blackfin has MMU less SMP ...
431          */
432         if (!IS_ENABLED(CONFIG_MMU)) {
433                 smp_mb(); /* explicit smp_mb(); (B) */
434                 return;
435         }
436
437         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
438         case FUT_OFF_INODE:
439                 ihold(key->shared.inode); /* implies smp_mb(); (B) */
440                 break;
441         case FUT_OFF_MMSHARED:
442                 futex_get_mm(key); /* implies smp_mb(); (B) */
443                 break;
444         default:
445                 /*
446                  * Private futexes do not hold reference on an inode or
447                  * mm, therefore the only purpose of calling get_futex_key_refs
448                  * is because we need the barrier for the lockless waiter check.
449                  */
450                 smp_mb(); /* explicit smp_mb(); (B) */
451         }
452 }
453
454 /*
455  * Drop a reference to the resource addressed by a key.
456  * The hash bucket spinlock must not be held. This is
457  * a no-op for private futexes, see comment in the get
458  * counterpart.
459  */
460 static void drop_futex_key_refs(union futex_key *key)
461 {
462         if (!key->both.ptr) {
463                 /* If we're here then we tried to put a key we failed to get */
464                 WARN_ON_ONCE(1);
465                 return;
466         }
467
468         if (!IS_ENABLED(CONFIG_MMU))
469                 return;
470
471         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
472         case FUT_OFF_INODE:
473                 iput(key->shared.inode);
474                 break;
475         case FUT_OFF_MMSHARED:
476                 mmdrop(key->private.mm);
477                 break;
478         }
479 }
480
481 /**
482  * get_futex_key() - Get parameters which are the keys for a futex
483  * @uaddr:      virtual address of the futex
484  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
485  * @key:        address where result is stored.
486  * @rw:         mapping needs to be read/write (values: VERIFY_READ,
487  *              VERIFY_WRITE)
488  *
489  * Return: a negative error code or 0
490  *
491  * The key words are stored in @key on success.
492  *
493  * For shared mappings, it's (page->index, file_inode(vma->vm_file),
494  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
495  * We can usually work out the index without swapping in the page.
496  *
497  * lock_page() might sleep, the caller should not hold a spinlock.
498  */
499 static int
500 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
501 {
502         unsigned long address = (unsigned long)uaddr;
503         struct mm_struct *mm = current->mm;
504         struct page *page, *tail;
505         struct address_space *mapping;
506         int err, ro = 0;
507
508         /*
509          * The futex address must be "naturally" aligned.
510          */
511         key->both.offset = address % PAGE_SIZE;
512         if (unlikely((address % sizeof(u32)) != 0))
513                 return -EINVAL;
514         address -= key->both.offset;
515
516         if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
517                 return -EFAULT;
518
519         if (unlikely(should_fail_futex(fshared)))
520                 return -EFAULT;
521
522         /*
523          * PROCESS_PRIVATE futexes are fast.
524          * As the mm cannot disappear under us and the 'key' only needs
525          * virtual address, we dont even have to find the underlying vma.
526          * Note : We do have to check 'uaddr' is a valid user address,
527          *        but access_ok() should be faster than find_vma()
528          */
529         if (!fshared) {
530                 key->private.mm = mm;
531                 key->private.address = address;
532                 get_futex_key_refs(key);  /* implies smp_mb(); (B) */
533                 return 0;
534         }
535
536 again:
537         /* Ignore any VERIFY_READ mapping (futex common case) */
538         if (unlikely(should_fail_futex(fshared)))
539                 return -EFAULT;
540
541         err = get_user_pages_fast(address, 1, 1, &page);
542         /*
543          * If write access is not required (eg. FUTEX_WAIT), try
544          * and get read-only access.
545          */
546         if (err == -EFAULT && rw == VERIFY_READ) {
547                 err = get_user_pages_fast(address, 1, 0, &page);
548                 ro = 1;
549         }
550         if (err < 0)
551                 return err;
552         else
553                 err = 0;
554
555         /*
556          * The treatment of mapping from this point on is critical. The page
557          * lock protects many things but in this context the page lock
558          * stabilizes mapping, prevents inode freeing in the shared
559          * file-backed region case and guards against movement to swap cache.
560          *
561          * Strictly speaking the page lock is not needed in all cases being
562          * considered here and page lock forces unnecessarily serialization
563          * From this point on, mapping will be re-verified if necessary and
564          * page lock will be acquired only if it is unavoidable
565          *
566          * Mapping checks require the head page for any compound page so the
567          * head page and mapping is looked up now. For anonymous pages, it
568          * does not matter if the page splits in the future as the key is
569          * based on the address. For filesystem-backed pages, the tail is
570          * required as the index of the page determines the key. For
571          * base pages, there is no tail page and tail == page.
572          */
573         tail = page;
574         page = compound_head(page);
575         mapping = READ_ONCE(page->mapping);
576
577         /*
578          * If page->mapping is NULL, then it cannot be a PageAnon
579          * page; but it might be the ZERO_PAGE or in the gate area or
580          * in a special mapping (all cases which we are happy to fail);
581          * or it may have been a good file page when get_user_pages_fast
582          * found it, but truncated or holepunched or subjected to
583          * invalidate_complete_page2 before we got the page lock (also
584          * cases which we are happy to fail).  And we hold a reference,
585          * so refcount care in invalidate_complete_page's remove_mapping
586          * prevents drop_caches from setting mapping to NULL beneath us.
587          *
588          * The case we do have to guard against is when memory pressure made
589          * shmem_writepage move it from filecache to swapcache beneath us:
590          * an unlikely race, but we do need to retry for page->mapping.
591          */
592         if (unlikely(!mapping)) {
593                 int shmem_swizzled;
594
595                 /*
596                  * Page lock is required to identify which special case above
597                  * applies. If this is really a shmem page then the page lock
598                  * will prevent unexpected transitions.
599                  */
600                 lock_page(page);
601                 shmem_swizzled = PageSwapCache(page) || page->mapping;
602                 unlock_page(page);
603                 put_page(page);
604
605                 if (shmem_swizzled)
606                         goto again;
607
608                 return -EFAULT;
609         }
610
611         /*
612          * Private mappings are handled in a simple way.
613          *
614          * If the futex key is stored on an anonymous page, then the associated
615          * object is the mm which is implicitly pinned by the calling process.
616          *
617          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
618          * it's a read-only handle, it's expected that futexes attach to
619          * the object not the particular process.
620          */
621         if (PageAnon(page)) {
622                 /*
623                  * A RO anonymous page will never change and thus doesn't make
624                  * sense for futex operations.
625                  */
626                 if (unlikely(should_fail_futex(fshared)) || ro) {
627                         err = -EFAULT;
628                         goto out;
629                 }
630
631                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
632                 key->private.mm = mm;
633                 key->private.address = address;
634
635                 get_futex_key_refs(key); /* implies smp_mb(); (B) */
636
637         } else {
638                 struct inode *inode;
639
640                 /*
641                  * The associated futex object in this case is the inode and
642                  * the page->mapping must be traversed. Ordinarily this should
643                  * be stabilised under page lock but it's not strictly
644                  * necessary in this case as we just want to pin the inode, not
645                  * update the radix tree or anything like that.
646                  *
647                  * The RCU read lock is taken as the inode is finally freed
648                  * under RCU. If the mapping still matches expectations then the
649                  * mapping->host can be safely accessed as being a valid inode.
650                  */
651                 rcu_read_lock();
652
653                 if (READ_ONCE(page->mapping) != mapping) {
654                         rcu_read_unlock();
655                         put_page(page);
656
657                         goto again;
658                 }
659
660                 inode = READ_ONCE(mapping->host);
661                 if (!inode) {
662                         rcu_read_unlock();
663                         put_page(page);
664
665                         goto again;
666                 }
667
668                 /*
669                  * Take a reference unless it is about to be freed. Previously
670                  * this reference was taken by ihold under the page lock
671                  * pinning the inode in place so i_lock was unnecessary. The
672                  * only way for this check to fail is if the inode was
673                  * truncated in parallel which is almost certainly an
674                  * application bug. In such a case, just retry.
675                  *
676                  * We are not calling into get_futex_key_refs() in file-backed
677                  * cases, therefore a successful atomic_inc return below will
678                  * guarantee that get_futex_key() will still imply smp_mb(); (B).
679                  */
680                 if (!atomic_inc_not_zero(&inode->i_count)) {
681                         rcu_read_unlock();
682                         put_page(page);
683
684                         goto again;
685                 }
686
687                 /* Should be impossible but lets be paranoid for now */
688                 if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
689                         err = -EFAULT;
690                         rcu_read_unlock();
691                         iput(inode);
692
693                         goto out;
694                 }
695
696                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
697                 key->shared.inode = inode;
698                 key->shared.pgoff = basepage_index(tail);
699                 rcu_read_unlock();
700         }
701
702 out:
703         put_page(page);
704         return err;
705 }
706
707 static inline void put_futex_key(union futex_key *key)
708 {
709         drop_futex_key_refs(key);
710 }
711
712 /**
713  * fault_in_user_writeable() - Fault in user address and verify RW access
714  * @uaddr:      pointer to faulting user space address
715  *
716  * Slow path to fixup the fault we just took in the atomic write
717  * access to @uaddr.
718  *
719  * We have no generic implementation of a non-destructive write to the
720  * user address. We know that we faulted in the atomic pagefault
721  * disabled section so we can as well avoid the #PF overhead by
722  * calling get_user_pages() right away.
723  */
724 static int fault_in_user_writeable(u32 __user *uaddr)
725 {
726         struct mm_struct *mm = current->mm;
727         int ret;
728
729         down_read(&mm->mmap_sem);
730         ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
731                                FAULT_FLAG_WRITE, NULL);
732         up_read(&mm->mmap_sem);
733
734         return ret < 0 ? ret : 0;
735 }
736
737 /**
738  * futex_top_waiter() - Return the highest priority waiter on a futex
739  * @hb:         the hash bucket the futex_q's reside in
740  * @key:        the futex key (to distinguish it from other futex futex_q's)
741  *
742  * Must be called with the hb lock held.
743  */
744 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
745                                         union futex_key *key)
746 {
747         struct futex_q *this;
748
749         plist_for_each_entry(this, &hb->chain, list) {
750                 if (match_futex(&this->key, key))
751                         return this;
752         }
753         return NULL;
754 }
755
756 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
757                                       u32 uval, u32 newval)
758 {
759         int ret;
760
761         pagefault_disable();
762         ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
763         pagefault_enable();
764
765         return ret;
766 }
767
768 static int get_futex_value_locked(u32 *dest, u32 __user *from)
769 {
770         int ret;
771
772         pagefault_disable();
773         ret = __get_user(*dest, from);
774         pagefault_enable();
775
776         return ret ? -EFAULT : 0;
777 }
778
779
780 /*
781  * PI code:
782  */
783 static int refill_pi_state_cache(void)
784 {
785         struct futex_pi_state *pi_state;
786
787         if (likely(current->pi_state_cache))
788                 return 0;
789
790         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
791
792         if (!pi_state)
793                 return -ENOMEM;
794
795         INIT_LIST_HEAD(&pi_state->list);
796         /* pi_mutex gets initialized later */
797         pi_state->owner = NULL;
798         atomic_set(&pi_state->refcount, 1);
799         pi_state->key = FUTEX_KEY_INIT;
800
801         current->pi_state_cache = pi_state;
802
803         return 0;
804 }
805
806 static struct futex_pi_state *alloc_pi_state(void)
807 {
808         struct futex_pi_state *pi_state = current->pi_state_cache;
809
810         WARN_ON(!pi_state);
811         current->pi_state_cache = NULL;
812
813         return pi_state;
814 }
815
816 static void get_pi_state(struct futex_pi_state *pi_state)
817 {
818         WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
819 }
820
821 /*
822  * Drops a reference to the pi_state object and frees or caches it
823  * when the last reference is gone.
824  */
825 static void put_pi_state(struct futex_pi_state *pi_state)
826 {
827         if (!pi_state)
828                 return;
829
830         if (!atomic_dec_and_test(&pi_state->refcount))
831                 return;
832
833         /*
834          * If pi_state->owner is NULL, the owner is most probably dying
835          * and has cleaned up the pi_state already
836          */
837         if (pi_state->owner) {
838                 struct task_struct *owner;
839
840                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
841                 owner = pi_state->owner;
842                 if (owner) {
843                         raw_spin_lock(&owner->pi_lock);
844                         list_del_init(&pi_state->list);
845                         raw_spin_unlock(&owner->pi_lock);
846                 }
847                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
848                 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
849         }
850
851         if (current->pi_state_cache) {
852                 kfree(pi_state);
853         } else {
854                 /*
855                  * pi_state->list is already empty.
