kernel/fork.c

   1 /*
   2  *  linux/kernel/fork.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 /*
   8  *  'fork.c' contains the help-routines for the 'fork' system call
   9  * (see also entry.S and others).
  10  * Fork is rather simple, once you get the hang of it, but the memory
  11  * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
  12  */
  13
  14 #include <linux/slab.h>
  15 #include <linux/sched/autogroup.h>
  16 #include <linux/sched/mm.h>
  17 #include <linux/sched/coredump.h>
  18 #include <linux/sched/user.h>
  19 #include <linux/sched/numa_balancing.h>
  20 #include <linux/sched/stat.h>
  21 #include <linux/sched/task.h>
  22 #include <linux/sched/task_stack.h>
  23 #include <linux/sched/cputime.h>
  24 #include <linux/rtmutex.h>
  25 #include <linux/init.h>
  26 #include <linux/unistd.h>
  27 #include <linux/module.h>
  28 #include <linux/vmalloc.h>
  29 #include <linux/completion.h>
  30 #include <linux/personality.h>
  31 #include <linux/mempolicy.h>
  32 #include <linux/sem.h>
  33 #include <linux/file.h>
  34 #include <linux/fdtable.h>
  35 #include <linux/iocontext.h>
  36 #include <linux/key.h>
  37 #include <linux/binfmts.h>
  38 #include <linux/mman.h>
  39 #include <linux/mmu_notifier.h>
  40 #include <linux/hmm.h>
  41 #include <linux/fs.h>
  42 #include <linux/mm.h>
  43 #include <linux/vmacache.h>
  44 #include <linux/nsproxy.h>
  45 #include <linux/capability.h>
  46 #include <linux/cpu.h>
  47 #include <linux/cgroup.h>
  48 #include <linux/security.h>
  49 #include <linux/hugetlb.h>
  50 #include <linux/seccomp.h>
  51 #include <linux/swap.h>
  52 #include <linux/syscalls.h>
  53 #include <linux/jiffies.h>
  54 #include <linux/futex.h>
  55 #include <linux/compat.h>
  56 #include <linux/kthread.h>
  57 #include <linux/task_io_accounting_ops.h>
  58 #include <linux/rcupdate.h>
  59 #include <linux/ptrace.h>
  60 #include <linux/mount.h>
  61 #include <linux/audit.h>
  62 #include <linux/memcontrol.h>
  63 #include <linux/ftrace.h>
  64 #include <linux/proc_fs.h>
  65 #include <linux/profile.h>
  66 #include <linux/rmap.h>
  67 #include <linux/ksm.h>
  68 #include <linux/acct.h>
  69 #include <linux/userfaultfd_k.h>
  70 #include <linux/tsacct_kern.h>
  71 #include <linux/cn_proc.h>
  72 #include <linux/freezer.h>
  73 #include <linux/delayacct.h>
  74 #include <linux/taskstats_kern.h>
  75 #include <linux/random.h>
  76 #include <linux/tty.h>
  77 #include <linux/blkdev.h>
  78 #include <linux/fs_struct.h>
  79 #include <linux/magic.h>
  80 #include <linux/perf_event.h>
  81 #include <linux/posix-timers.h>
  82 #include <linux/user-return-notifier.h>
  83 #include <linux/oom.h>
  84 #include <linux/khugepaged.h>
  85 #include <linux/signalfd.h>
  86 #include <linux/uprobes.h>
  87 #include <linux/aio.h>
  88 #include <linux/compiler.h>
  89 #include <linux/sysctl.h>
  90 #include <linux/kcov.h>
  91 #include <linux/livepatch.h>
  92 #include <linux/thread_info.h>
  93 #include <linux/stackleak.h>
  94
  95 #include <asm/pgtable.h>
  96 #include <asm/pgalloc.h>
  97 #include <linux/uaccess.h>
  98 #include <asm/mmu_context.h>
  99 #include <asm/cacheflush.h>
 100 #include <asm/tlbflush.h>
 101
 102 #include <trace/events/sched.h>
 103
 104 #define CREATE_TRACE_POINTS
 105 #include <trace/events/task.h>
 106
 107 /*
 108  * Minimum number of threads to boot the kernel
 109  */
 110 #define MIN_THREADS 20
 111
 112 /*
 113  * Maximum number of threads
 114  */
 115 #define MAX_THREADS FUTEX_TID_MASK
 116
 117 /*
 118  * Protected counters by write_lock_irq(&tasklist_lock)
 119  */
 120 unsigned long total_forks;      /* Handle normal Linux uptimes. */
 121 int nr_threads;                 /* The idle threads do not count.. */
 122
 123 int max_threads;                /* tunable limit on nr_threads */
 124
 125 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
 126
 127 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
 128
 129 #ifdef CONFIG_PROVE_RCU
 130 int lockdep_tasklist_lock_is_held(void)
 131 {
 132         return lockdep_is_held(&tasklist_lock);
 133 }
 134 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
 135 #endif /* #ifdef CONFIG_PROVE_RCU */
 136
 137 int nr_processes(void)
 138 {
 139         int cpu;
 140         int total = 0;
 141
 142         for_each_possible_cpu(cpu)
 143                 total += per_cpu(process_counts, cpu);
 144
 145         return total;
 146 }
 147
 148 void __weak arch_release_task_struct(struct task_struct *tsk)
 149 {
 150 }
 151
 152 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 153 static struct kmem_cache *task_struct_cachep;
 154
 155 static inline struct task_struct *alloc_task_struct_node(int node)
 156 {
 157         return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
 158 }
 159
 160 static inline void free_task_struct(struct task_struct *tsk)
 161 {
 162         kmem_cache_free(task_struct_cachep, tsk);
 163 }
 164 #endif
 165
 166 #ifndef CONFIG_ARCH_THREAD_STACK_ALLOCATOR
 167
 168 /*
 169  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
 170  * kmemcache based allocator.
 171  */
 172 # if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)
 173
 174 #ifdef CONFIG_VMAP_STACK
 175 /*
 176  * vmalloc() is a bit slow, and calling vfree() enough times will force a TLB
 177  * flush.  Try to minimize the number of calls by caching stacks.
 178  */
 179 #define NR_CACHED_STACKS 2
 180 static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
 181
 182 static int free_vm_stack_cache(unsigned int cpu)
 183 {
 184         struct vm_struct **cached_vm_stacks = per_cpu_ptr(cached_stacks, cpu);
 185         int i;
 186
 187         for (i = 0; i < NR_CACHED_STACKS; i++) {
 188                 struct vm_struct *vm_stack = cached_vm_stacks[i];
 189
 190                 if (!vm_stack)
 191                         continue;
 192
 193                 vfree(vm_stack->addr);
 194                 cached_vm_stacks[i] = NULL;
 195         }
 196
 197         return 0;
 198 }
 199 #endif
 200
 201 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 202 {
 203 #ifdef CONFIG_VMAP_STACK
 204         void *stack;
 205         int i;
 206
 207         for (i = 0; i < NR_CACHED_STACKS; i++) {
 208                 struct vm_struct *s;
 209
 210                 s = this_cpu_xchg(cached_stacks[i], NULL);
 211
 212                 if (!s)
 213                         continue;
 214
 215                 /* Clear stale pointers from reused stack. */
 216                 memset(s->addr, 0, THREAD_SIZE);
 217
 218                 tsk->stack_vm_area = s;
 219                 tsk->stack = s->addr;
 220                 return s->addr;
 221         }
 222
 223         /*
 224          * Allocated stacks are cached and later reused by new threads,
 225          * so memcg accounting is performed manually on assigning/releasing
 226          * stacks to tasks. Drop __GFP_ACCOUNT.
 227          */
 228         stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
 229                                      VMALLOC_START, VMALLOC_END,
 230                                      THREADINFO_GFP & ~__GFP_ACCOUNT,
 231                                      PAGE_KERNEL,
 232                                      0, node, __builtin_return_address(0));
 233
 234         /*
 235          * We can't call find_vm_area() in interrupt context, and
 236          * free_thread_stack() can be called in interrupt context,
 237          * so cache the vm_struct.