856                  * clear pi_state->owner.
857                  * refcount is at 0 - put it back to 1.
858                  */
859                 pi_state->owner = NULL;
860                 atomic_set(&pi_state->refcount, 1);
861                 current->pi_state_cache = pi_state;
862         }
863 }
864
865 /*
866  * Look up the task based on what TID userspace gave us.
867  * We dont trust it.
868  */
869 static struct task_struct *futex_find_get_task(pid_t pid)
870 {
871         struct task_struct *p;
872
873         rcu_read_lock();
874         p = find_task_by_vpid(pid);
875         if (p)
876                 get_task_struct(p);
877
878         rcu_read_unlock();
879
880         return p;
881 }
882
883 #ifdef CONFIG_FUTEX_PI
884
885 /*
886  * This task is holding PI mutexes at exit time => bad.
887  * Kernel cleans up PI-state, but userspace is likely hosed.
888  * (Robust-futex cleanup is separate and might save the day for userspace.)
889  */
890 void exit_pi_state_list(struct task_struct *curr)
891 {
892         struct list_head *next, *head = &curr->pi_state_list;
893         struct futex_pi_state *pi_state;
894         struct futex_hash_bucket *hb;
895         union futex_key key = FUTEX_KEY_INIT;
896
897         if (!futex_cmpxchg_enabled)
898                 return;
899         /*
900          * We are a ZOMBIE and nobody can enqueue itself on
901          * pi_state_list anymore, but we have to be careful
902          * versus waiters unqueueing themselves:
903          */
904         raw_spin_lock_irq(&curr->pi_lock);
905         while (!list_empty(head)) {
906
907                 next = head->next;
908                 pi_state = list_entry(next, struct futex_pi_state, list);
909                 key = pi_state->key;
910                 hb = hash_futex(&key);
911                 raw_spin_unlock_irq(&curr->pi_lock);
912
913                 spin_lock(&hb->lock);
914                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
915                 raw_spin_lock(&curr->pi_lock);
916                 /*
917                  * We dropped the pi-lock, so re-check whether this
918                  * task still owns the PI-state:
919                  */
920                 if (head->next != next) {
921                         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
922                         spin_unlock(&hb->lock);
923                         continue;
924                 }
925
926                 WARN_ON(pi_state->owner != curr);
927                 WARN_ON(list_empty(&pi_state->list));
928                 list_del_init(&pi_state->list);
929                 pi_state->owner = NULL;
930                 raw_spin_unlock(&curr->pi_lock);
931
932                 get_pi_state(pi_state);
933                 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
934                 spin_unlock(&hb->lock);
935
936                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
937                 put_pi_state(pi_state);
938
939                 raw_spin_lock_irq(&curr->pi_lock);
940         }
941         raw_spin_unlock_irq(&curr->pi_lock);
942 }
943
944 #endif
945
946 /*
947  * We need to check the following states:
948  *
949  *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
950  *
951  * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
952  * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
953  *
954  * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
955  *
956  * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
957  * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
958  *
959  * [6]  Found  | Found    | task      | 0         | 1      | Valid
960  *
961  * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
962  *
963  * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
964  * [9]  Found  | Found    | task      | 0         | 0      | Invalid
965  * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
966  *
967  * [1]  Indicates that the kernel can acquire the futex atomically. We
968  *      came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
969  *
970  * [2]  Valid, if TID does not belong to a kernel thread. If no matching
971  *      thread is found then it indicates that the owner TID has died.
972  *
973  * [3]  Invalid. The waiter is queued on a non PI futex
974  *
975  * [4]  Valid state after exit_robust_list(), which sets the user space
976  *      value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
977  *
978  * [5]  The user space value got manipulated between exit_robust_list()
979  *      and exit_pi_state_list()
980  *
981  * [6]  Valid state after exit_pi_state_list() which sets the new owner in
982  *      the pi_state but cannot access the user space value.
983  *
984  * [7]  pi_state->owner can only be NULL when the OWNER_DIED bit is set.
985  *
986  * [8]  Owner and user space value match
987  *
988  * [9]  There is no transient state which sets the user space TID to 0
989  *      except exit_robust_list(), but this is indicated by the
990  *      FUTEX_OWNER_DIED bit. See [4]
991  *
992  * [10] There is no transient state which leaves owner and user space
993  *      TID out of sync.
994  *
995  *
996  * Serialization and lifetime rules:
997  *
998  * hb->lock:
999  *
1000  *      hb -> futex_q, relation
1001  *      futex_q -> pi_state, relation
1002  *
1003  *      (cannot be raw because hb can contain arbitrary amount
1004  *       of futex_q's)
1005  *
1006  * pi_mutex->wait_lock:
1007  *
1008  *      {uval, pi_state}
1009  *
1010  *      (and pi_mutex 'obviously')
1011  *
1012  * p->pi_lock:
1013  *
1014  *      p->pi_state_list -> pi_state->list, relation
1015  *
1016  * pi_state->refcount:
1017  *
1018  *      pi_state lifetime
1019  *
1020  *
1021  * Lock order:
1022  *
1023  *   hb->lock
1024  *     pi_mutex->wait_lock
1025  *       p->pi_lock
1026  *
1027  */
1028
1029 /*
1030  * Validate that the existing waiter has a pi_state and sanity check
1031  * the pi_state against the user space value. If correct, attach to
1032  * it.
1033  */
1034 static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
1035                               struct futex_pi_state *pi_state,
1036                               struct futex_pi_state **ps)
1037 {
1038         pid_t pid = uval & FUTEX_TID_MASK;
1039         u32 uval2;
1040         int ret;
1041
1042         /*
1043          * Userspace might have messed up non-PI and PI futexes [3]
1044          */
1045         if (unlikely(!pi_state))
1046                 return -EINVAL;
1047
1048         /*
1049          * We get here with hb->lock held, and having found a
1050          * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
1051          * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
1052          * which in turn means that futex_lock_pi() still has a reference on
1053          * our pi_state.
1054          *
1055          * The waiter holding a reference on @pi_state also protects against
1056          * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
1057          * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
1058          * free pi_state before we can take a reference ourselves.
1059          */
1060         WARN_ON(!atomic_read(&pi_state->refcount));
1061
1062         /*
1063          * Now that we have a pi_state, we can acquire wait_lock
1064          * and do the state validation.
1065          */
1066         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1067
1068         /*
1069          * Since {uval, pi_state} is serialized by wait_lock, and our current
1070          * uval was read without holding it, it can have changed. Verify it
1071          * still is what we expect it to be, otherwise retry the entire
1072          * operation.
1073          */
1074         if (get_futex_value_locked(&uval2, uaddr))
1075                 goto out_efault;
1076
1077         if (uval != uval2)
1078                 goto out_eagain;
1079
1080         /*
1081          * Handle the owner died case:
1082          */
1083         if (uval & FUTEX_OWNER_DIED) {
1084                 /*
1085                  * exit_pi_state_list sets owner to NULL and wakes the
1086                  * topmost waiter. The task which acquires the
1087                  * pi_state->rt_mutex will fixup owner.
1088                  */
1089                 if (!pi_state->owner) {
1090                         /*
1091                          * No pi state owner, but the user space TID
1092                          * is not 0. Inconsistent state. [5]
1093                          */
1094                         if (pid)
1095                                 goto out_einval;
1096                         /*
1097                          * Take a ref on the state and return success. [4]
1098                          */
1099                         goto out_attach;
1100                 }
1101
1102                 /*
1103                  * If TID is 0, then either the dying owner has not
1104                  * yet executed exit_pi_state_list() or some waiter
1105                  * acquired the rtmutex in the pi state, but did not
1106                  * yet fixup the TID in user space.
1107                  *
1108                  * Take a ref on the state and return success. [6]
1109                  */
1110                 if (!pid)
1111                         goto out_attach;
1112         } else {
1113                 /*
1114                  * If the owner died bit is not set, then the pi_state
1115                  * must have an owner. [7]
1116                  */
1117                 if (!pi_state->owner)
1118                         goto out_einval;
1119         }
1120
1121         /*
1122          * Bail out if user space manipulated the futex value. If pi
1123          * state exists then the owner TID must be the same as the
1124          * user space TID. [9/10]
1125          */
1126         if (pid != task_pid_vnr(pi_state->owner))
1127                 goto out_einval;
1128
1129 out_attach:
1130         get_pi_state(pi_state);
1131         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1132         *ps = pi_state;
1133         return 0;
1134
1135 out_einval:
1136         ret = -EINVAL;
1137         goto out_error;
1138
1139 out_eagain:
1140         ret = -EAGAIN;
1141         goto out_error;
1142
1143 out_efault:
1144         ret = -EFAULT;
1145         goto out_error;
1146
1147 out_error:
1148         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1149         return ret;
1150 }
1151
1152 /*
1153  * Lookup the task for the TID provided from user space and attach to
1154  * it after doing proper sanity checks.
1155  */
1156 static int attach_to_pi_owner(u32 uval, union futex_key *key,
1157                               struct futex_pi_state **ps)
1158 {
1159         pid_t pid = uval & FUTEX_TID_MASK;
1160         struct futex_pi_state *pi_state;
1161         struct task_struct *p;
1162
1163         /*
1164          * We are the first waiter - try to look up the real owner and attach
1165          * the new pi_state to it, but bail out when TID = 0 [1]
1166          */
1167         if (!pid)
1168                 return -ESRCH;
1169         p = futex_find_get_task(pid);
1170         if (!p)
1171                 return -ESRCH;
1172
1173         if (unlikely(p->flags & PF_KTHREAD)) {
1174                 put_task_struct(p);
1175                 return -EPERM;
1176         }
1177
1178         /*
1179          * We need to look at the task state flags to figure out,
1180          * whether the task is exiting. To protect against the do_exit
1181          * change of the task flags, we do this protected by
1182          * p->pi_lock:
1183          */
1184         raw_spin_lock_irq(&p->pi_lock);
1185         if (unlikely(p->flags & PF_EXITING)) {
1186                 /*
1187                  * The task is on the way out. When PF_EXITPIDONE is
1188                  * set, we know that the task has finished the
1189                  * cleanup:
1190                  */
1191                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
1192
1193                 raw_spin_unlock_irq(&p->pi_lock);
1194                 put_task_struct(p);
1195                 return ret;
1196         }
1197
1198         /*
1199          * No existing pi state. First waiter. [2]
1200          *
1201          * This creates pi_state, we have hb->lock held, this means nothing can
1202          * observe this state, wait_lock is irrelevant.
1203          */
1204         pi_state = alloc_pi_state();
1205
1206         /*
1207          * Initialize the pi_mutex in locked state and make @p
1208          * the owner of it:
1209          */
1210         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1211
1212         /* Store the key for possible exit cleanups: */
1213         pi_state->key = *key;
1214
1215         WARN_ON(!list_empty(&pi_state->list));
1216         list_add(&pi_state->list, &p->pi_state_list);
1217         /*
1218          * Assignment without holding pi_state->pi_mutex.wait_lock is safe
1219          * because there is no concurrency as the object is not published yet.
1220          */
1221         pi_state->owner = p;
1222         raw_spin_unlock_irq(&p->pi_lock);
1223
1224         put_task_struct(p);
1225
1226         *ps = pi_state;
1227
1228         return 0;
1229 }
1230
1231 static int lookup_pi_state(u32 __user *uaddr, u32 uval,
1232                            struct futex_hash_bucket *hb,
1233                            union futex_key *key, struct futex_pi_state **ps)
1234 {
1235         struct futex_q *top_waiter = futex_top_waiter(hb, key);
1236
1237         /*
1238          * If there is a waiter on that futex, validate it and
1239          * attach to the pi_state when the validation succeeds.
1240          */
1241         if (top_waiter)
1242                 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1243
1244         /*
1245          * We are the first waiter - try to look up the owner based on
1246          * @uval and attach to it.
1247          */
1248         return attach_to_pi_owner(uval, key, ps);
1249 }
1250
1251 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1252 {
1253         u32 uninitialized_var(curval);
1254
1255         if (unlikely(should_fail_futex(true)))
1256                 return -EFAULT;
1257
1258         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1259                 return -EFAULT;
1260
1261         /* If user space value changed, let the caller retry */
1262         return curval != uval ? -EAGAIN : 0;
1263 }
1264
1265 /**
1266  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1267  * @uaddr:              the pi futex user address
1268  * @hb:                 the pi futex hash bucket
1269  * @key:                the futex key associated with uaddr and hb
1270  * @ps:                 the pi_state pointer where we store the result of the
1271  *                      lookup
1272  * @task:               the task to perform the atomic lock work for.  This will
1273  *                      be "current" except in the case of requeue pi.
1274  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1275  *
1276  * Return:
1277  *  -  0 - ready to wait;
1278  *  -  1 - acquired the lock;
1279  *  - <0 - error
1280  *
1281  * The hb->lock and futex_key refs shall be held by the caller.
1282  */
1283 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1284                                 union futex_key *key,
1285                                 struct futex_pi_state **ps,
1286                                 struct task_struct *task, int set_waiters)
1287 {
1288         u32 uval, newval, vpid = task_pid_vnr(task);
1289         struct futex_q *top_waiter;
1290         int ret;
1291
1292         /*
1293          * Read the user space value first so we can validate a few
1294          * things before proceeding further.
1295          */
1296         if (get_futex_value_locked(&uval, uaddr))
1297                 return -EFAULT;
1298
1299         if (unlikely(should_fail_futex(true)))
1300                 return -EFAULT;
1301
1302         /*
1303          * Detect deadlocks.
1304          */
1305         if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1306                 return -EDEADLK;
1307
1308         if ((unlikely(should_fail_futex(true))))
1309                 return -EDEADLK;
1310
1311         /*
1312          * Lookup existing state first. If it exists, try to attach to
1313          * its pi_state.
1314          */
1315         top_waiter = futex_top_waiter(hb, key);
1316         if (top_waiter)
1317                 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1318
1319         /*
1320          * No waiter and user TID is 0. We are here because the
1321          * waiters or the owner died bit is set or called from
1322          * requeue_cmp_pi or for whatever reason something took the
1323          * syscall.
1324          */
1325         if (!(uval & FUTEX_TID_MASK)) {
1326                 /*
1327                  * We take over the futex. No other waiters and the user space
1328                  * TID is 0. We preserve the owner died bit.
1329                  */
1330                 newval = uval & FUTEX_OWNER_DIED;
1331                 newval |= vpid;
1332
1333                 /* The futex requeue_pi code can enforce the waiters bit */
1334                 if (set_waiters)
1335                         newval |= FUTEX_WAITERS;
1336
1337                 ret = lock_pi_update_atomic(uaddr, uval, newval);
1338                 /* If the take over worked, return 1 */
1339                 return ret < 0 ? ret : 1;
1340         }
1341
1342         /*
1343          * First waiter. Set the waiters bit before attaching ourself to
1344          * the owner. If owner tries to unlock, it will be forced into
1345          * the kernel and blocked on hb->lock.
1346          */
1347         newval = uval | FUTEX_WAITERS;
1348         ret = lock_pi_update_atomic(uaddr, uval, newval);
1349         if (ret)
1350                 return ret;
1351         /*
1352          * If the update of the user space value succeeded, we try to
1353          * attach to the owner. If that fails, no harm done, we only
1354          * set the FUTEX_WAITERS bit in the user space variable.
1355          */
1356         return attach_to_pi_owner(uval, key, ps);
1357 }
1358
1359 /**
1360  * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1361  * @q:  The futex_q to unqueue
1362  *
1363  * The q->lock_ptr must not be NULL and must be held by the caller.
1364  */
1365 static void __unqueue_futex(struct futex_q *q)
1366 {
1367         struct futex_hash_bucket *hb;
1368
1369         if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1370             || WARN_ON(plist_node_empty(&q->list)))
1371                 return;
1372
1373         hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1374         plist_del(&q->list, &hb->chain);
1375         hb_waiters_dec(hb);
1376 }
1377
1378 /*
1379  * The hash bucket lock must be held when this is called.
1380  * Afterwards, the futex_q must not be accessed. Callers
1381  * must ensure to later call wake_up_q() for the actual
1382  * wakeups to occur.
1383  */
1384 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1385 {
1386         struct task_struct *p = q->task;
1387
1388         if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1389                 return;
1390
1391         /*
1392          * Queue the task for later wakeup for after we've released
1393          * the hb->lock. wake_q_add() grabs reference to p.
1394          */
1395         wake_q_add(wake_q, p);
1396         __unqueue_futex(q);
1397         /*
1398          * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
1399          * is written, without taking any locks. This is possible in the event
1400          * of a spurious wakeup, for example. A memory barrier is required here
1401          * to prevent the following store to lock_ptr from getting ahead of the
1402          * plist_del in __unqueue_futex().
1403          */
1404         smp_store_release(&q->lock_ptr, NULL);
1405 }
1406
1407 /*
1408  * Caller must hold a reference on @pi_state.
1409  */
1410 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
1411 {
1412         u32 uninitialized_var(curval), newval;
1413         struct task_struct *new_owner;
1414         bool postunlock = false;
1415         DEFINE_WAKE_Q(wake_q);
1416         int ret = 0;
1417
1418         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1419         if (WARN_ON_ONCE(!new_owner)) {
1420                 /*
1421                  * As per the comment in futex_unlock_pi() this should not happen.
1422                  *
1423                  * When this happens, give up our locks and try again, giving
1424                  * the futex_lock_pi() instance time to complete, either by
1425                  * waiting on the rtmutex or removing itself from the futex
1426                  * queue.
1427                  */
1428                 ret = -EAGAIN;
1429                 goto out_unlock;
1430         }
1431
1432         /*
1433          * We pass it to the next owner. The WAITERS bit is always kept
1434          * enabled while there is PI state around. We cleanup the owner
1435          * died bit, because we are the owner.
1436          */
1437         newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1438
1439         if (unlikely(should_fail_futex(true)))
1440                 ret = -EFAULT;
1441
1442         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
1443                 ret = -EFAULT;
1444
1445         } else if (curval != uval) {
1446                 /*
1447                  * If a unconditional UNLOCK_PI operation (user space did not
1448                  * try the TID->0 transition) raced with a waiter setting the
1449                  * FUTEX_WAITERS flag between get_user() and locking the hash
1450                  * bucket lock, retry the operation.
1451                  */
1452                 if ((FUTEX_TID_MASK & curval) == uval)
1453                         ret = -EAGAIN;
1454                 else
1455                         ret = -EINVAL;
1456         }
1457
1458         if (ret)
1459                 goto out_unlock;
1460
1461         /*
1462          * This is a point of no return; once we modify the uval there is no
1463          * going back and subsequent operations must not fail.
1464          */
1465
1466         raw_spin_lock(&pi_state->owner->pi_lock);
1467         WARN_ON(list_empty(&pi_state->list));
1468         list_del_init(&pi_state->list);
1469         raw_spin_unlock(&pi_state->owner->pi_lock);
1470
1471         raw_spin_lock(&new_owner->pi_lock);
1472         WARN_ON(!list_empty(&pi_state->list));
1473         list_add(&pi_state->list, &new_owner->pi_state_list);
1474         pi_state->owner = new_owner;
1475         raw_spin_unlock(&new_owner->pi_lock);
1476
1477         postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1478
1479 out_unlock:
1480         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1481
1482         if (postunlock)
1483                 rt_mutex_postunlock(&wake_q);
1484
1485         return ret;
1486 }
1487
1488 /*
1489  * Express the locking dependencies for lockdep:
1490  */
1491 static inline void
1492 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1493 {
1494         if (hb1 <= hb2) {
1495                 spin_lock(&hb1->lock);
1496                 if (hb1 < hb2)
1497                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1498         } else { /* hb1 > hb2 */
1499                 spin_lock(&hb2->lock);
1500                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1501         }
1502 }
1503
1504 static inline void
1505 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1506 {
1507         spin_unlock(&hb1->lock);
1508         if (hb1 != hb2)
1509                 spin_unlock(&hb2->lock);
1510 }
1511
1512 /*
1513  * Wake up waiters matching bitset queued on this futex (uaddr).
1514  */
1515 static int
1516 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1517 {
1518         struct futex_hash_bucket *hb;
1519         struct futex_q *this, *next;
1520         union futex_key key = FUTEX_KEY_INIT;
1521         int ret;
1522         DEFINE_WAKE_Q(wake_q);
1523
1524         if (!bitset)
1525                 return -EINVAL;
1526
1527         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1528         if (unlikely(ret != 0))
1529                 goto out;
1530
1531         hb = hash_futex(&key);
1532
1533         /* Make sure we really have tasks to wakeup */
1534         if (!hb_waiters_pending(hb))
1535                 goto out_put_key;
1536
1537         spin_lock(&hb->lock);
1538
1539         plist_for_each_entry_safe(this, next, &hb->chain, list) {
1540                 if (match_futex (&this->key, &key)) {
1541                         if (this->pi_state || this->rt_waiter) {
1542                                 ret = -EINVAL;
1543                                 break;
1544                         }
1545
1546                         /* Check if one of the bits is set in both bitsets */
1547                         if (!(this->bitset & bitset))
1548                                 continue;
1549
1550                         mark_wake_futex(&wake_q, this);
1551                         if (++ret >= nr_wake)
1552                                 break;
1553                 }
1554         }
1555
1556         spin_unlock(&hb->lock);
1557         wake_up_q(&wake_q);
1558 out_put_key:
1559         put_futex_key(&key);
1560 out:
1561         return ret;
1562 }
1563
1564 static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
1565 {
1566         unsigned int op =         (encoded_op & 0x70000000) >> 28;
1567         unsigned int cmp =        (encoded_op & 0x0f000000) >> 24;
1568         int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 12);
1569         int cmparg = sign_extend32(encoded_op & 0x00000fff, 12);
1570         int oldval, ret;
1571
1572         if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
1573                 if (oparg < 0 || oparg > 31)
1574                         return -EINVAL;
1575                 oparg = 1 << oparg;
1576         }
1577
1578         if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
1579                 return -EFAULT;
1580
1581         ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
1582         if (ret)
1583                 return ret;
1584
1585         switch (cmp) {
1586         case FUTEX_OP_CMP_EQ:
1587                 return oldval == cmparg;
1588         case FUTEX_OP_CMP_NE:
1589                 return oldval != cmparg;
1590         case FUTEX_OP_CMP_LT:
1591                 return oldval < cmparg;
1592         case FUTEX_OP_CMP_GE:
1593                 return oldval >= cmparg;
1594         case FUTEX_OP_CMP_LE:
1595                 return oldval <= cmparg;
1596         case FUTEX_OP_CMP_GT:
1597                 return oldval > cmparg;
1598         default:
1599                 return -ENOSYS;
1600         }
1601 }
1602
1603 /*
1604  * Wake up all waiters hashed on the physical page that is mapped
1605  * to this virtual address:
1606  */
1607 static int
1608 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1609               int nr_wake, int nr_wake2, int op)
1610 {
1611         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1612         struct futex_hash_bucket *hb1, *hb2;
1613         struct futex_q *this, *next;
1614         int ret, op_ret;
1615         DEFINE_WAKE_Q(wake_q);
1616
1617 retry:
1618         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1619         if (unlikely(ret != 0))
1620                 goto out;
1621         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1622         if (unlikely(ret != 0))
1623                 goto out_put_key1;
1624
1625         hb1 = hash_futex(&key1);
1626         hb2 = hash_futex(&key2);
1627
1628 retry_private:
1629         double_lock_hb(hb1, hb2);
1630         op_ret = futex_atomic_op_inuser(op, uaddr2);
1631         if (unlikely(op_ret < 0)) {
1632
1633                 double_unlock_hb(hb1, hb2);
1634
1635 #ifndef CONFIG_MMU
1636                 /*
1637                  * we don't get EFAULT from MMU faults if we don't have an MMU,
1638                  * but we might get them from range checking
1639                  */
1640                 ret = op_ret;
1641                 goto out_put_keys;
1642 #endif
1643
1644                 if (unlikely(op_ret != -EFAULT)) {
1645                         ret = op_ret;
1646                         goto out_put_keys;
1647                 }
1648
1649                 ret = fault_in_user_writeable(uaddr2);
1650                 if (ret)
1651                         goto out_put_keys;
1652
1653                 if (!(flags & FLAGS_SHARED))
1654                         goto retry_private;
1655
1656                 put_futex_key(&key2);
1657                 put_futex_key(&key1);
1658                 goto retry;
1659         }
1660
1661         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1662                 if (match_futex (&this->key, &key1)) {
1663                         if (this->pi_state || this->rt_waiter) {
1664                                 ret = -EINVAL;
1665                                 goto out_unlock;
1666                         }
1667                         mark_wake_futex(&wake_q, this);
1668                         if (++ret >= nr_wake)
1669                                 break;
1670                 }
1671         }
1672
1673         if (op_ret > 0) {
1674                 op_ret = 0;
1675                 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1676                         if (match_futex (&this->key, &key2)) {
1677                                 if (this->pi_state || this->rt_waiter) {
1678                                         ret = -EINVAL;
1679                                         goto out_unlock;
1680                                 }
1681                                 mark_wake_futex(&wake_q, this);
1682                                 if (++op_ret >= nr_wake2)
1683                                         break;
1684                         }
1685                 }
1686                 ret += op_ret;
1687         }
1688
1689 out_unlock:
1690         double_unlock_hb(hb1, hb2);
1691         wake_up_q(&wake_q);
1692 out_put_keys:
1693         put_futex_key(&key2);
1694 out_put_key1:
1695         put_futex_key(&key1);
1696 out:
1697         return ret;
1698 }
1699
1700 /**
1701  * requeue_futex() - Requeue a futex_q from one hb to another
1702  * @q:          the futex_q to requeue
1703  * @hb1:        the source hash_bucket
1704  * @hb2:        the target hash_bucket
1705  * @key2:       the new key for the requeued futex_q
1706  */
1707 static inline
1708 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1709                    struct futex_hash_bucket *hb2, union futex_key *key2)
1710 {
1711
1712         /*
1713          * If key1 and key2 hash to the same bucket, no need to
1714          * requeue.