 238          */
 239         if (stack) {
 240                 tsk->stack_vm_area = find_vm_area(stack);
 241                 tsk->stack = stack;
 242         }
 243         return stack;
 244 #else
 245         struct page *page = alloc_pages_node(node, THREADINFO_GFP,
 246                                              THREAD_SIZE_ORDER);
 247
 248         return page ? page_address(page) : NULL;
 249 #endif
 250 }
 251
 252 static inline void free_thread_stack(struct task_struct *tsk)
 253 {
 254 #ifdef CONFIG_VMAP_STACK
 255         struct vm_struct *vm = task_stack_vm_area(tsk);
 256
 257         if (vm) {
 258                 int i;
 259
 260                 for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
 261                         mod_memcg_page_state(vm->pages[i],
 262                                              MEMCG_KERNEL_STACK_KB,
 263                                              -(int)(PAGE_SIZE / 1024));
 264
 265                         memcg_kmem_uncharge(vm->pages[i], 0);
 266                 }
 267
 268                 for (i = 0; i < NR_CACHED_STACKS; i++) {
 269                         if (this_cpu_cmpxchg(cached_stacks[i],
 270                                         NULL, tsk->stack_vm_area) != NULL)
 271                                 continue;
 272
 273                         return;
 274                 }
 275
 276                 vfree_atomic(tsk->stack);
 277                 return;
 278         }
 279 #endif
 280
 281         __free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER);
 282 }
 283 # else
 284 static struct kmem_cache *thread_stack_cache;
 285
 286 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
 287                                                   int node)
 288 {
 289         unsigned long *stack;
 290         stack = kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
 291         tsk->stack = stack;
 292         return stack;
 293 }
 294
 295 static void free_thread_stack(struct task_struct *tsk)
 296 {
 297         kmem_cache_free(thread_stack_cache, tsk->stack);
 298 }
 299
 300 void thread_stack_cache_init(void)
 301 {
 302         thread_stack_cache = kmem_cache_create_usercopy("thread_stack",
 303                                         THREAD_SIZE, THREAD_SIZE, 0, 0,
 304                                         THREAD_SIZE, NULL);
 305         BUG_ON(thread_stack_cache == NULL);
 306 }
 307 # endif
 308 #endif
 309
 310 /* SLAB cache for signal_struct structures (tsk->signal) */
 311 static struct kmem_cache *signal_cachep;
 312
 313 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 314 struct kmem_cache *sighand_cachep;
 315
 316 /* SLAB cache for files_struct structures (tsk->files) */
 317 struct kmem_cache *files_cachep;
 318
 319 /* SLAB cache for fs_struct structures (tsk->fs) */
 320 struct kmem_cache *fs_cachep;
 321
 322 /* SLAB cache for vm_area_struct structures */
 323 static struct kmem_cache *vm_area_cachep;
 324
 325 /* SLAB cache for mm_struct structures (tsk->mm) */
 326 static struct kmem_cache *mm_cachep;
 327
 328 struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
 329 {
 330         struct vm_area_struct *vma;
 331
 332         vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 333         if (vma)
 334                 vma_init(vma, mm);
 335         return vma;
 336 }
 337
 338 struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 339 {
 340         struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 341
 342         if (new) {
 343                 *new = *orig;
 344                 INIT_LIST_HEAD(&new->anon_vma_chain);
 345         }
 346         return new;
 347 }
 348
 349 void vm_area_free(struct vm_area_struct *vma)
 350 {
 351         kmem_cache_free(vm_area_cachep, vma);
 352 }
 353
 354 static void account_kernel_stack(struct task_struct *tsk, int account)
 355 {
 356         void *stack = task_stack_page(tsk);
 357         struct vm_struct *vm = task_stack_vm_area(tsk);
 358
 359         BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
 360
 361         if (vm) {
 362                 int i;
 363
 364                 BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
 365
 366                 for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
 367                         mod_zone_page_state(page_zone(vm->pages[i]),
 368                                             NR_KERNEL_STACK_KB,
 369                                             PAGE_SIZE / 1024 * account);
 370                 }
 371         } else {
 372                 /*
 373                  * All stack pages are in the same zone and belong to the
 374                  * same memcg.
 375                  */
 376                 struct page *first_page = virt_to_page(stack);
 377
 378                 mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
 379                                     THREAD_SIZE / 1024 * account);
 380
 381                 mod_memcg_page_state(first_page, MEMCG_KERNEL_STACK_KB,
 382                                      account * (THREAD_SIZE / 1024));
 383         }
 384 }
 385
 386 static int memcg_charge_kernel_stack(struct task_struct *tsk)
 387 {
 388 #ifdef CONFIG_VMAP_STACK
 389         struct vm_struct *vm = task_stack_vm_area(tsk);
 390         int ret;
 391
 392         if (vm) {
 393                 int i;
 394
 395                 for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
 396                         /*
 397                          * If memcg_kmem_charge() fails, page->mem_cgroup
 398                          * pointer is NULL, and both memcg_kmem_uncharge()
 399                          * and mod_memcg_page_state() in free_thread_stack()
 400                          * will ignore this page. So it's safe.
 401                          */
 402                         ret = memcg_kmem_charge(vm->pages[i], GFP_KERNEL, 0);
 403                         if (ret)
 404                                 return ret;
 405
 406                         mod_memcg_page_state(vm->pages[i],
 407                                              MEMCG_KERNEL_STACK_KB,
 408                                              PAGE_SIZE / 1024);
 409                 }
 410         }
 411 #endif
 412         return 0;
 413 }
 414
 415 static void release_task_stack(struct task_struct *tsk)
 416 {
 417         if (WARN_ON(tsk->state != TASK_DEAD))
 418                 return;  /* Better to leak the stack than to free prematurely */
 419
 420         account_kernel_stack(tsk, -1);
 421         free_thread_stack(tsk);
 422         tsk->stack = NULL;
 423 #ifdef CONFIG_VMAP_STACK
 424         tsk->stack_vm_area = NULL;
 425 #endif
 426 }
 427
 428 #ifdef CONFIG_THREAD_INFO_IN_TASK
 429 void put_task_stack(struct task_struct *tsk)
 430 {
 431         if (refcount_dec_and_test(&tsk->stack_refcount))
 432                 release_task_stack(tsk);
 433 }
 434 #endif
 435
 436 void free_task(struct task_struct *tsk)
 437 {
 438 #ifndef CONFIG_THREAD_INFO_IN_TASK
 439         /*
 440          * The task is finally done with both the stack and thread_info,
 441          * so free both.
 442          */
 443         release_task_stack(tsk);
 444 #else
 445         /*
 446          * If the task had a separate stack allocation, it should be gone
 447          * by now.
 448          */
 449         WARN_ON_ONCE(refcount_read(&tsk->stack_refcount) != 0);
 450 #endif
 451         rt_mutex_debug_task_free(tsk);
 452         ftrace_graph_exit_task(tsk);
 453         put_seccomp_filter(tsk);
 454         arch_release_task_struct(tsk);
 455         if (tsk->flags & PF_KTHREAD)
 456                 free_kthread_struct(tsk);
 457         free_task_struct(tsk);
 458 }
 459 EXPORT_SYMBOL(free_task);
 460
 461 #ifdef CONFIG_MMU
 462 static __latent_entropy int dup_mmap(struct mm_struct *mm,
 463                                         struct mm_struct *oldmm)
 464 {
 465         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 466         struct rb_node **rb_link, *rb_parent;
 467         int retval;
 468         unsigned long charge;
 469         LIST_HEAD(uf);
 470
 471         uprobe_start_dup_mmap();
 472         if (down_write_killable(&oldmm->mmap_sem)) {
 473                 retval = -EINTR;
 474                 goto fail_uprobe_end;
 475         }
 476         flush_cache_dup_mm(oldmm);
 477         uprobe_dup_mmap(oldmm, mm);
 478         /*
 479          * Not linked in yet - no deadlock potential:
 480          */
 481         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 482
 483         /* No ordering required: file already has been exposed. */
 484         RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
 485
 486         mm->total_vm = oldmm->total_vm;
 487         mm->data_vm = oldmm->data_vm;
 488         mm->exec_vm = oldmm->exec_vm;
 489         mm->stack_vm = oldmm->stack_vm;
 490
 491         rb_link = &mm->mm_rb.rb_node;
 492         rb_parent = NULL;
 493         pprev = &mm->mmap;
 494         retval = ksm_fork(mm, oldmm);
 495         if (retval)
 496                 goto out;
 497         retval = khugepaged_fork(mm, oldmm);
 498         if (retval)
 499                 goto out;
 500
 501         prev = NULL;
 502         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 503                 struct file *file;
 504
 505                 if (mpnt->vm_flags & VM_DONTCOPY) {
 506                         vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt));
 507                         continue;
 508                 }
 509                 charge = 0;
 510                 /*
 511                  * Don't duplicate many vmas if we've been oom-killed (for
 512                  * example)
 513                  */
 514                 if (fatal_signal_pending(current)) {
 515                         retval = -EINTR;
 516                         goto out;
 517                 }
 518                 if (mpnt->vm_flags & VM_ACCOUNT) {
 519                         unsigned long len = vma_pages(mpnt);
 520
 521                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
 522                                 goto fail_nomem;
 523                         charge = len;
 524                 }
 525                 tmp = vm_area_dup(mpnt);
 526                 if (!tmp)
 527                         goto fail_nomem;
 528                 retval = vma_dup_policy(mpnt, tmp);
 529                 if (retval)
 530                         goto fail_nomem_policy;
 531                 tmp->vm_mm = mm;
 532                 retval = dup_userfaultfd(tmp, &uf);
 533                 if (retval)
 534                         goto fail_nomem_anon_vma_fork;
 535                 if (tmp->vm_flags & VM_WIPEONFORK) {
 536                         /* VM_WIPEONFORK gets a clean slate in the child. */
 537                         tmp->anon_vma = NULL;
 538                         if (anon_vma_prepare(tmp))
 539                                 goto fail_nomem_anon_vma_fork;
 540                 } else if (anon_vma_fork(tmp, mpnt))
 541                         goto fail_nomem_anon_vma_fork;
 542                 tmp->vm_flags &= ~(VM_LOCKED | VM_LOCKONFAULT);
 543                 tmp->vm_next = tmp->vm_prev = NULL;
 544                 file = tmp->vm_file;
 545                 if (file) {
 546                         struct inode *inode = file_inode(file);
 547                         struct address_space *mapping = file->f_mapping;
 548
 549                         get_file(file);
 550                         if (tmp->vm_flags & VM_DENYWRITE)
 551                                 atomic_dec(&inode->i_writecount);
 552                         i_mmap_lock_write(mapping);
 553                         if (tmp->vm_flags & VM_SHARED)
 554                                 atomic_inc(&mapping->i_mmap_writable);
 555                         flush_dcache_mmap_lock(mapping);
 556                         /* insert tmp into the share list, just after mpnt */
 557                         vma_interval_tree_insert_after(tmp, mpnt,
 558                                         &mapping->i_mmap);
 559                         flush_dcache_mmap_unlock(mapping);
 560                         i_mmap_unlock_write(mapping);
 561                 }
 562
 563                 /*
 564                  * Clear hugetlb-related page reserves for children. This only
 565                  * affects MAP_PRIVATE mappings. Faults generated by the child
 566                  * are not guaranteed to succeed, even if read-only
 567                  */
 568                 if (is_vm_hugetlb_page(tmp))
 569                         reset_vma_resv_huge_pages(tmp);
 570
 571                 /*
 572                  * Link in the new vma and copy the page table entries.