1715          */
1716         if (likely(&hb1->chain != &hb2->chain)) {
1717                 plist_del(&q->list, &hb1->chain);
1718                 hb_waiters_dec(hb1);
1719                 hb_waiters_inc(hb2);
1720                 plist_add(&q->list, &hb2->chain);
1721                 q->lock_ptr = &hb2->lock;
1722         }
1723         get_futex_key_refs(key2);
1724         q->key = *key2;
1725 }
1726
1727 /**
1728  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1729  * @q:          the futex_q
1730  * @key:        the key of the requeue target futex
1731  * @hb:         the hash_bucket of the requeue target futex
1732  *
1733  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1734  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1735  * to the requeue target futex so the waiter can detect the wakeup on the right
1736  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1737  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1738  * to protect access to the pi_state to fixup the owner later.  Must be called
1739  * with both q->lock_ptr and hb->lock held.
1740  */
1741 static inline
1742 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1743                            struct futex_hash_bucket *hb)
1744 {
1745         get_futex_key_refs(key);
1746         q->key = *key;
1747
1748         __unqueue_futex(q);
1749
1750         WARN_ON(!q->rt_waiter);
1751         q->rt_waiter = NULL;
1752
1753         q->lock_ptr = &hb->lock;
1754
1755         wake_up_state(q->task, TASK_NORMAL);
1756 }
1757
1758 /**
1759  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1760  * @pifutex:            the user address of the to futex
1761  * @hb1:                the from futex hash bucket, must be locked by the caller
1762  * @hb2:                the to futex hash bucket, must be locked by the caller
1763  * @key1:               the from futex key
1764  * @key2:               the to futex key
1765  * @ps:                 address to store the pi_state pointer
1766  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1767  *
1768  * Try and get the lock on behalf of the top waiter if we can do it atomically.
1769  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1770  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1771  * hb1 and hb2 must be held by the caller.
1772  *
1773  * Return:
1774  *  -  0 - failed to acquire the lock atomically;
1775  *  - >0 - acquired the lock, return value is vpid of the top_waiter
1776  *  - <0 - error
1777  */
1778 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1779                                  struct futex_hash_bucket *hb1,
1780                                  struct futex_hash_bucket *hb2,
1781                                  union futex_key *key1, union futex_key *key2,
1782                                  struct futex_pi_state **ps, int set_waiters)
1783 {
1784         struct futex_q *top_waiter = NULL;
1785         u32 curval;
1786         int ret, vpid;
1787
1788         if (get_futex_value_locked(&curval, pifutex))
1789                 return -EFAULT;
1790
1791         if (unlikely(should_fail_futex(true)))
1792                 return -EFAULT;
1793
1794         /*
1795          * Find the top_waiter and determine if there are additional waiters.
1796          * If the caller intends to requeue more than 1 waiter to pifutex,
1797          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1798          * as we have means to handle the possible fault.  If not, don't set
1799          * the bit unecessarily as it will force the subsequent unlock to enter
1800          * the kernel.
1801          */
1802         top_waiter = futex_top_waiter(hb1, key1);
1803
1804         /* There are no waiters, nothing for us to do. */
1805         if (!top_waiter)
1806                 return 0;
1807
1808         /* Ensure we requeue to the expected futex. */
1809         if (!match_futex(top_waiter->requeue_pi_key, key2))
1810                 return -EINVAL;
1811
1812         /*
1813          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1814          * the contended case or if set_waiters is 1.  The pi_state is returned
1815          * in ps in contended cases.
1816          */
1817         vpid = task_pid_vnr(top_waiter->task);
1818         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1819                                    set_waiters);
1820         if (ret == 1) {
1821                 requeue_pi_wake_futex(top_waiter, key2, hb2);
1822                 return vpid;
1823         }
1824         return ret;
1825 }
1826
1827 /**
1828  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1829  * @uaddr1:     source futex user address
1830  * @flags:      futex flags (FLAGS_SHARED, etc.)
1831  * @uaddr2:     target futex user address
1832  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1833  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1834  * @cmpval:     @uaddr1 expected value (or %NULL)
1835  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1836  *              pi futex (pi to pi requeue is not supported)
1837  *
1838  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1839  * uaddr2 atomically on behalf of the top waiter.
1840  *
1841  * Return:
1842  *  - >=0 - on success, the number of tasks requeued or woken;
1843  *  -  <0 - on error
1844  */
1845 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1846                          u32 __user *uaddr2, int nr_wake, int nr_requeue,
1847                          u32 *cmpval, int requeue_pi)
1848 {
1849         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1850         int drop_count = 0, task_count = 0, ret;
1851         struct futex_pi_state *pi_state = NULL;
1852         struct futex_hash_bucket *hb1, *hb2;
1853         struct futex_q *this, *next;
1854         DEFINE_WAKE_Q(wake_q);
1855
1856         /*
1857          * When PI not supported: return -ENOSYS if requeue_pi is true,
1858          * consequently the compiler knows requeue_pi is always false past
1859          * this point which will optimize away all the conditional code
1860          * further down.
1861          */
1862         if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
1863                 return -ENOSYS;
1864
1865         if (requeue_pi) {
1866                 /*
1867                  * Requeue PI only works on two distinct uaddrs. This
1868                  * check is only valid for private futexes. See below.
1869                  */
1870                 if (uaddr1 == uaddr2)
1871                         return -EINVAL;
1872
1873                 /*
1874                  * requeue_pi requires a pi_state, try to allocate it now
1875                  * without any locks in case it fails.
1876                  */
1877                 if (refill_pi_state_cache())
1878                         return -ENOMEM;
1879                 /*
1880                  * requeue_pi must wake as many tasks as it can, up to nr_wake
1881                  * + nr_requeue, since it acquires the rt_mutex prior to
1882                  * returning to userspace, so as to not leave the rt_mutex with
1883                  * waiters and no owner.  However, second and third wake-ups
1884                  * cannot be predicted as they involve race conditions with the
1885                  * first wake and a fault while looking up the pi_state.  Both
1886                  * pthread_cond_signal() and pthread_cond_broadcast() should
1887                  * use nr_wake=1.
1888                  */
1889                 if (nr_wake != 1)
1890                         return -EINVAL;
1891         }
1892
1893 retry:
1894         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1895         if (unlikely(ret != 0))
1896                 goto out;
1897         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1898                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1899         if (unlikely(ret != 0))
1900                 goto out_put_key1;
1901
1902         /*
1903          * The check above which compares uaddrs is not sufficient for
1904          * shared futexes. We need to compare the keys:
1905          */
1906         if (requeue_pi && match_futex(&key1, &key2)) {
1907                 ret = -EINVAL;
1908                 goto out_put_keys;
1909         }
1910
1911         hb1 = hash_futex(&key1);
1912         hb2 = hash_futex(&key2);
1913
1914 retry_private:
1915         hb_waiters_inc(hb2);
1916         double_lock_hb(hb1, hb2);
1917
1918         if (likely(cmpval != NULL)) {
1919                 u32 curval;
1920
1921                 ret = get_futex_value_locked(&curval, uaddr1);
1922
1923                 if (unlikely(ret)) {
1924                         double_unlock_hb(hb1, hb2);
1925                         hb_waiters_dec(hb2);
1926
1927                         ret = get_user(curval, uaddr1);
1928                         if (ret)
1929                                 goto out_put_keys;
1930
1931                         if (!(flags & FLAGS_SHARED))
1932                                 goto retry_private;
1933
1934                         put_futex_key(&key2);
1935                         put_futex_key(&key1);
1936                         goto retry;
1937                 }
1938                 if (curval != *cmpval) {
1939                         ret = -EAGAIN;
1940                         goto out_unlock;
1941                 }
1942         }
1943
1944         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1945                 /*
1946                  * Attempt to acquire uaddr2 and wake the top waiter. If we
1947                  * intend to requeue waiters, force setting the FUTEX_WAITERS
1948                  * bit.  We force this here where we are able to easily handle
1949                  * faults rather in the requeue loop below.
1950                  */
1951                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1952                                                  &key2, &pi_state, nr_requeue);
1953
1954                 /*
1955                  * At this point the top_waiter has either taken uaddr2 or is
1956                  * waiting on it.  If the former, then the pi_state will not
1957                  * exist yet, look it up one more time to ensure we have a
1958                  * reference to it. If the lock was taken, ret contains the
1959                  * vpid of the top waiter task.
1960                  * If the lock was not taken, we have pi_state and an initial
1961                  * refcount on it. In case of an error we have nothing.
1962                  */
1963                 if (ret > 0) {
1964                         WARN_ON(pi_state);
1965                         drop_count++;
1966                         task_count++;
1967                         /*
1968                          * If we acquired the lock, then the user space value
1969                          * of uaddr2 should be vpid. It cannot be changed by
1970                          * the top waiter as it is blocked on hb2 lock if it
1971                          * tries to do so. If something fiddled with it behind
1972                          * our back the pi state lookup might unearth it. So
1973                          * we rather use the known value than rereading and
1974                          * handing potential crap to lookup_pi_state.
1975                          *
1976                          * If that call succeeds then we have pi_state and an
1977                          * initial refcount on it.
1978                          */
1979                         ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
1980                 }
1981
1982                 switch (ret) {
1983                 case 0:
1984                         /* We hold a reference on the pi state. */
1985                         break;
1986
1987                         /* If the above failed, then pi_state is NULL */
1988                 case -EFAULT:
1989                         double_unlock_hb(hb1, hb2);
1990                         hb_waiters_dec(hb2);
1991                         put_futex_key(&key2);
1992                         put_futex_key(&key1);
1993                         ret = fault_in_user_writeable(uaddr2);
1994                         if (!ret)
1995                                 goto retry;
1996                         goto out;
1997                 case -EAGAIN:
1998                         /*
1999                          * Two reasons for this:
2000                          * - Owner is exiting and we just wait for the
2001                          *   exit to complete.
2002                          * - The user space value changed.
2003                          */
2004                         double_unlock_hb(hb1, hb2);
2005                         hb_waiters_dec(hb2);
2006                         put_futex_key(&key2);
2007                         put_futex_key(&key1);
2008                         cond_resched();
2009                         goto retry;
2010                 default:
2011                         goto out_unlock;
2012                 }
2013         }
2014
2015         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
2016                 if (task_count - nr_wake >= nr_requeue)
2017                         break;
2018
2019                 if (!match_futex(&this->key, &key1))
2020                         continue;
2021
2022                 /*
2023                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
2024                  * be paired with each other and no other futex ops.
2025                  *
2026                  * We should never be requeueing a futex_q with a pi_state,
2027                  * which is awaiting a futex_unlock_pi().
2028                  */
2029                 if ((requeue_pi && !this->rt_waiter) ||
2030                     (!requeue_pi && this->rt_waiter) ||
2031                     this->pi_state) {
2032                         ret = -EINVAL;
2033                         break;
2034                 }
2035
2036                 /*
2037                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
2038                  * lock, we already woke the top_waiter.  If not, it will be
2039                  * woken by futex_unlock_pi().
2040                  */
2041                 if (++task_count <= nr_wake && !requeue_pi) {
2042                         mark_wake_futex(&wake_q, this);
2043                         continue;
2044                 }
2045
2046                 /* Ensure we requeue to the expected futex for requeue_pi. */
2047                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
2048                         ret = -EINVAL;
2049                         break;
2050                 }
2051
2052                 /*
2053                  * Requeue nr_requeue waiters and possibly one more in the case
2054                  * of requeue_pi if we couldn't acquire the lock atomically.
2055                  */
2056                 if (requeue_pi) {
2057                         /*
2058                          * Prepare the waiter to take the rt_mutex. Take a
2059                          * refcount on the pi_state and store the pointer in
2060                          * the futex_q object of the waiter.
2061                          */
2062                         get_pi_state(pi_state);
2063                         this->pi_state = pi_state;
2064                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
2065                                                         this->rt_waiter,
2066                                                         this->task);
2067                         if (ret == 1) {
2068                                 /*
2069                                  * We got the lock. We do neither drop the
2070                                  * refcount on pi_state nor clear
2071                                  * this->pi_state because the waiter needs the
2072                                  * pi_state for cleaning up the user space
2073                                  * value. It will drop the refcount after
2074                                  * doing so.
2075                                  */
2076                                 requeue_pi_wake_futex(this, &key2, hb2);
2077                                 drop_count++;
2078                                 continue;
2079                         } else if (ret) {
2080                                 /*
2081                                  * rt_mutex_start_proxy_lock() detected a
2082                                  * potential deadlock when we tried to queue
2083                                  * that waiter. Drop the pi_state reference
2084                                  * which we took above and remove the pointer
2085                                  * to the state from the waiters futex_q
2086                                  * object.
2087                                  */
2088                                 this->pi_state = NULL;
2089                                 put_pi_state(pi_state);
2090                                 /*
2091                                  * We stop queueing more waiters and let user
2092                                  * space deal with the mess.
2093                                  */
2094                                 break;
2095                         }
2096                 }
2097                 requeue_futex(this, hb1, hb2, &key2);
2098                 drop_count++;
2099         }
2100
2101         /*
2102          * We took an extra initial reference to the pi_state either
2103          * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
2104          * need to drop it here again.
2105          */
2106         put_pi_state(pi_state);
2107
2108 out_unlock:
2109         double_unlock_hb(hb1, hb2);
2110         wake_up_q(&wake_q);
2111         hb_waiters_dec(hb2);
2112
2113         /*
2114          * drop_futex_key_refs() must be called outside the spinlocks. During
2115          * the requeue we moved futex_q's from the hash bucket at key1 to the
2116          * one at key2 and updated their key pointer.  We no longer need to
2117          * hold the references to key1.
2118          */
2119         while (--drop_count >= 0)
2120                 drop_futex_key_refs(&key1);
2121
2122 out_put_keys:
2123         put_futex_key(&key2);
2124 out_put_key1:
2125         put_futex_key(&key1);
2126 out:
2127         return ret ? ret : task_count;
2128 }
2129
2130 /* The key must be already stored in q->key. */
2131 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
2132         __acquires(&hb->lock)
2133 {
2134         struct futex_hash_bucket *hb;
2135
2136         hb = hash_futex(&q->key);
2137
2138         /*
2139          * Increment the counter before taking the lock so that
2140          * a potential waker won't miss a to-be-slept task that is
2141          * waiting for the spinlock. This is safe as all queue_lock()
2142          * users end up calling queue_me(). Similarly, for housekeeping,
2143          * decrement the counter at queue_unlock() when some error has
2144          * occurred and we don't end up adding the task to the list.
2145          */
2146         hb_waiters_inc(hb);
2147
2148         q->lock_ptr = &hb->lock;
2149
2150         spin_lock(&hb->lock); /* implies smp_mb(); (A) */
2151         return hb;
2152 }
2153
2154 static inline void
2155 queue_unlock(struct futex_hash_bucket *hb)
2156         __releases(&hb->lock)
2157 {
2158         spin_unlock(&hb->lock);
2159         hb_waiters_dec(hb);
2160 }
2161
2162 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2163 {
2164         int prio;
2165
2166         /*
2167          * The priority used to register this element is
2168          * - either the real thread-priority for the real-time threads
2169          * (i.e. threads with a priority lower than MAX_RT_PRIO)
2170          * - or MAX_RT_PRIO for non-RT threads.
2171          * Thus, all RT-threads are woken first in priority order, and
2172          * the others are woken last, in FIFO order.
2173          */
2174         prio = min(current->normal_prio, MAX_RT_PRIO);
2175
2176         plist_node_init(&q->list, prio);
2177         plist_add(&q->list, &hb->chain);
2178         q->task = current;
2179 }
2180
2181 /**
2182  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
2183  * @q:  The futex_q to enqueue
2184  * @hb: The destination hash bucket
2185  *
2186  * The hb->lock must be held by the caller, and is released here. A call to
2187  * queue_me() is typically paired with exactly one call to unqueue_me().  The
2188  * exceptions involve the PI related operations, which may use unqueue_me_pi()
2189  * or nothing if the unqueue is done as part of the wake process and the unqueue
2190  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
2191  * an example).
2192  */
2193 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2194         __releases(&hb->lock)
2195 {
2196         __queue_me(q, hb);
2197         spin_unlock(&hb->lock);
2198 }
2199
2200 /**
2201  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
2202  * @q:  The futex_q to unqueue
2203  *
2204  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
2205  * be paired with exactly one earlier call to queue_me().
2206  *
2207  * Return:
2208  *  - 1 - if the futex_q was still queued (and we removed unqueued it);
2209  *  - 0 - if the futex_q was already removed by the waking thread
2210  */
2211 static int unqueue_me(struct futex_q *q)
2212 {
2213         spinlock_t *lock_ptr;
2214         int ret = 0;
2215
2216         /* In the common case we don't take the spinlock, which is nice. */
2217 retry:
2218         /*
2219          * q->lock_ptr can change between this read and the following spin_lock.
2220          * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
2221          * optimizing lock_ptr out of the logic below.
2222          */
2223         lock_ptr = READ_ONCE(q->lock_ptr);
2224         if (lock_ptr != NULL) {
2225                 spin_lock(lock_ptr);
2226                 /*
2227                  * q->lock_ptr can change between reading it and
2228                  * spin_lock(), causing us to take the wrong lock.  This
2229                  * corrects the race condition.
2230                  *
2231                  * Reasoning goes like this: if we have the wrong lock,
2232                  * q->lock_ptr must have changed (maybe several times)
2233                  * between reading it and the spin_lock().  It can
2234                  * change again after the spin_lock() but only if it was
2235                  * already changed before the spin_lock().  It cannot,
2236                  * however, change back to the original value.  Therefore
2237                  * we can detect whether we acquired the correct lock.
2238                  */
2239                 if (unlikely(lock_ptr != q->lock_ptr)) {
2240                         spin_unlock(lock_ptr);
2241                         goto retry;
2242                 }
2243                 __unqueue_futex(q);
2244
2245                 BUG_ON(q->pi_state);
2246
2247                 spin_unlock(lock_ptr);
2248                 ret = 1;
2249         }
2250
2251         drop_futex_key_refs(&q->key);
2252         return ret;
2253 }
2254
2255 /*
2256  * PI futexes can not be requeued and must remove themself from the
2257  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
2258  * and dropped here.
2259  */
2260 static void unqueue_me_pi(struct futex_q *q)
2261         __releases(q->lock_ptr)
2262 {
2263         __unqueue_futex(q);
2264
2265         BUG_ON(!q->pi_state);
2266         put_pi_state(q->pi_state);
2267         q->pi_state = NULL;
2268
2269         spin_unlock(q->lock_ptr);
2270 }
2271
2272 /*
2273  * Fixup the pi_state owner with the new owner.
2274  *
2275  * Must be called with hash bucket lock held and mm->sem held for non
2276  * private futexes.
2277  */
2278 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2279                                 struct task_struct *newowner)
2280 {
2281         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2282         struct futex_pi_state *pi_state = q->pi_state;
2283         u32 uval, uninitialized_var(curval), newval;
2284         struct task_struct *oldowner;
2285         int ret;
2286
2287         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2288
2289         oldowner = pi_state->owner;
2290         /* Owner died? */
2291         if (!pi_state->owner)
2292                 newtid |= FUTEX_OWNER_DIED;
2293
2294         /*
2295          * We are here either because we stole the rtmutex from the
2296          * previous highest priority waiter or we are the highest priority
2297          * waiter but have failed to get the rtmutex the first time.
2298          *
2299          * We have to replace the newowner TID in the user space variable.
2300          * This must be atomic as we have to preserve the owner died bit here.
2301          *
2302          * Note: We write the user space value _before_ changing the pi_state
2303          * because we can fault here. Imagine swapped out pages or a fork
2304          * that marked all the anonymous memory readonly for cow.
2305          *
2306          * Modifying pi_state _before_ the user space value would leave the
2307          * pi_state in an inconsistent state when we fault here, because we
2308          * need to drop the locks to handle the fault. This might be observed
2309          * in the PID check in lookup_pi_state.
2310          */
2311 retry:
2312         if (get_futex_value_locked(&uval, uaddr))
2313                 goto handle_fault;
2314
2315         for (;;) {
2316                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2317
2318                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
2319                         goto handle_fault;
2320                 if (curval == uval)
2321                         break;
2322                 uval = curval;
2323         }
2324
2325         /*
2326          * We fixed up user space. Now we need to fix the pi_state
2327          * itself.
2328          */
2329         if (pi_state->owner != NULL) {
2330                 raw_spin_lock(&pi_state->owner->pi_lock);
2331                 WARN_ON(list_empty(&pi_state->list));
2332                 list_del_init(&pi_state->list);
2333                 raw_spin_unlock(&pi_state->owner->pi_lock);
2334         }
2335
2336         pi_state->owner = newowner;
2337
2338         raw_spin_lock(&newowner->pi_lock);
2339         WARN_ON(!list_empty(&pi_state->list));
2340         list_add(&pi_state->list, &newowner->pi_state_list);
2341         raw_spin_unlock(&newowner->pi_lock);
2342         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2343
2344         return 0;
2345
2346         /*
2347          * To handle the page fault we need to drop the locks here. That gives
2348          * the other task (either the highest priority waiter itself or the
2349          * task which stole the rtmutex) the chance to try the fixup of the
2350          * pi_state. So once we are back from handling the fault we need to
2351          * check the pi_state after reacquiring the locks and before trying to
2352          * do another fixup. When the fixup has been done already we simply
2353          * return.
2354          *
2355          * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
2356          * drop hb->lock since the caller owns the hb -> futex_q relation.
2357          * Dropping the pi_mutex->wait_lock requires the state revalidate.
2358          */
2359 handle_fault:
2360         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2361         spin_unlock(q->lock_ptr);
2362
2363         ret = fault_in_user_writeable(uaddr);
2364
2365         spin_lock(q->lock_ptr);
2366         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2367
2368         /*
2369          * Check if someone else fixed it for us:
2370          */
2371         if (pi_state->owner != oldowner) {
2372                 ret = 0;
2373                 goto out_unlock;
2374         }
2375
2376         if (ret)
2377                 goto out_unlock;
2378
2379         goto retry;
2380
2381 out_unlock:
2382         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2383         return ret;
2384 }
2385
2386 static long futex_wait_restart(struct restart_block *restart);
2387
2388 /**
2389  * fixup_owner() - Post lock pi_state and corner case management
2390  * @uaddr:      user address of the futex
2391  * @q:          futex_q (contains pi_state and access to the rt_mutex)
2392  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
2393  *
2394  * After attempting to lock an rt_mutex, this function is called to cleanup
2395  * the pi_state owner as well as handle race conditions that may allow us to
2396  * acquire the lock. Must be called with the hb lock held.