 573                  */
 574                 *pprev = tmp;
 575                 pprev = &tmp->vm_next;
 576                 tmp->vm_prev = prev;
 577                 prev = tmp;
 578
 579                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 580                 rb_link = &tmp->vm_rb.rb_right;
 581                 rb_parent = &tmp->vm_rb;
 582
 583                 mm->map_count++;
 584                 if (!(tmp->vm_flags & VM_WIPEONFORK))
 585                         retval = copy_page_range(mm, oldmm, mpnt);
 586
 587                 if (tmp->vm_ops && tmp->vm_ops->open)
 588                         tmp->vm_ops->open(tmp);
 589
 590                 if (retval)
 591                         goto out;
 592         }
 593         /* a new mm has just been created */
 594         retval = arch_dup_mmap(oldmm, mm);
 595 out:
 596         up_write(&mm->mmap_sem);
 597         flush_tlb_mm(oldmm);
 598         up_write(&oldmm->mmap_sem);
 599         dup_userfaultfd_complete(&uf);
 600 fail_uprobe_end:
 601         uprobe_end_dup_mmap();
 602         return retval;
 603 fail_nomem_anon_vma_fork:
 604         mpol_put(vma_policy(tmp));
 605 fail_nomem_policy:
 606         vm_area_free(tmp);
 607 fail_nomem:
 608         retval = -ENOMEM;
 609         vm_unacct_memory(charge);
 610         goto out;
 611 }
 612
 613 static inline int mm_alloc_pgd(struct mm_struct *mm)
 614 {
 615         mm->pgd = pgd_alloc(mm);
 616         if (unlikely(!mm->pgd))
 617                 return -ENOMEM;
 618         return 0;
 619 }
 620
 621 static inline void mm_free_pgd(struct mm_struct *mm)
 622 {
 623         pgd_free(mm, mm->pgd);
 624 }
 625 #else
 626 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 627 {
 628         down_write(&oldmm->mmap_sem);
 629         RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
 630         up_write(&oldmm->mmap_sem);
 631         return 0;
 632 }
 633 #define mm_alloc_pgd(mm)        (0)
 634 #define mm_free_pgd(mm)
 635 #endif /* CONFIG_MMU */
 636
 637 static void check_mm(struct mm_struct *mm)
 638 {
 639         int i;
 640
 641         for (i = 0; i < NR_MM_COUNTERS; i++) {
 642                 long x = atomic_long_read(&mm->rss_stat.count[i]);
 643
 644                 if (unlikely(x))
 645                         printk(KERN_ALERT "BUG: Bad rss-counter state "
 646                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
 647         }
 648
 649         if (mm_pgtables_bytes(mm))
 650                 pr_alert("BUG: non-zero pgtables_bytes on freeing mm: %ld\n",
 651                                 mm_pgtables_bytes(mm));
 652
 653 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 654         VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
 655 #endif
 656 }
 657
 658 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 659 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 660
 661 /*
 662  * Called when the last reference to the mm
 663  * is dropped: either by a lazy thread or by
 664  * mmput. Free the page directory and the mm.
 665  */
 666 void __mmdrop(struct mm_struct *mm)
 667 {
 668         BUG_ON(mm == &init_mm);
 669         WARN_ON_ONCE(mm == current->mm);
 670         WARN_ON_ONCE(mm == current->active_mm);
 671         mm_free_pgd(mm);
 672         destroy_context(mm);
 673         hmm_mm_destroy(mm);
 674         mmu_notifier_mm_destroy(mm);
 675         check_mm(mm);
 676         put_user_ns(mm->user_ns);
 677         free_mm(mm);
 678 }
 679 EXPORT_SYMBOL_GPL(__mmdrop);
 680
 681 static void mmdrop_async_fn(struct work_struct *work)
 682 {
 683         struct mm_struct *mm;
 684
 685         mm = container_of(work, struct mm_struct, async_put_work);
 686         __mmdrop(mm);
 687 }
 688
 689 static void mmdrop_async(struct mm_struct *mm)
 690 {
 691         if (unlikely(atomic_dec_and_test(&mm->mm_count))) {
 692                 INIT_WORK(&mm->async_put_work, mmdrop_async_fn);
 693                 schedule_work(&mm->async_put_work);
 694         }
 695 }
 696
 697 static inline void free_signal_struct(struct signal_struct *sig)
 698 {
 699         taskstats_tgid_free(sig);
 700         sched_autogroup_exit(sig);
 701         /*
 702          * __mmdrop is not safe to call from softirq context on x86 due to
 703          * pgd_dtor so postpone it to the async context
 704          */
 705         if (sig->oom_mm)
 706                 mmdrop_async(sig->oom_mm);
 707         kmem_cache_free(signal_cachep, sig);
 708 }
 709
 710 static inline void put_signal_struct(struct signal_struct *sig)
 711 {
 712         if (refcount_dec_and_test(&sig->sigcnt))
 713                 free_signal_struct(sig);
 714 }
 715
 716 void __put_task_struct(struct task_struct *tsk)
 717 {
 718         WARN_ON(!tsk->exit_state);
 719         WARN_ON(refcount_read(&tsk->usage));
 720         WARN_ON(tsk == current);
 721
 722         cgroup_free(tsk);
 723         task_numa_free(tsk);
 724         security_task_free(tsk);
 725         exit_creds(tsk);
 726         delayacct_tsk_free(tsk);
 727         put_signal_struct(tsk->signal);
 728
 729         if (!profile_handoff_task(tsk))
 730                 free_task(tsk);
 731 }
 732 EXPORT_SYMBOL_GPL(__put_task_struct);
 733
 734 void __init __weak arch_task_cache_init(void) { }
 735
 736 /*
 737  * set_max_threads
 738  */
 739 static void set_max_threads(unsigned int max_threads_suggested)
 740 {
 741         u64 threads;
 742         unsigned long nr_pages = totalram_pages();
 743
 744         /*
 745          * The number of threads shall be limited such that the thread
 746          * structures may only consume a small part of the available memory.
 747          */
 748         if (fls64(nr_pages) + fls64(PAGE_SIZE) > 64)
 749                 threads = MAX_THREADS;
 750         else
 751                 threads = div64_u64((u64) nr_pages * (u64) PAGE_SIZE,
 752                                     (u64) THREAD_SIZE * 8UL);
 753
 754         if (threads > max_threads_suggested)
 755                 threads = max_threads_suggested;
 756
 757         max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
 758 }
 759
 760 #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
 761 /* Initialized by the architecture: */
 762 int arch_task_struct_size __read_mostly;
 763 #endif
 764
 765 static void task_struct_whitelist(unsigned long *offset, unsigned long *size)
 766 {
 767         /* Fetch thread_struct whitelist for the architecture. */
 768         arch_thread_struct_whitelist(offset, size);
 769
 770         /*
 771          * Handle zero-sized whitelist or empty thread_struct, otherwise
 772          * adjust offset to position of thread_struct in task_struct.
 773          */
 774         if (unlikely(*size == 0))
 775                 *offset = 0;
 776         else
 777                 *offset += offsetof(struct task_struct, thread);
 778 }
 779
 780 void __init fork_init(void)
 781 {
 782         int i;
 783 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 784 #ifndef ARCH_MIN_TASKALIGN
 785 #define ARCH_MIN_TASKALIGN      0
 786 #endif
 787         int align = max_t(int, L1_CACHE_BYTES, ARCH_MIN_TASKALIGN);
 788         unsigned long useroffset, usersize;
 789
 790         /* create a slab on which task_structs can be allocated */
 791         task_struct_whitelist(&useroffset, &usersize);
 792         task_struct_cachep = kmem_cache_create_usercopy("task_struct",
 793                         arch_task_struct_size, align,
 794                         SLAB_PANIC|SLAB_ACCOUNT,
 795                         useroffset, usersize, NULL);
 796 #endif
 797
 798         /* do the arch specific task caches init */
 799         arch_task_cache_init();
 800
 801         set_max_threads(MAX_THREADS);
 802
 803         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 804         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
 805         init_task.signal->rlim[RLIMIT_SIGPENDING] =
 806                 init_task.signal->rlim[RLIMIT_NPROC];
 807
 808         for (i = 0; i < UCOUNT_COUNTS; i++) {
 809                 init_user_ns.ucount_max[i] = max_threads/2;
 810         }
 811
 812 #ifdef CONFIG_VMAP_STACK
 813         cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
 814                           NULL, free_vm_stack_cache);
 815 #endif
 816
 817         lockdep_init_task(&init_task);
 818         uprobes_init();
 819 }
 820
 821 int __weak arch_dup_task_struct(struct task_struct *dst,
 822                                                struct task_struct *src)
 823 {
 824         *dst = *src;
 825         return 0;
 826 }
 827
 828 void set_task_stack_end_magic(struct task_struct *tsk)
 829 {
 830         unsigned long *stackend;
 831
 832         stackend = end_of_stack(tsk);
 833         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 834 }
 835
 836 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 837 {
 838         struct task_struct *tsk;
 839         unsigned long *stack;
 840         struct vm_struct *stack_vm_area __maybe_unused;
 841         int err;
 842
 843         if (node == NUMA_NO_NODE)
 844                 node = tsk_fork_get_node(orig);
 845         tsk = alloc_task_struct_node(node);
 846         if (!tsk)
 847                 return NULL;
 848
 849         stack = alloc_thread_stack_node(tsk, node);
 850         if (!stack)
 851                 goto free_tsk;
 852
 853         if (memcg_charge_kernel_stack(tsk))
 854                 goto free_stack;
 855
 856         stack_vm_area = task_stack_vm_area(tsk);
 857
 858         err = arch_dup_task_struct(tsk, orig);
 859
 860         /*
 861          * arch_dup_task_struct() clobbers the stack-related fields.  Make
 862          * sure they're properly initialized before using any stack-related
 863          * functions again.
 864          */
 865         tsk->stack = stack;
 866 #ifdef CONFIG_VMAP_STACK
 867         tsk->stack_vm_area = stack_vm_area;
 868 #endif
 869 #ifdef CONFIG_THREAD_INFO_IN_TASK
 870         refcount_set(&tsk->stack_refcount, 1);
 871 #endif
 872
 873         if (err)
 874                 goto free_stack;
 875
 876 #ifdef CONFIG_SECCOMP
 877         /*
 878          * We must handle setting up seccomp filters once we're under
 879          * the sighand lock in case orig has changed between now and
 880          * then. Until then, filter must be NULL to avoid messing up
 881          * the usage counts on the error path calling free_task.
 882          */
 883         tsk->seccomp.filter = NULL;
 884 #endif
 885
 886         setup_thread_stack(tsk, orig);
 887         clear_user_return_notifier(tsk);
 888         clear_tsk_need_resched(tsk);
 889         set_task_stack_end_magic(tsk);
 890
 891 #ifdef CONFIG_STACKPROTECTOR
 892         tsk->stack_canary = get_random_canary();
 893 #endif
 894
 895         /*
 896          * One for us, one for whoever does the "release_task()" (usually
 897          * parent)
 898          */
 899         refcount_set(&tsk->usage, 2);
 900 #ifdef CONFIG_BLK_DEV_IO_TRACE
 901         tsk->btrace_seq = 0;
 902 #endif
 903         tsk->splice_pipe = NULL;
 904         tsk->task_frag.page = NULL;
 905         tsk->wake_q.next = NULL;
 906
 907         account_kernel_stack(tsk, 1);
 908
 909         kcov_task_init(tsk);
 910
 911 #ifdef CONFIG_FAULT_INJECTION
 912         tsk->fail_nth = 0;
 913 #endif
 914
 915 #ifdef CONFIG_BLK_CGROUP
 916         tsk->throttle_queue = NULL;
 917         tsk->use_memdelay = 0;
 918 #endif
 919
 920 #ifdef CONFIG_MEMCG
 921         tsk->active_memcg = NULL;
 922 #endif
 923         return tsk;
 924
 925 free_stack:
 926         free_thread_stack(tsk);
 927 free_tsk:
 928         free_task_struct(tsk);
 929         return NULL;
 930 }
 931
 932 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 933
 934 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 935
 936 static int __init coredump_filter_setup(char *s)
 937 {
 938         default_dump_filter =
 939                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 940                 MMF_DUMP_FILTER_MASK;
 941         return 1;
 942 }
 943
 944 __setup("coredump_filter=", coredump_filter_setup);
 945
 946 #include <linux/init_task.h>
 947
 948 static void mm_init_aio(struct mm_struct *mm)
 949 {
 950 #ifdef CONFIG_AIO
 951         spin_lock_init(&mm->ioctx_lock);
 952         mm->ioctx_table = NULL;
 953 #endif
 954 }
 955
 956 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
 957 {
 958 #ifdef CONFIG_MEMCG
 959         mm->owner = p;
 960 #endif
 961 }
 962
 963 static void mm_init_uprobes_state(struct mm_struct *mm)
 964 {
 965 #ifdef CONFIG_UPROBES
 966         mm->uprobes_state.xol_area = NULL;
 967 #endif
 968 }
 969
 970 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 971         struct user_namespace *user_ns)
 972 {
 973         mm->mmap = NULL;
 974         mm->mm_rb = RB_ROOT;
 975         mm->vmacache_seqnum = 0;
 976         atomic_set(&mm->mm_users, 1);
 977         atomic_set(&mm->mm_count, 1);
 978         init_rwsem(&mm->mmap_sem);
 979         INIT_LIST_HEAD(&mm->mmlist);
 980         mm->core_state = NULL;
 981         mm_pgtables_bytes_init(mm);
 982         mm->map_count = 0;
 983         mm->locked_vm = 0;
 984         atomic64_set(&mm->pinned_vm, 0);
 985         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 986         spin_lock_init(&mm->page_table_lock);
 987         spin_lock_init(&mm->arg_lock);
 988         mm_init_cpumask(mm);
 989         mm_init_aio(mm);
 990         mm_init_owner(mm, p);
 991         RCU_INIT_POINTER(mm->exe_file, NULL);
 992         mmu_notifier_mm_init(mm);
 993         hmm_mm_init(mm);
 994         init_tlb_flush_pending(mm);
 995 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 996         mm->pmd_huge_pte = NULL;
 997 #endif
 998         mm_init_uprobes_state(mm);
 999
1000         if (current->mm) {
1001                 mm->flags = current->mm->flags & MMF_INIT_MASK;
1002                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
1003         } else {
1004                 mm->flags = default_dump_filter;
1005                 mm->def_flags = 0;
1006         }
1007
1008         if (mm_alloc_pgd(mm))
1009                 goto fail_nopgd;
1010
1011         if (init_new_context(p, mm))
1012                 goto fail_nocontext;
1013
1014         mm->user_ns = get_user_ns(user_ns);
1015         return mm;
1016
1017 fail_nocontext:
1018         mm_free_pgd(mm);
1019 fail_nopgd:
1020         free_mm(mm);
1021         return NULL;
1022 }
1023
1024 /*
1025  * Allocate and initialize an mm_struct.