2397  *
2398  * Return:
2399  *  -  1 - success, lock taken;
2400  *  -  0 - success, lock not taken;
2401  *  - <0 - on error (-EFAULT)
2402  */
2403 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2404 {
2405         int ret = 0;
2406
2407         if (locked) {
2408                 /*
2409                  * Got the lock. We might not be the anticipated owner if we
2410                  * did a lock-steal - fix up the PI-state in that case:
2411                  *
2412                  * We can safely read pi_state->owner without holding wait_lock
2413                  * because we now own the rt_mutex, only the owner will attempt
2414                  * to change it.
2415                  */
2416                 if (q->pi_state->owner != current)
2417                         ret = fixup_pi_state_owner(uaddr, q, current);
2418                 goto out;
2419         }
2420
2421         /*
2422          * Paranoia check. If we did not take the lock, then we should not be
2423          * the owner of the rt_mutex.
2424          */
2425         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
2426                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2427                                 "pi-state %p\n", ret,
2428                                 q->pi_state->pi_mutex.owner,
2429                                 q->pi_state->owner);
2430         }
2431
2432 out:
2433         return ret ? ret : locked;
2434 }
2435
2436 /**
2437  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2438  * @hb:         the futex hash bucket, must be locked by the caller
2439  * @q:          the futex_q to queue up on
2440  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
2441  */
2442 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2443                                 struct hrtimer_sleeper *timeout)
2444 {
2445         /*
2446          * The task state is guaranteed to be set before another task can
2447          * wake it. set_current_state() is implemented using smp_store_mb() and
2448          * queue_me() calls spin_unlock() upon completion, both serializing
2449          * access to the hash list and forcing another memory barrier.
2450          */
2451         set_current_state(TASK_INTERRUPTIBLE);
2452         queue_me(q, hb);
2453
2454         /* Arm the timer */
2455         if (timeout)
2456                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2457
2458         /*
2459          * If we have been removed from the hash list, then another task
2460          * has tried to wake us, and we can skip the call to schedule().
2461          */
2462         if (likely(!plist_node_empty(&q->list))) {
2463                 /*
2464                  * If the timer has already expired, current will already be
2465                  * flagged for rescheduling. Only call schedule if there
2466                  * is no timeout, or if it has yet to expire.
2467                  */
2468                 if (!timeout || timeout->task)
2469                         freezable_schedule();
2470         }
2471         __set_current_state(TASK_RUNNING);
2472 }
2473
2474 /**
2475  * futex_wait_setup() - Prepare to wait on a futex
2476  * @uaddr:      the futex userspace address
2477  * @val:        the expected value
2478  * @flags:      futex flags (FLAGS_SHARED, etc.)
2479  * @q:          the associated futex_q
2480  * @hb:         storage for hash_bucket pointer to be returned to caller
2481  *
2482  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
2483  * compare it with the expected value.  Handle atomic faults internally.
2484  * Return with the hb lock held and a q.key reference on success, and unlocked
2485  * with no q.key reference on failure.
2486  *
2487  * Return:
2488  *  -  0 - uaddr contains val and hb has been locked;
2489  *  - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2490  */
2491 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2492                            struct futex_q *q, struct futex_hash_bucket **hb)
2493 {
2494         u32 uval;
2495         int ret;
2496
2497         /*
2498          * Access the page AFTER the hash-bucket is locked.
2499          * Order is important:
2500          *
2501          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2502          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
2503          *
2504          * The basic logical guarantee of a futex is that it blocks ONLY
2505          * if cond(var) is known to be true at the time of blocking, for
2506          * any cond.  If we locked the hash-bucket after testing *uaddr, that
2507          * would open a race condition where we could block indefinitely with
2508          * cond(var) false, which would violate the guarantee.
2509          *
2510          * On the other hand, we insert q and release the hash-bucket only
2511          * after testing *uaddr.  This guarantees that futex_wait() will NOT
2512          * absorb a wakeup if *uaddr does not match the desired values
2513          * while the syscall executes.
2514          */
2515 retry:
2516         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2517         if (unlikely(ret != 0))
2518                 return ret;
2519
2520 retry_private:
2521         *hb = queue_lock(q);
2522
2523         ret = get_futex_value_locked(&uval, uaddr);
2524
2525         if (ret) {
2526                 queue_unlock(*hb);
2527
2528                 ret = get_user(uval, uaddr);
2529                 if (ret)
2530                         goto out;
2531
2532                 if (!(flags & FLAGS_SHARED))
2533                         goto retry_private;
2534
2535                 put_futex_key(&q->key);
2536                 goto retry;
2537         }
2538
2539         if (uval != val) {
2540                 queue_unlock(*hb);
2541                 ret = -EWOULDBLOCK;
2542         }
2543
2544 out:
2545         if (ret)
2546                 put_futex_key(&q->key);
2547         return ret;
2548 }
2549
2550 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2551                       ktime_t *abs_time, u32 bitset)
2552 {
2553         struct hrtimer_sleeper timeout, *to = NULL;
2554         struct restart_block *restart;
2555         struct futex_hash_bucket *hb;
2556         struct futex_q q = futex_q_init;
2557         int ret;
2558
2559         if (!bitset)
2560                 return -EINVAL;
2561         q.bitset = bitset;
2562
2563         if (abs_time) {
2564                 to = &timeout;
2565
2566                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2567                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
2568                                       HRTIMER_MODE_ABS);
2569                 hrtimer_init_sleeper(to, current);
2570                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2571                                              current->timer_slack_ns);
2572         }
2573
2574 retry:
2575         /*
2576          * Prepare to wait on uaddr. On success, holds hb lock and increments
2577          * q.key refs.
2578          */
2579         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2580         if (ret)
2581                 goto out;
2582
2583         /* queue_me and wait for wakeup, timeout, or a signal. */
2584         futex_wait_queue_me(hb, &q, to);
2585
2586         /* If we were woken (and unqueued), we succeeded, whatever. */
2587         ret = 0;
2588         /* unqueue_me() drops q.key ref */
2589         if (!unqueue_me(&q))
2590                 goto out;
2591         ret = -ETIMEDOUT;
2592         if (to && !to->task)
2593                 goto out;
2594
2595         /*
2596          * We expect signal_pending(current), but we might be the
2597          * victim of a spurious wakeup as well.
2598          */
2599         if (!signal_pending(current))
2600                 goto retry;
2601
2602         ret = -ERESTARTSYS;
2603         if (!abs_time)
2604                 goto out;
2605
2606         restart = &current->restart_block;
2607         restart->fn = futex_wait_restart;
2608         restart->futex.uaddr = uaddr;
2609         restart->futex.val = val;
2610         restart->futex.time = *abs_time;
2611         restart->futex.bitset = bitset;
2612         restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2613
2614         ret = -ERESTART_RESTARTBLOCK;
2615
2616 out:
2617         if (to) {
2618                 hrtimer_cancel(&to->timer);
2619                 destroy_hrtimer_on_stack(&to->timer);
2620         }
2621         return ret;
2622 }
2623
2624
2625 static long futex_wait_restart(struct restart_block *restart)
2626 {
2627         u32 __user *uaddr = restart->futex.uaddr;
2628         ktime_t t, *tp = NULL;
2629
2630         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2631                 t = restart->futex.time;
2632                 tp = &t;
2633         }
2634         restart->fn = do_no_restart_syscall;
2635
2636         return (long)futex_wait(uaddr, restart->futex.flags,
2637                                 restart->futex.val, tp, restart->futex.bitset);
2638 }
2639
2640
2641 /*
2642  * Userspace tried a 0 -> TID atomic transition of the futex value
2643  * and failed. The kernel side here does the whole locking operation:
2644  * if there are waiters then it will block as a consequence of relying
2645  * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2646  * a 0 value of the futex too.).
2647  *
2648  * Also serves as futex trylock_pi()'ing, and due semantics.
2649  */
2650 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2651                          ktime_t *time, int trylock)
2652 {
2653         struct hrtimer_sleeper timeout, *to = NULL;
2654         struct futex_pi_state *pi_state = NULL;
2655         struct rt_mutex_waiter rt_waiter;
2656         struct futex_hash_bucket *hb;
2657         struct futex_q q = futex_q_init;
2658         int res, ret;
2659
2660         if (!IS_ENABLED(CONFIG_FUTEX_PI))
2661                 return -ENOSYS;
2662
2663         if (refill_pi_state_cache())
2664                 return -ENOMEM;
2665
2666         if (time) {
2667                 to = &timeout;
2668                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2669                                       HRTIMER_MODE_ABS);
2670                 hrtimer_init_sleeper(to, current);
2671                 hrtimer_set_expires(&to->timer, *time);
2672         }
2673
2674 retry:
2675         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2676         if (unlikely(ret != 0))
2677                 goto out;
2678
2679 retry_private:
2680         hb = queue_lock(&q);
2681
2682         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2683         if (unlikely(ret)) {
2684                 /*
2685                  * Atomic work succeeded and we got the lock,
2686                  * or failed. Either way, we do _not_ block.
2687                  */
2688                 switch (ret) {
2689                 case 1:
2690                         /* We got the lock. */
2691                         ret = 0;
2692                         goto out_unlock_put_key;
2693                 case -EFAULT:
2694                         goto uaddr_faulted;
2695                 case -EAGAIN:
2696                         /*
2697                          * Two reasons for this:
2698                          * - Task is exiting and we just wait for the
2699                          *   exit to complete.
2700                          * - The user space value changed.
2701                          */
2702                         queue_unlock(hb);
2703                         put_futex_key(&q.key);
2704                         cond_resched();
2705                         goto retry;
2706                 default:
2707                         goto out_unlock_put_key;
2708                 }
2709         }
2710
2711         WARN_ON(!q.pi_state);
2712
2713         /*
2714          * Only actually queue now that the atomic ops are done:
2715          */
2716         __queue_me(&q, hb);
2717
2718         if (trylock) {
2719                 ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
2720                 /* Fixup the trylock return value: */
2721                 ret = ret ? 0 : -EWOULDBLOCK;
2722                 goto no_block;
2723         }
2724
2725         rt_mutex_init_waiter(&rt_waiter);
2726
2727         /*
2728          * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
2729          * hold it while doing rt_mutex_start_proxy(), because then it will
2730          * include hb->lock in the blocking chain, even through we'll not in
2731          * fact hold it while blocking. This will lead it to report -EDEADLK
2732          * and BUG when futex_unlock_pi() interleaves with this.
2733          *
2734          * Therefore acquire wait_lock while holding hb->lock, but drop the
2735          * latter before calling rt_mutex_start_proxy_lock(). This still fully
2736          * serializes against futex_unlock_pi() as that does the exact same
2737          * lock handoff sequence.
2738          */
2739         raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
2740         spin_unlock(q.lock_ptr);
2741         ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
2742         raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
2743
2744         if (ret) {
2745                 if (ret == 1)
2746                         ret = 0;
2747
2748                 spin_lock(q.lock_ptr);
2749                 goto no_block;
2750         }
2751
2752
2753         if (unlikely(to))
2754                 hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
2755
2756         ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
2757
2758         spin_lock(q.lock_ptr);
2759         /*
2760          * If we failed to acquire the lock (signal/timeout), we must
2761          * first acquire the hb->lock before removing the lock from the
2762          * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
2763          * wait lists consistent.
2764          *
2765          * In particular; it is important that futex_unlock_pi() can not
2766          * observe this inconsistency.
2767          */
2768         if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
2769                 ret = 0;
2770
2771 no_block:
2772         /*
2773          * Fixup the pi_state owner and possibly acquire the lock if we
2774          * haven't already.
2775          */
2776         res = fixup_owner(uaddr, &q, !ret);
2777         /*
2778          * If fixup_owner() returned an error, proprogate that.  If it acquired
2779          * the lock, clear our -ETIMEDOUT or -EINTR.
2780          */
2781         if (res)
2782                 ret = (res < 0) ? res : 0;
2783
2784         /*
2785          * If fixup_owner() faulted and was unable to handle the fault, unlock
2786          * it and return the fault to userspace.
2787          */
2788         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
2789                 pi_state = q.pi_state;
2790                 get_pi_state(pi_state);
2791         }
2792
2793         /* Unqueue and drop the lock */
2794         unqueue_me_pi(&q);
2795
2796         if (pi_state) {
2797                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
2798                 put_pi_state(pi_state);
2799         }
2800
2801         goto out_put_key;
2802
2803 out_unlock_put_key:
2804         queue_unlock(hb);
2805
2806 out_put_key:
2807         put_futex_key(&q.key);
2808 out:
2809         if (to) {
2810                 hrtimer_cancel(&to->timer);
2811                 destroy_hrtimer_on_stack(&to->timer);
2812         }
2813         return ret != -EINTR ? ret : -ERESTARTNOINTR;
2814
2815 uaddr_faulted:
2816         queue_unlock(hb);
2817
2818         ret = fault_in_user_writeable(uaddr);
2819         if (ret)
2820                 goto out_put_key;
2821
2822         if (!(flags & FLAGS_SHARED))
2823                 goto retry_private;
2824
2825         put_futex_key(&q.key);
2826         goto retry;
2827 }
2828
2829 /*
2830  * Userspace attempted a TID -> 0 atomic transition, and failed.
2831  * This is the in-kernel slowpath: we look up the PI state (if any),
2832  * and do the rt-mutex unlock.
2833  */
2834 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2835 {
2836         u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
2837         union futex_key key = FUTEX_KEY_INIT;
2838         struct futex_hash_bucket *hb;
2839         struct futex_q *top_waiter;
2840         int ret;
2841
2842         if (!IS_ENABLED(CONFIG_FUTEX_PI))
2843                 return -ENOSYS;
2844
2845 retry:
2846         if (get_user(uval, uaddr))
2847                 return -EFAULT;
2848         /*
2849          * We release only a lock we actually own:
2850          */
2851         if ((uval & FUTEX_TID_MASK) != vpid)
2852                 return -EPERM;
2853
2854         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2855         if (ret)
2856                 return ret;
2857
2858         hb = hash_futex(&key);
2859         spin_lock(&hb->lock);
2860
2861         /*
2862          * Check waiters first. We do not trust user space values at
2863          * all and we at least want to know if user space fiddled
2864          * with the futex value instead of blindly unlocking.
2865          */
2866         top_waiter = futex_top_waiter(hb, &key);
2867         if (top_waiter) {
2868                 struct futex_pi_state *pi_state = top_waiter->pi_state;
2869
2870                 ret = -EINVAL;
2871                 if (!pi_state)
2872                         goto out_unlock;
2873
2874                 /*
2875                  * If current does not own the pi_state then the futex is
2876                  * inconsistent and user space fiddled with the futex value.
2877                  */
2878                 if (pi_state->owner != current)
2879                         goto out_unlock;
2880
2881                 get_pi_state(pi_state);
2882                 /*
2883                  * By taking wait_lock while still holding hb->lock, we ensure
2884                  * there is no point where we hold neither; and therefore
2885                  * wake_futex_pi() must observe a state consistent with what we
2886                  * observed.
2887                  */
2888                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2889                 spin_unlock(&hb->lock);
2890
2891                 /* drops pi_state->pi_mutex.wait_lock */
2892                 ret = wake_futex_pi(uaddr, uval, pi_state);
2893
2894                 put_pi_state(pi_state);
2895
2896                 /*
2897                  * Success, we're done! No tricky corner cases.
2898                  */
2899                 if (!ret)
2900                         goto out_putkey;
2901                 /*
2902                  * The atomic access to the futex value generated a
2903                  * pagefault, so retry the user-access and the wakeup:
2904                  */
2905                 if (ret == -EFAULT)
2906                         goto pi_faulted;
2907                 /*
2908                  * A unconditional UNLOCK_PI op raced against a waiter
2909                  * setting the FUTEX_WAITERS bit. Try again.
2910                  */
2911                 if (ret == -EAGAIN) {
2912                         put_futex_key(&key);
2913                         goto retry;
2914                 }
2915                 /*
2916                  * wake_futex_pi has detected invalid state. Tell user
2917                  * space.
2918                  */
2919                 goto out_putkey;
2920         }
2921
2922         /*
2923          * We have no kernel internal state, i.e. no waiters in the
2924          * kernel. Waiters which are about to queue themselves are stuck
2925          * on hb->lock. So we can safely ignore them. We do neither
2926          * preserve the WAITERS bit not the OWNER_DIED one. We are the
2927          * owner.
2928          */
2929         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
2930                 spin_unlock(&hb->lock);
2931                 goto pi_faulted;
2932         }
2933
2934         /*
2935          * If uval has changed, let user space handle it.
2936          */
2937         ret = (curval == uval) ? 0 : -EAGAIN;
2938
2939 out_unlock:
2940         spin_unlock(&hb->lock);
2941 out_putkey:
2942         put_futex_key(&key);
2943         return ret;
2944
2945 pi_faulted:
2946         put_futex_key(&key);
2947
2948         ret = fault_in_user_writeable(uaddr);
2949         if (!ret)
2950                 goto retry;
2951
2952         return ret;
2953 }
2954
2955 /**
2956  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2957  * @hb:         the hash_bucket futex_q was original enqueued on
2958  * @q:          the futex_q woken while waiting to be requeued
2959  * @key2:       the futex_key of the requeue target futex
2960  * @timeout:    the timeout associated with the wait (NULL if none)
2961  *
2962  * Detect if the task was woken on the initial futex as opposed to the requeue
2963  * target futex.  If so, determine if it was a timeout or a signal that caused
2964  * the wakeup and return the appropriate error code to the caller.  Must be
2965  * called with the hb lock held.
2966  *
2967  * Return:
2968  *  -  0 = no early wakeup detected;
2969  *  - <0 = -ETIMEDOUT or -ERESTARTNOINTR
2970  */
2971 static inline
2972 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2973                                    struct futex_q *q, union futex_key *key2,
2974                                    struct hrtimer_sleeper *timeout)
2975 {
2976         int ret = 0;
2977
2978         /*
2979          * With the hb lock held, we avoid races while we process the wakeup.
2980          * We only need to hold hb (and not hb2) to ensure atomicity as the
2981          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2982          * It can't be requeued from uaddr2 to something else since we don't
2983          * support a PI aware source futex for requeue.
2984          */
2985         if (!match_futex(&q->key, key2)) {
2986                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2987                 /*
2988                  * We were woken prior to requeue by a timeout or a signal.
2989                  * Unqueue the futex_q and determine which it was.
2990                  */
2991                 plist_del(&q->list, &hb->chain);
2992                 hb_waiters_dec(hb);
2993
2994                 /* Handle spurious wakeups gracefully */
2995                 ret = -EWOULDBLOCK;
2996                 if (timeout && !timeout->task)
2997                         ret = -ETIMEDOUT;
2998                 else if (signal_pending(current))
2999                         ret = -ERESTARTNOINTR;
3000         }
3001         return ret;
3002 }
3003
3004 /**
3005  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
3006  * @uaddr:      the futex we initially wait on (non-pi)
3007  * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
3008  *              the same type, no requeueing from private to shared, etc.
3009  * @val:        the expected value of uaddr
3010  * @abs_time:   absolute timeout
3011  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
3012  * @uaddr2:     the pi futex we will take prior to returning to user-space
3013  *
3014  * The caller will wait on uaddr and will be requeued by futex_requeue() to
3015  * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
3016  * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
3017  * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
3018  * without one, the pi logic would not know which task to boost/deboost, if
3019  * there was a need to.
3020  *
3021  * We call schedule in futex_wait_queue_me() when we enqueue and return there
3022  * via the following--
3023  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
3024  * 2) wakeup on uaddr2 after a requeue
3025  * 3) signal
3026  * 4) timeout
3027  *
3028  * If 3, cleanup and return -ERESTARTNOINTR.
3029  *
3030  * If 2, we may then block on trying to take the rt_mutex and return via:
3031  * 5) successful lock
3032  * 6) signal
3033  * 7) timeout
3034  * 8) other lock acquisition failure
3035  *
3036  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
3037  *
3038  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
3039  *
3040  * Return:
3041  *  -  0 - On success;
3042  *  - <0 - On error
3043  */
3044 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
3045                                  u32 val, ktime_t *abs_time, u32 bitset,
3046                                  u32 __user *uaddr2)
3047 {
3048         struct hrtimer_sleeper timeout, *to = NULL;
3049         struct futex_pi_state *pi_state = NULL;
3050         struct rt_mutex_waiter rt_waiter;
3051         struct futex_hash_bucket *hb;
3052         union futex_key key2 = FUTEX_KEY_INIT;
3053         struct futex_q q = futex_q_init;
3054         int res, ret;
3055
3056         if (!IS_ENABLED(CONFIG_FUTEX_PI))
3057                 return -ENOSYS;
3058
3059         if (uaddr == uaddr2)
3060                 return -EINVAL;
3061
3062         if (!bitset)
3063                 return -EINVAL;
3064
3065         if (abs_time) {
3066                 to = &timeout;
3067                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
3068                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
3069                                       HRTIMER_MODE_ABS);
3070                 hrtimer_init_sleeper(to, current);
3071                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
3072                                              current->timer_slack_ns);
3073         }
3074
3075         /*
3076          * The waiter is allocated on our stack, manipulated by the requeue
3077          * code while we sleep on uaddr.
3078          */
3079         rt_mutex_init_waiter(&rt_waiter);
3080
3081         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
3082         if (unlikely(ret != 0))
3083                 goto out;
3084
3085         q.bitset = bitset;
3086         q.rt_waiter = &rt_waiter;
3087         q.requeue_pi_key = &key2;
3088
3089         /*
3090          * Prepare to wait on uaddr. On success, increments q.key (key1) ref
3091          * count.
3092          */
3093         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
3094         if (ret)
3095                 goto out_key2;
3096
3097         /*
3098          * The check above which compares uaddrs is not sufficient for
3099          * shared futexes. We need to compare the keys:
3100          */
3101         if (match_futex(&q.key, &key2)) {
3102                 queue_unlock(hb);
3103                 ret = -EINVAL;
3104                 goto out_put_keys;
3105         }
3106
3107         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
3108         futex_wait_queue_me(hb, &q, to);
3109
3110         spin_lock(&hb->lock);
3111         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
3112         spin_unlock(&hb->lock);
3113         if (ret)
3114                 goto out_put_keys;
3115
3116         /*
3117          * In order for us to be here, we know our q.key == key2, and since
3118          * we took the hb->lock above, we also know that futex_requeue() has
3119          * completed and we no longer have to concern ourselves with a wakeup
3120          * race with the atomic proxy lock acquisition by the requeue code. The
3121          * futex_requeue dropped our key1 reference and incremented our key2
3122          * reference count.
3123          */
3124
3125         /* Check if the requeue code acquired the second futex for us. */
3126         if (!q.rt_waiter) {
3127                 /*
3128                  * Got the lock. We might not be the anticipated owner if we
3129                  * did a lock-steal - fix up the PI-state in that case.
3130                  */
3131                 if (q.pi_state && (q.pi_state->owner != current)) {
3132                         spin_lock(q.lock_ptr);
3133                         ret = fixup_pi_state_owner(uaddr2, &q, current);
3134                         if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3135                                 pi_state = q.pi_state;
3136                                 get_pi_state(pi_state);
3137                         }
3138                         /*
3139                          * Drop the reference to the pi state which
3140                          * the requeue_pi() code acquired for us.
3141                          */
3142                         put_pi_state(q.pi_state);
3143                         spin_unlock(q.lock_ptr);
3144                 }
3145         } else {
3146                 struct rt_mutex *pi_mutex;
3147
3148                 /*
3149                  * We have been woken up by futex_unlock_pi(), a timeout, or a
3150                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
3151                  * the pi_state.
3152                  */
3153                 WARN_ON(!q.pi_state);
3154                 pi_mutex = &q.pi_state->pi_mutex;
3155                 ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
3156
3157                 spin_lock(q.lock_ptr);
3158                 if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
3159                         ret = 0;
3160
3161                 debug_rt_mutex_free_waiter(&rt_waiter);
3162                 /*
3163                  * Fixup the pi_state owner and possibly acquire the lock if we
3164                  * haven't already.
3165                  */
3166                 res = fixup_owner(uaddr2, &q, !ret);
3167                 /*
3168                  * If fixup_owner() returned an error, proprogate that.  If it
3169                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
3170                  */
3171                 if (res)
3172                         ret = (res < 0) ? res : 0;
3173
3174                 /*
3175                  * If fixup_pi_state_owner() faulted and was unable to handle
3176                  * the fault, unlock the rt_mutex and return the fault to
3177                  * userspace.