1026  */
1027 struct mm_struct *mm_alloc(void)
1028 {
1029         struct mm_struct *mm;
1030
1031         mm = allocate_mm();
1032         if (!mm)
1033                 return NULL;
1034
1035         memset(mm, 0, sizeof(*mm));
1036         return mm_init(mm, current, current_user_ns());
1037 }
1038
1039 static inline void __mmput(struct mm_struct *mm)
1040 {
1041         VM_BUG_ON(atomic_read(&mm->mm_users));
1042
1043         uprobe_clear_state(mm);
1044         exit_aio(mm);
1045         ksm_exit(mm);
1046         khugepaged_exit(mm); /* must run before exit_mmap */
1047         exit_mmap(mm);
1048         mm_put_huge_zero_page(mm);
1049         set_mm_exe_file(mm, NULL);
1050         if (!list_empty(&mm->mmlist)) {
1051                 spin_lock(&mmlist_lock);
1052                 list_del(&mm->mmlist);
1053                 spin_unlock(&mmlist_lock);
1054         }
1055         if (mm->binfmt)
1056                 module_put(mm->binfmt->module);
1057         mmdrop(mm);
1058 }
1059
1060 /*
1061  * Decrement the use count and release all resources for an mm.
1062  */
1063 void mmput(struct mm_struct *mm)
1064 {
1065         might_sleep();
1066
1067         if (atomic_dec_and_test(&mm->mm_users))
1068                 __mmput(mm);
1069 }
1070 EXPORT_SYMBOL_GPL(mmput);
1071
1072 #ifdef CONFIG_MMU
1073 static void mmput_async_fn(struct work_struct *work)
1074 {
1075         struct mm_struct *mm = container_of(work, struct mm_struct,
1076                                             async_put_work);
1077
1078         __mmput(mm);
1079 }
1080
1081 void mmput_async(struct mm_struct *mm)
1082 {
1083         if (atomic_dec_and_test(&mm->mm_users)) {
1084                 INIT_WORK(&mm->async_put_work, mmput_async_fn);
1085                 schedule_work(&mm->async_put_work);
1086         }
1087 }
1088 #endif
1089
1090 /**
1091  * set_mm_exe_file - change a reference to the mm's executable file
1092  *
1093  * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
1094  *
1095  * Main users are mmput() and sys_execve(). Callers prevent concurrent
1096  * invocations: in mmput() nobody alive left, in execve task is single
1097  * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
1098  * mm->exe_file, but does so without using set_mm_exe_file() in order
1099  * to do avoid the need for any locks.
1100  */
1101 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
1102 {
1103         struct file *old_exe_file;
1104
1105         /*
1106          * It is safe to dereference the exe_file without RCU as
1107          * this function is only called if nobody else can access
1108          * this mm -- see comment above for justification.
1109          */
1110         old_exe_file = rcu_dereference_raw(mm->exe_file);
1111
1112         if (new_exe_file)
1113                 get_file(new_exe_file);
1114         rcu_assign_pointer(mm->exe_file, new_exe_file);
1115         if (old_exe_file)
1116                 fput(old_exe_file);
1117 }
1118
1119 /**
1120  * get_mm_exe_file - acquire a reference to the mm's executable file
1121  *
1122  * Returns %NULL if mm has no associated executable file.
1123  * User must release file via fput().
1124  */
1125 struct file *get_mm_exe_file(struct mm_struct *mm)
1126 {
1127         struct file *exe_file;
1128
1129         rcu_read_lock();
1130         exe_file = rcu_dereference(mm->exe_file);
1131         if (exe_file && !get_file_rcu(exe_file))
1132                 exe_file = NULL;
1133         rcu_read_unlock();
1134         return exe_file;
1135 }
1136 EXPORT_SYMBOL(get_mm_exe_file);
1137
1138 /**
1139  * get_task_exe_file - acquire a reference to the task's executable file
1140  *
1141  * Returns %NULL if task's mm (if any) has no associated executable file or
1142  * this is a kernel thread with borrowed mm (see the comment above get_task_mm).
1143  * User must release file via fput().
1144  */
1145 struct file *get_task_exe_file(struct task_struct *task)
1146 {
1147         struct file *exe_file = NULL;
1148         struct mm_struct *mm;
1149
1150         task_lock(task);
1151         mm = task->mm;
1152         if (mm) {
1153                 if (!(task->flags & PF_KTHREAD))
1154                         exe_file = get_mm_exe_file(mm);
1155         }
1156         task_unlock(task);
1157         return exe_file;
1158 }
1159 EXPORT_SYMBOL(get_task_exe_file);
1160
1161 /**
1162  * get_task_mm - acquire a reference to the task's mm
1163  *
1164  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
1165  * this kernel workthread has transiently adopted a user mm with use_mm,
1166  * to do its AIO) is not set and if so returns a reference to it, after
1167  * bumping up the use count.  User must release the mm via mmput()
1168  * after use.  Typically used by /proc and ptrace.
1169  */
1170 struct mm_struct *get_task_mm(struct task_struct *task)
1171 {
1172         struct mm_struct *mm;
1173
1174         task_lock(task);
1175         mm = task->mm;
1176         if (mm) {
1177                 if (task->flags & PF_KTHREAD)
1178                         mm = NULL;
1179                 else
1180                         mmget(mm);
1181         }
1182         task_unlock(task);
1183         return mm;
1184 }
1185 EXPORT_SYMBOL_GPL(get_task_mm);
1186
1187 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
1188 {
1189         struct mm_struct *mm;
1190         int err;
1191
1192         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
1193         if (err)
1194                 return ERR_PTR(err);
1195
1196         mm = get_task_mm(task);
1197         if (mm && mm != current->mm &&
1198                         !ptrace_may_access(task, mode)) {
1199                 mmput(mm);
1200                 mm = ERR_PTR(-EACCES);
1201         }
1202         mutex_unlock(&task->signal->cred_guard_mutex);
1203
1204         return mm;
1205 }
1206
1207 static void complete_vfork_done(struct task_struct *tsk)
1208 {
1209         struct completion *vfork;
1210
1211         task_lock(tsk);
1212         vfork = tsk->vfork_done;
1213         if (likely(vfork)) {
1214                 tsk->vfork_done = NULL;
1215                 complete(vfork);
1216         }
1217         task_unlock(tsk);
1218 }
1219
1220 static int wait_for_vfork_done(struct task_struct *child,
1221                                 struct completion *vfork)
1222 {
1223         int killed;
1224
1225         freezer_do_not_count();
1226         killed = wait_for_completion_killable(vfork);
1227         freezer_count();
1228
1229         if (killed) {
1230                 task_lock(child);
1231                 child->vfork_done = NULL;
1232                 task_unlock(child);
1233         }
1234
1235         put_task_struct(child);
1236         return killed;
1237 }
1238
1239 /* Please note the differences between mmput and mm_release.
1240  * mmput is called whenever we stop holding onto a mm_struct,
1241  * error success whatever.
1242  *
1243  * mm_release is called after a mm_struct has been removed
1244  * from the current process.
1245  *
1246  * This difference is important for error handling, when we
1247  * only half set up a mm_struct for a new process and need to restore
1248  * the old one.  Because we mmput the new mm_struct before
1249  * restoring the old one. . .
1250  * Eric Biederman 10 January 1998
1251  */
1252 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
1253 {
1254         /* Get rid of any futexes when releasing the mm */
1255 #ifdef CONFIG_FUTEX
1256         if (unlikely(tsk->robust_list)) {
1257                 exit_robust_list(tsk);
1258                 tsk->robust_list = NULL;
1259         }
1260 #ifdef CONFIG_COMPAT
1261         if (unlikely(tsk->compat_robust_list)) {
1262                 compat_exit_robust_list(tsk);
1263                 tsk->compat_robust_list = NULL;
1264         }
1265 #endif
1266         if (unlikely(!list_empty(&tsk->pi_state_list)))
1267                 exit_pi_state_list(tsk);
1268 #endif
1269
1270         uprobe_free_utask(tsk);
1271
1272         /* Get rid of any cached register state */
1273         deactivate_mm(tsk, mm);
1274
1275         /*
1276          * Signal userspace if we're not exiting with a core dump
1277          * because we want to leave the value intact for debugging
1278          * purposes.
1279          */
1280         if (tsk->clear_child_tid) {
1281                 if (!(tsk->signal->flags & SIGNAL_GROUP_COREDUMP) &&
1282                     atomic_read(&mm->mm_users) > 1) {
1283                         /*
1284                          * We don't check the error code - if userspace has
1285                          * not set up a proper pointer then tough luck.
1286                          */
1287                         put_user(0, tsk->clear_child_tid);
1288                         do_futex(tsk->clear_child_tid, FUTEX_WAKE,
1289                                         1, NULL, NULL, 0, 0);
1290                 }
1291                 tsk->clear_child_tid = NULL;
1292         }
1293
1294         /*
1295          * All done, finally we can wake up parent and return this mm to him.
1296          * Also kthread_stop() uses this completion for synchronization.
1297          */
1298         if (tsk->vfork_done)
1299                 complete_vfork_done(tsk);
1300 }
1301
1302 /**
1303  * dup_mm() - duplicates an existing mm structure
1304  * @tsk: the task_struct with which the new mm will be associated.