3178                  */
3179                 if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3180                         pi_state = q.pi_state;
3181                         get_pi_state(pi_state);
3182                 }
3183
3184                 /* Unqueue and drop the lock. */
3185                 unqueue_me_pi(&q);
3186         }
3187
3188         if (pi_state) {
3189                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
3190                 put_pi_state(pi_state);
3191         }
3192
3193         if (ret == -EINTR) {
3194                 /*
3195                  * We've already been requeued, but cannot restart by calling
3196                  * futex_lock_pi() directly. We could restart this syscall, but
3197                  * it would detect that the user space "val" changed and return
3198                  * -EWOULDBLOCK.  Save the overhead of the restart and return
3199                  * -EWOULDBLOCK directly.
3200                  */
3201                 ret = -EWOULDBLOCK;
3202         }
3203
3204 out_put_keys:
3205         put_futex_key(&q.key);
3206 out_key2:
3207         put_futex_key(&key2);
3208
3209 out:
3210         if (to) {
3211                 hrtimer_cancel(&to->timer);
3212                 destroy_hrtimer_on_stack(&to->timer);
3213         }
3214         return ret;
3215 }
3216
3217 /*
3218  * Support for robust futexes: the kernel cleans up held futexes at
3219  * thread exit time.
3220  *
3221  * Implementation: user-space maintains a per-thread list of locks it
3222  * is holding. Upon do_exit(), the kernel carefully walks this list,
3223  * and marks all locks that are owned by this thread with the
3224  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
3225  * always manipulated with the lock held, so the list is private and
3226  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
3227  * field, to allow the kernel to clean up if the thread dies after
3228  * acquiring the lock, but just before it could have added itself to
3229  * the list. There can only be one such pending lock.
3230  */
3231
3232 /**
3233  * sys_set_robust_list() - Set the robust-futex list head of a task
3234  * @head:       pointer to the list-head
3235  * @len:        length of the list-head, as userspace expects
3236  */
3237 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
3238                 size_t, len)
3239 {
3240         if (!futex_cmpxchg_enabled)
3241                 return -ENOSYS;
3242         /*
3243          * The kernel knows only one size for now:
3244          */
3245         if (unlikely(len != sizeof(*head)))
3246                 return -EINVAL;
3247
3248         current->robust_list = head;
3249
3250         return 0;
3251 }
3252
3253 /**
3254  * sys_get_robust_list() - Get the robust-futex list head of a task
3255  * @pid:        pid of the process [zero for current task]
3256  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
3257  * @len_ptr:    pointer to a length field, the kernel fills in the header size
3258  */
3259 SYSCALL_DEFINE3(get_robust_list, int, pid,
3260                 struct robust_list_head __user * __user *, head_ptr,
3261                 size_t __user *, len_ptr)
3262 {
3263         struct robust_list_head __user *head;
3264         unsigned long ret;
3265         struct task_struct *p;
3266
3267         if (!futex_cmpxchg_enabled)
3268                 return -ENOSYS;
3269
3270         rcu_read_lock();
3271
3272         ret = -ESRCH;
3273         if (!pid)
3274                 p = current;
3275         else {
3276                 p = find_task_by_vpid(pid);
3277                 if (!p)
3278                         goto err_unlock;
3279         }
3280
3281         ret = -EPERM;
3282         if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
3283                 goto err_unlock;
3284
3285         head = p->robust_list;
3286         rcu_read_unlock();
3287
3288         if (put_user(sizeof(*head), len_ptr))
3289                 return -EFAULT;
3290         return put_user(head, head_ptr);
3291
3292 err_unlock:
3293         rcu_read_unlock();
3294
3295         return ret;
3296 }
3297
3298 /*
3299  * Process a futex-list entry, check whether it's owned by the
3300  * dying task, and do notification if so:
3301  */
3302 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
3303 {
3304         u32 uval, uninitialized_var(nval), mval;
3305
3306 retry:
3307         if (get_user(uval, uaddr))
3308                 return -1;
3309
3310         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
3311                 /*
3312                  * Ok, this dying thread is truly holding a futex
3313                  * of interest. Set the OWNER_DIED bit atomically
3314                  * via cmpxchg, and if the value had FUTEX_WAITERS
3315                  * set, wake up a waiter (if any). (We have to do a
3316                  * futex_wake() even if OWNER_DIED is already set -
3317                  * to handle the rare but possible case of recursive
3318                  * thread-death.) The rest of the cleanup is done in
3319                  * userspace.
3320                  */
3321                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
3322                 /*
3323                  * We are not holding a lock here, but we want to have
3324                  * the pagefault_disable/enable() protection because
3325                  * we want to handle the fault gracefully. If the
3326                  * access fails we try to fault in the futex with R/W
3327                  * verification via get_user_pages. get_user() above
3328                  * does not guarantee R/W access. If that fails we
3329                  * give up and leave the futex locked.
3330                  */
3331                 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
3332                         if (fault_in_user_writeable(uaddr))
3333                                 return -1;
3334                         goto retry;
3335                 }
3336                 if (nval != uval)
3337                         goto retry;
3338
3339                 /*
3340                  * Wake robust non-PI futexes here. The wakeup of
3341                  * PI futexes happens in exit_pi_state():
3342                  */
3343                 if (!pi && (uval & FUTEX_WAITERS))
3344                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3345         }
3346         return 0;
3347 }
3348
3349 /*
3350  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3351  */
3352 static inline int fetch_robust_entry(struct robust_list __user **entry,
3353                                      struct robust_list __user * __user *head,
3354                                      unsigned int *pi)
3355 {
3356         unsigned long uentry;
3357
3358         if (get_user(uentry, (unsigned long __user *)head))
3359                 return -EFAULT;
3360
3361         *entry = (void __user *)(uentry & ~1UL);
3362         *pi = uentry & 1;
3363
3364         return 0;
3365 }
3366
3367 /*
3368  * Walk curr->robust_list (very carefully, it's a userspace list!)
3369  * and mark any locks found there dead, and notify any waiters.
3370  *
3371  * We silently return on any sign of list-walking problem.
3372  */
3373 void exit_robust_list(struct task_struct *curr)
3374 {
3375         struct robust_list_head __user *head = curr->robust_list;
3376         struct robust_list __user *entry, *next_entry, *pending;
3377         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3378         unsigned int uninitialized_var(next_pi);
3379         unsigned long futex_offset;
3380         int rc;
3381
3382         if (!futex_cmpxchg_enabled)
3383                 return;
3384
3385         /*
3386          * Fetch the list head (which was registered earlier, via
3387          * sys_set_robust_list()):
3388          */
3389         if (fetch_robust_entry(&entry, &head->list.next, &pi))
3390                 return;
3391         /*
3392          * Fetch the relative futex offset:
3393          */
3394         if (get_user(futex_offset, &head->futex_offset))
3395                 return;
3396         /*
3397          * Fetch any possibly pending lock-add first, and handle it
3398          * if it exists:
3399          */
3400         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3401                 return;
3402
3403         next_entry = NULL;      /* avoid warning with gcc */
3404         while (entry != &head->list) {
3405                 /*
3406                  * Fetch the next entry in the list before calling
3407                  * handle_futex_death:
3408                  */
3409                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3410                 /*
3411                  * A pending lock might already be on the list, so
3412                  * don't process it twice:
3413                  */
3414                 if (entry != pending)
3415                         if (handle_futex_death((void __user *)entry + futex_offset,
3416                                                 curr, pi))
3417                                 return;
3418                 if (rc)
3419                         return;
3420                 entry = next_entry;
3421                 pi = next_pi;
3422                 /*
3423                  * Avoid excessively long or circular lists:
3424                  */
3425                 if (!--limit)
3426                         break;
3427
3428                 cond_resched();
3429         }
3430
3431         if (pending)
3432                 handle_futex_death((void __user *)pending + futex_offset,
3433                                    curr, pip);
3434 }
3435
3436 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3437                 u32 __user *uaddr2, u32 val2, u32 val3)
3438 {
3439         int cmd = op & FUTEX_CMD_MASK;
3440         unsigned int flags = 0;
3441
3442         if (!(op & FUTEX_PRIVATE_FLAG))
3443                 flags |= FLAGS_SHARED;
3444
3445         if (op & FUTEX_CLOCK_REALTIME) {
3446                 flags |= FLAGS_CLOCKRT;
3447                 if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
3448                     cmd != FUTEX_WAIT_REQUEUE_PI)
3449                         return -ENOSYS;
3450         }
3451
3452         switch (cmd) {
3453         case FUTEX_LOCK_PI:
3454         case FUTEX_UNLOCK_PI:
3455         case FUTEX_TRYLOCK_PI:
3456         case FUTEX_WAIT_REQUEUE_PI:
3457         case FUTEX_CMP_REQUEUE_PI:
3458                 if (!futex_cmpxchg_enabled)
3459                         return -ENOSYS;
3460         }
3461
3462         switch (cmd) {
3463         case FUTEX_WAIT:
3464                 val3 = FUTEX_BITSET_MATCH_ANY;
3465         case FUTEX_WAIT_BITSET:
3466                 return futex_wait(uaddr, flags, val, timeout, val3);
3467         case FUTEX_WAKE:
3468                 val3 = FUTEX_BITSET_MATCH_ANY;
3469         case FUTEX_WAKE_BITSET:
3470                 return futex_wake(uaddr, flags, val, val3);
3471         case FUTEX_REQUEUE:
3472                 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3473         case FUTEX_CMP_REQUEUE:
3474                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3475         case FUTEX_WAKE_OP:
3476                 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3477         case FUTEX_LOCK_PI:
3478                 return futex_lock_pi(uaddr, flags, timeout, 0);
3479         case FUTEX_UNLOCK_PI:
3480                 return futex_unlock_pi(uaddr, flags);
3481         case FUTEX_TRYLOCK_PI:
3482                 return futex_lock_pi(uaddr, flags, NULL, 1);
3483         case FUTEX_WAIT_REQUEUE_PI:
3484                 val3 = FUTEX_BITSET_MATCH_ANY;
3485                 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3486                                              uaddr2);
3487         case FUTEX_CMP_REQUEUE_PI:
3488                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3489         }
3490         return -ENOSYS;
3491 }
3492
3493
3494 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3495                 struct timespec __user *, utime, u32 __user *, uaddr2,
3496                 u32, val3)
3497 {
3498         struct timespec ts;
3499         ktime_t t, *tp = NULL;
3500         u32 val2 = 0;
3501         int cmd = op & FUTEX_CMD_MASK;
3502
3503         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3504                       cmd == FUTEX_WAIT_BITSET ||
3505                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
3506                 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3507                         return -EFAULT;
3508                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3509                         return -EFAULT;
3510                 if (!timespec_valid(&ts))
3511                         return -EINVAL;
3512
3513                 t = timespec_to_ktime(ts);
3514                 if (cmd == FUTEX_WAIT)
3515                         t = ktime_add_safe(ktime_get(), t);
3516                 tp = &t;
3517         }
3518         /*
3519          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3520          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3521          */
3522         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3523             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3524                 val2 = (u32) (unsigned long) utime;
3525
3526         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3527 }
3528
3529 static void __init futex_detect_cmpxchg(void)
3530 {
3531 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3532         u32 curval;
3533
3534         /*
3535          * This will fail and we want it. Some arch implementations do
3536          * runtime detection of the futex_atomic_cmpxchg_inatomic()
3537          * functionality. We want to know that before we call in any
3538          * of the complex code paths. Also we want to prevent
3539          * registration of robust lists in that case. NULL is
3540          * guaranteed to fault and we get -EFAULT on functional
3541          * implementation, the non-functional ones will return
3542          * -ENOSYS.
3543          */
3544         if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3545                 futex_cmpxchg_enabled = 1;
3546 #endif
3547 }
3548
3549 static int __init futex_init(void)
3550 {
3551         unsigned int futex_shift;
3552         unsigned long i;
3553
3554 #if CONFIG_BASE_SMALL
3555         futex_hashsize = 16;
3556 #else
3557         futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3558 #endif
3559
3560         futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3561                                                futex_hashsize, 0,
3562                                                futex_hashsize < 256 ? HASH_SMALL : 0,
3563                                                &futex_shift, NULL,
3564                                                futex_hashsize, futex_hashsize);
3565         futex_hashsize = 1UL << futex_shift;
3566
3567         futex_detect_cmpxchg();
3568
3569         for (i = 0; i < futex_hashsize; i++) {
3570                 atomic_set(&futex_queues[i].waiters, 0);
3571                 plist_head_init(&futex_queues[i].chain);
3572                 spin_lock_init(&futex_queues[i].lock);
3573         }
3574
3575         return 0;
3576 }
3577 core_initcall(futex_init);