1305  * @oldmm: the mm to duplicate.
1306  *
1307  * Allocates a new mm structure and duplicates the provided @oldmm structure
1308  * content into it.
1309  *
1310  * Return: the duplicated mm or NULL on failure.
1311  */
1312 static struct mm_struct *dup_mm(struct task_struct *tsk,
1313                                 struct mm_struct *oldmm)
1314 {
1315         struct mm_struct *mm;
1316         int err;
1317
1318         mm = allocate_mm();
1319         if (!mm)
1320                 goto fail_nomem;
1321
1322         memcpy(mm, oldmm, sizeof(*mm));
1323
1324         if (!mm_init(mm, tsk, mm->user_ns))
1325                 goto fail_nomem;
1326
1327         err = dup_mmap(mm, oldmm);
1328         if (err)
1329                 goto free_pt;
1330
1331         mm->hiwater_rss = get_mm_rss(mm);
1332         mm->hiwater_vm = mm->total_vm;
1333
1334         if (mm->binfmt && !try_module_get(mm->binfmt->module))
1335                 goto free_pt;
1336
1337         return mm;
1338
1339 free_pt:
1340         /* don't put binfmt in mmput, we haven't got module yet */
1341         mm->binfmt = NULL;
1342         mmput(mm);
1343
1344 fail_nomem:
1345         return NULL;
1346 }
1347
1348 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
1349 {
1350         struct mm_struct *mm, *oldmm;
1351         int retval;
1352
1353         tsk->min_flt = tsk->maj_flt = 0;
1354         tsk->nvcsw = tsk->nivcsw = 0;
1355 #ifdef CONFIG_DETECT_HUNG_TASK
1356         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
1357         tsk->last_switch_time = 0;
1358 #endif
1359
1360         tsk->mm = NULL;
1361         tsk->active_mm = NULL;
1362
1363         /*
1364          * Are we cloning a kernel thread?
1365          *
1366          * We need to steal a active VM for that..
1367          */
1368         oldmm = current->mm;
1369         if (!oldmm)
1370                 return 0;
1371
1372         /* initialize the new vmacache entries */
1373         vmacache_flush(tsk);
1374
1375         if (clone_flags & CLONE_VM) {
1376                 mmget(oldmm);
1377                 mm = oldmm;
1378                 goto good_mm;
1379         }
1380
1381         retval = -ENOMEM;
1382         mm = dup_mm(tsk, current->mm);
1383         if (!mm)
1384                 goto fail_nomem;
1385
1386 good_mm:
1387         tsk->mm = mm;
1388         tsk->active_mm = mm;
1389         return 0;
1390
1391 fail_nomem:
1392         return retval;
1393 }
1394
1395 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
1396 {
1397         struct fs_struct *fs = current->fs;
1398         if (clone_flags & CLONE_FS) {
1399                 /* tsk->fs is already what we want */
1400                 spin_lock(&fs->lock);
1401                 if (fs->in_exec) {
1402                         spin_unlock(&fs->lock);
1403                         return -EAGAIN;
1404                 }
1405                 fs->users++;
1406                 spin_unlock(&fs->lock);
1407                 return 0;
1408         }
1409         tsk->fs = copy_fs_struct(fs);
1410         if (!tsk->fs)
1411                 return -ENOMEM;
1412         return 0;
1413 }
1414
1415 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
1416 {
1417         struct files_struct *oldf, *newf;
1418         int error = 0;
1419
1420         /*
1421          * A background process may not have any files ...
1422          */
1423         oldf = current->files;
1424         if (!oldf)
1425                 goto out;
1426
1427         if (clone_flags & CLONE_FILES) {
1428                 atomic_inc(&oldf->count);
1429                 goto out;
1430         }
1431
1432         newf = dup_fd(oldf, &error);
1433         if (!newf)
1434                 goto out;
1435
1436         tsk->files = newf;
1437         error = 0;
1438 out:
1439         return error;
1440 }
1441
1442 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
1443 {
1444 #ifdef CONFIG_BLOCK
1445         struct io_context *ioc = current->io_context;
1446         struct io_context *new_ioc;
1447
1448         if (!ioc)
1449                 return 0;
1450         /*
1451          * Share io context with parent, if CLONE_IO is set
1452          */
1453         if (clone_flags & CLONE_IO) {
1454                 ioc_task_link(ioc);
1455                 tsk->io_context = ioc;
1456         } else if (ioprio_valid(ioc->ioprio)) {
1457                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
1458                 if (unlikely(!new_ioc))
1459                         return -ENOMEM;
1460
1461                 new_ioc->ioprio = ioc->ioprio;
1462                 put_io_context(new_ioc);
1463         }
1464 #endif
1465         return 0;
1466 }
1467
1468 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1469 {
1470         struct sighand_struct *sig;
1471
1472         if (clone_flags & CLONE_SIGHAND) {
1473                 refcount_inc(&current->sighand->count);
1474                 return 0;
1475         }
1476         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1477         rcu_assign_pointer(tsk->sighand, sig);
1478         if (!sig)
1479                 return -ENOMEM;
1480
1481         refcount_set(&sig->count, 1);
1482         spin_lock_irq(&current->sighand->siglock);
1483         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1484         spin_unlock_irq(&current->sighand->siglock);
1485         return 0;
1486 }
1487
1488 void __cleanup_sighand(struct sighand_struct *sighand)
1489 {
1490         if (refcount_dec_and_test(&sighand->count)) {
1491                 signalfd_cleanup(sighand);
1492                 /*
1493                  * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it
1494                  * without an RCU grace period, see __lock_task_sighand().
1495                  */
1496                 kmem_cache_free(sighand_cachep, sighand);
1497         }
1498 }
1499
1500 #ifdef CONFIG_POSIX_TIMERS
1501 /*
1502  * Initialize POSIX timer handling for a thread group.
1503  */
1504 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1505 {
1506         unsigned long cpu_limit;
1507
1508         cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1509         if (cpu_limit != RLIM_INFINITY) {
1510                 sig->cputime_expires.prof_exp = cpu_limit * NSEC_PER_SEC;
1511                 sig->cputimer.running = true;
1512         }
1513
1514         /* The timer lists. */
1515         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1516         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1517         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1518 }
1519 #else
1520 static inline void posix_cpu_timers_init_group(struct signal_struct *sig) { }
1521 #endif
1522
1523 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1524 {
1525         struct signal_struct *sig;
1526
1527         if (clone_flags & CLONE_THREAD)
1528                 return 0;
1529
1530         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1531         tsk->signal = sig;
1532         if (!sig)
1533                 return -ENOMEM;
1534
1535         sig->nr_threads = 1;
1536         atomic_set(&sig->live, 1);
1537         refcount_set(&sig->sigcnt, 1);
1538
1539         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1540         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1541         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1542
1543         init_waitqueue_head(&sig->wait_chldexit);
1544         sig->curr_target = tsk;
1545         init_sigpending(&sig->shared_pending);
1546         INIT_HLIST_HEAD(&sig->multiprocess);
1547         seqlock_init(&sig->stats_lock);
1548         prev_cputime_init(&sig->prev_cputime);
1549
1550 #ifdef CONFIG_POSIX_TIMERS
1551         INIT_LIST_HEAD(&sig->posix_timers);
1552         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1553         sig->real_timer.function = it_real_fn;
1554 #endif
1555
1556         task_lock(current->group_leader);
1557         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1558         task_unlock(current->group_leader);
1559
1560         posix_cpu_timers_init_group(sig);
1561
1562         tty_audit_fork(sig);
1563         sched_autogroup_fork(sig);
1564
1565         sig->oom_score_adj = current->signal->oom_score_adj;
1566         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1567
1568         mutex_init(&sig->cred_guard_mutex);
1569
1570         return 0;
1571 }
1572
1573 static void copy_seccomp(struct task_struct *p)
1574 {
1575 #ifdef CONFIG_SECCOMP
1576         /*
1577          * Must be called with sighand->lock held, which is common to
1578          * all threads in the group. Holding cred_guard_mutex is not
1579          * needed because this new task is not yet running and cannot
1580          * be racing exec.
1581          */
1582         assert_spin_locked(&current->sighand->siglock);
1583
1584         /* Ref-count the new filter user, and assign it. */
1585         get_seccomp_filter(current);
1586         p->seccomp = current->seccomp;
1587
1588         /*
1589          * Explicitly enable no_new_privs here in case it got set
1590          * between the task_struct being duplicated and holding the
1591          * sighand lock. The seccomp state and nnp must be in sync.
1592          */
1593         if (task_no_new_privs(current))
1594                 task_set_no_new_privs(p);
1595
1596         /*
1597          * If the parent gained a seccomp mode after copying thread
1598          * flags and between before we held the sighand lock, we have
1599          * to manually enable the seccomp thread flag here.
1600          */
1601         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1602                 set_tsk_thread_flag(p, TIF_SECCOMP);
1603 #endif
1604 }
1605
1606 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1607 {
1608         current->clear_child_tid = tidptr;
1609
1610         return task_pid_vnr(current);
1611 }
1612
1613 static void rt_mutex_init_task(struct task_struct *p)
1614 {
1615         raw_spin_lock_init(&p->pi_lock);
1616 #ifdef CONFIG_RT_MUTEXES
1617         p->pi_waiters = RB_ROOT_CACHED;
1618         p->pi_top_task = NULL;
1619         p->pi_blocked_on = NULL;
1620 #endif
1621 }
1622
1623 #ifdef CONFIG_POSIX_TIMERS
1624 /*
1625  * Initialize POSIX timer handling for a single task.
1626  */
1627 static void posix_cpu_timers_init(struct task_struct *tsk)
1628 {
1629         tsk->cputime_expires.prof_exp = 0;
1630         tsk->cputime_expires.virt_exp = 0;
1631         tsk->cputime_expires.sched_exp = 0;
1632         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1633         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1634         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1635 }
1636 #else
1637 static inline void posix_cpu_timers_init(struct task_struct *tsk) { }
1638 #endif
1639
1640 static inline void init_task_pid_links(struct task_struct *task)
1641 {
1642         enum pid_type type;
1643
1644         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1645                 INIT_HLIST_NODE(&task->pid_links[type]);
1646         }
1647 }
1648
1649 static inline void
1650 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1651 {
1652         if (type == PIDTYPE_PID)
1653                 task->thread_pid = pid;
1654         else
1655                 task->signal->pids[type] = pid;
1656 }
1657
1658 static inline void rcu_copy_process(struct task_struct *p)
1659 {
1660 #ifdef CONFIG_PREEMPT_RCU
1661         p->rcu_read_lock_nesting = 0;
1662         p->rcu_read_unlock_special.s = 0;
1663         p->rcu_blocked_node = NULL;
1664         INIT_LIST_HEAD(&p->rcu_node_entry);
1665 #endif /* #ifdef CONFIG_PREEMPT_RCU */
1666 #ifdef CONFIG_TASKS_RCU
1667         p->rcu_tasks_holdout = false;
1668         INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
1669         p->rcu_tasks_idle_cpu = -1;
1670 #endif /* #ifdef CONFIG_TASKS_RCU */
1671 }
1672
1673 /*
1674  * This creates a new process as a copy of the old one,
1675  * but does not actually start it yet.
1676  *
1677  * It copies the registers, and all the appropriate
1678  * parts of the process environment (as per the clone
1679  * flags). The actual kick-off is left to the caller.
1680  */
1681 static __latent_entropy struct task_struct *copy_process(
1682                                         unsigned long clone_flags,
1683                                         unsigned long stack_start,
1684                                         unsigned long stack_size,
1685                                         int __user *child_tidptr,
1686                                         struct pid *pid,
1687                                         int trace,
1688                                         unsigned long tls,
1689                                         int node)
1690 {
1691         int retval;
1692         struct task_struct *p;
1693         struct multiprocess_signals delayed;
1694
1695         /*
1696          * Don't allow sharing the root directory with processes in a different
1697          * namespace
1698          */
1699         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1700                 return ERR_PTR(-EINVAL);
1701
1702         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1703                 return ERR_PTR(-EINVAL);
1704
1705         /*
1706          * Thread groups must share signals as well, and detached threads
1707          * can only be started up within the thread group.
1708          */
1709         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1710                 return ERR_PTR(-EINVAL);
1711
1712         /*
1713          * Shared signal handlers imply shared VM. By way of the above,
1714          * thread groups also imply shared VM. Blocking this case allows
1715          * for various simplifications in other code.
1716          */
1717         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1718                 return ERR_PTR(-EINVAL);
1719
1720         /*
1721          * Siblings of global init remain as zombies on exit since they are
1722          * not reaped by their parent (swapper). To solve this and to avoid
1723          * multi-rooted process trees, prevent global and container-inits
1724          * from creating siblings.
1725          */
1726         if ((clone_flags & CLONE_PARENT) &&
1727                                 current->signal->flags & SIGNAL_UNKILLABLE)
1728                 return ERR_PTR(-EINVAL);
1729
1730         /*
1731          * If the new process will be in a different pid or user namespace
1732          * do not allow it to share a thread group with the forking task.
1733          */
1734         if (clone_flags & CLONE_THREAD) {
1735                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1736                     (task_active_pid_ns(current) !=
1737                                 current->nsproxy->pid_ns_for_children))
1738                         return ERR_PTR(-EINVAL);
1739         }
1740
1741         /*
1742          * Force any signals received before this point to be delivered
1743          * before the fork happens.  Collect up signals sent to multiple
1744          * processes that happen during the fork and delay them so that
1745          * they appear to happen after the fork.
1746          */
1747         sigemptyset(&delayed.signal);
1748         INIT_HLIST_NODE(&delayed.node);
1749
1750         spin_lock_irq(&current->sighand->siglock);
1751         if (!(clone_flags & CLONE_THREAD))
1752                 hlist_add_head(&delayed.node, &current->signal->multiprocess);
1753         recalc_sigpending();
1754         spin_unlock_irq(&current->sighand->siglock);
1755         retval = -ERESTARTNOINTR;
1756         if (signal_pending(current))
1757                 goto fork_out;
1758
1759         retval = -ENOMEM;
1760         p = dup_task_struct(current, node);
1761         if (!p)
1762                 goto fork_out;
1763
1764         /*
1765          * This _must_ happen before we call free_task(), i.e. before we jump
1766          * to any of the bad_fork_* labels. This is to avoid freeing
1767          * p->set_child_tid which is (ab)used as a kthread's data pointer for
1768          * kernel threads (PF_KTHREAD).
1769          */
1770         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1771         /*
1772          * Clear TID on mm_release()?
1773          */
1774         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1775
1776         ftrace_graph_init_task(p);
1777
1778         rt_mutex_init_task(p);
1779
1780 #ifdef CONFIG_PROVE_LOCKING
1781         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1782         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1783 #endif
1784         retval = -EAGAIN;
1785         if (atomic_read(&p->real_cred->user->processes) >=
1786                         task_rlimit(p, RLIMIT_NPROC)) {
1787                 if (p->real_cred->user != INIT_USER &&
1788                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1789                         goto bad_fork_free;
1790         }
1791         current->flags &= ~PF_NPROC_EXCEEDED;
1792
1793         retval = copy_creds(p, clone_flags);
1794         if (retval < 0)
1795                 goto bad_fork_free;
1796
1797         /*
1798          * If multiple threads are within copy_process(), then this check
1799          * triggers too late. This doesn't hurt, the check is only there
1800          * to stop root fork bombs.
1801          */
1802         retval = -EAGAIN;
1803         if (nr_threads >= max_threads)
1804                 goto bad_fork_cleanup_count;
1805
1806         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1807         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE);
1808         p->flags |= PF_FORKNOEXEC;
1809         INIT_LIST_HEAD(&p->children);
1810         INIT_LIST_HEAD(&p->sibling);
1811         rcu_copy_process(p);
1812         p->vfork_done = NULL;
1813         spin_lock_init(&p->alloc_lock);
1814
1815         init_sigpending(&p->pending);
1816
1817         p->utime = p->stime = p->gtime = 0;
1818 #ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
1819         p->utimescaled = p->stimescaled = 0;
1820 #endif
1821         prev_cputime_init(&p->prev_cputime);
1822
1823 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1824         seqcount_init(&p->vtime.seqcount);
1825         p->vtime.starttime = 0;
1826         p->vtime.state = VTIME_INACTIVE;
1827 #endif
1828
1829 #if defined(SPLIT_RSS_COUNTING)
1830         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1831 #endif
1832
1833         p->default_timer_slack_ns = current->timer_slack_ns;
1834
1835 #ifdef CONFIG_PSI
1836         p->psi_flags = 0;
1837 #endif
1838
1839         task_io_accounting_init(&p->ioac);
1840         acct_clear_integrals(p);
1841
1842         posix_cpu_timers_init(p);
1843
1844         p->io_context = NULL;
1845         audit_set_context(p, NULL);
1846         cgroup_fork(p);
1847 #ifdef CONFIG_NUMA
1848         p->mempolicy = mpol_dup(p->mempolicy);
1849         if (IS_ERR(p->mempolicy)) {
1850                 retval = PTR_ERR(p->mempolicy);
1851                 p->mempolicy = NULL;
1852                 goto bad_fork_cleanup_threadgroup_lock;
1853         }
1854 #endif
1855 #ifdef CONFIG_CPUSETS
1856         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1857         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1858         seqcount_init(&p->mems_allowed_seq);
1859 #endif
1860 #ifdef CONFIG_TRACE_IRQFLAGS
1861         p->irq_events = 0;
1862         p->hardirqs_enabled = 0;
1863         p->hardirq_enable_ip = 0;
1864         p->hardirq_enable_event = 0;
1865         p->hardirq_disable_ip = _THIS_IP_;
1866         p->hardirq_disable_event = 0;
1867         p->softirqs_enabled = 1;
1868         p->softirq_enable_ip = _THIS_IP_;
1869         p->softirq_enable_event = 0;
1870         p->softirq_disable_ip = 0;
1871         p->softirq_disable_event = 0;
1872         p->hardirq_context = 0;
1873         p->softirq_context = 0;
1874 #endif
1875
1876         p->pagefault_disabled = 0;
1877
1878 #ifdef CONFIG_LOCKDEP
1879         p->lockdep_depth = 0; /* no locks held yet */
1880         p->curr_chain_key = 0;
1881         p->lockdep_recursion = 0;
1882         lockdep_init_task(p);
1883 #endif
1884
1885 #ifdef CONFIG_DEBUG_MUTEXES
1886         p->blocked_on = NULL; /* not blocked yet */
1887 #endif
1888 #ifdef CONFIG_BCACHE
1889         p->sequential_io        = 0;
1890         p->sequential_io_avg    = 0;
1891 #endif
1892
1893         /* Perform scheduler related setup. Assign this task to a CPU. */
1894         retval = sched_fork(clone_flags, p);
1895         if (retval)
1896                 goto bad_fork_cleanup_policy;
1897
1898         retval = perf_event_init_task(p);
1899         if (retval)
1900                 goto bad_fork_cleanup_policy;
1901         retval = audit_alloc(p);
1902         if (retval)
1903                 goto bad_fork_cleanup_perf;
1904         /* copy all the process information */
1905         shm_init_task(p);
1906         retval = security_task_alloc(p, clone_flags);
1907         if (retval)
1908                 goto bad_fork_cleanup_audit;
1909         retval = copy_semundo(clone_flags, p);
1910         if (retval)
1911                 goto bad_fork_cleanup_security;
1912         retval = copy_files(clone_flags, p);
1913         if (retval)
1914                 goto bad_fork_cleanup_semundo;
1915         retval = copy_fs(clone_flags, p);
1916         if (retval)
1917                 goto bad_fork_cleanup_files;
1918         retval = copy_sighand(clone_flags, p);
1919         if (retval)
1920                 goto bad_fork_cleanup_fs;
1921         retval = copy_signal(clone_flags, p);
1922         if (retval)
1923                 goto bad_fork_cleanup_sighand;
1924         retval = copy_mm(clone_flags, p);
1925         if (retval)
1926                 goto bad_fork_cleanup_signal;
1927         retval = copy_namespaces(clone_flags, p);
1928         if (retval)
1929                 goto bad_fork_cleanup_mm;
1930         retval = copy_io(clone_flags, p);
1931         if (retval)
1932                 goto bad_fork_cleanup_namespaces;
1933         retval = copy_thread_tls(clone_flags, stack_start, stack_size, p, tls);
1934         if (retval)
1935                 goto bad_fork_cleanup_io;
1936
1937         stackleak_task_init(p);
1938
1939         if (pid != &init_struct_pid) {
1940                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1941                 if (IS_ERR(pid)) {
1942                         retval = PTR_ERR(pid);
1943                         goto bad_fork_cleanup_thread;
1944                 }
1945         }
1946
1947 #ifdef CONFIG_BLOCK
1948         p->plug = NULL;
1949 #endif
1950 #ifdef CONFIG_FUTEX
1951         p->robust_list = NULL;
1952 #ifdef CONFIG_COMPAT
1953         p->compat_robust_list = NULL;
1954 #endif
1955         INIT_LIST_HEAD(&p->pi_state_list);
1956         p->pi_state_cache = NULL;
1957 #endif
1958         /*
1959          * sigaltstack should be cleared when sharing the same VM
1960          */
1961         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1962                 sas_ss_reset(p);
1963
1964         /*
1965          * Syscall tracing and stepping should be turned off in the
1966          * child regardless of CLONE_PTRACE.
1967          */
1968         user_disable_single_step(p);
1969         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1970 #ifdef TIF_SYSCALL_EMU
1971         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1972 #endif
1973         clear_all_latency_tracing(p);
1974
1975         /* ok, now we should be set up.. */
1976         p->pid = pid_nr(pid);
1977         if (clone_flags & CLONE_THREAD) {
1978                 p->exit_signal = -1;
1979                 p->group_leader = current->group_leader;
1980                 p->tgid = current->tgid;
1981         } else {
1982                 if (clone_flags & CLONE_PARENT)
1983                         p->exit_signal = current->group_leader->exit_signal;
1984                 else
1985                         p->exit_signal = (clone_flags & CSIGNAL);
1986                 p->group_leader = p;
1987                 p->tgid = p->pid;
1988         }
1989
1990         p->nr_dirtied = 0;
1991         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1992         p->dirty_paused_when = 0;
1993
1994         p->pdeath_signal = 0;
1995         INIT_LIST_HEAD(&p->thread_group);
1996         p->task_works = NULL;
1997
1998         cgroup_threadgroup_change_begin(current);
1999         /*
2000          * Ensure that the cgroup subsystem policies allow the new process to be
2001          * forked. It should be noted the the new process's css_set can be changed
2002          * between here and cgroup_post_fork() if an organisation operation is in
2003          * progress.
2004          */
2005         retval = cgroup_can_fork(p);
2006         if (retval)
2007                 goto bad_fork_free_pid;
2008
2009         /*
2010          * From this point on we must avoid any synchronous user-space
2011          * communication until we take the tasklist-lock. In particular, we do
2012          * not want user-space to be able to predict the process start-time by
2013          * stalling fork(2) after we recorded the start_time but before it is
2014          * visible to the system.
2015          */
2016
2017         p->start_time = ktime_get_ns();
2018         p->real_start_time = ktime_get_boot_ns();
2019
2020         /*
2021          * Make it visible to the rest of the system, but dont wake it up yet.
2022          * Need tasklist lock for parent etc handling!
2023          */
2024         write_lock_irq(&tasklist_lock);
2025
2026         /* CLONE_PARENT re-uses the old parent */
2027         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
2028                 p->real_parent = current->real_parent;
2029                 p->parent_exec_id = current->parent_exec_id;
2030         } else {
2031                 p->real_parent = current;
2032                 p->parent_exec_id = current->self_exec_id;
2033         }
2034
2035         klp_copy_process(p);
2036
2037         spin_lock(&current->sighand->siglock);
2038
2039         /*
2040          * Copy seccomp details explicitly here, in case they were changed
2041          * before holding sighand lock.
2042          */
2043         copy_seccomp(p);
2044
2045         rseq_fork(p, clone_flags);
2046
2047         /* Don't start children in a dying pid namespace */
2048         if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
2049                 retval = -ENOMEM;
2050                 goto bad_fork_cancel_cgroup;
2051         }
2052
2053         /* Let kill terminate clone/fork in the middle */
2054         if (fatal_signal_pending(current)) {
2055                 retval = -EINTR;
2056                 goto bad_fork_cancel_cgroup;
2057         }
2058
2059
2060         init_task_pid_links(p);
2061         if (likely(p->pid)) {
2062                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
2063
2064                 init_task_pid(p, PIDTYPE_PID, pid);
2065                 if (thread_group_leader(p)) {
2066                         init_task_pid(p, PIDTYPE_TGID, pid);
2067                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
2068                         init_task_pid(p, PIDTYPE_SID, task_session(current));
2069
2070                         if (is_child_reaper(pid)) {
2071                                 ns_of_pid(pid)->child_reaper = p;
2072                                 p->signal->flags |= SIGNAL_UNKILLABLE;
2073                         }
2074                         p->signal->shared_pending.signal = delayed.signal;
2075                         p->signal->tty = tty_kref_get(current->signal->tty);
2076                         /*
2077                          * Inherit has_child_subreaper flag under the same
2078                          * tasklist_lock with adding child to the process tree
2079                          * for propagate_has_child_subreaper optimization.
2080                          */
2081                         p->signal->has_child_subreaper = p->real_parent->signal->has_child_subreaper ||
2082                                                          p->real_parent->signal->is_child_subreaper;
2083                         list_add_tail(&p->sibling, &p->real_parent->children);
2084                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
2085                         attach_pid(p, PIDTYPE_TGID);
2086                         attach_pid(p, PIDTYPE_PGID);
2087                         attach_pid(p, PIDTYPE_SID);
2088                         __this_cpu_inc(process_counts);
2089                 } else {
2090                         current->signal->nr_threads++;
2091                         atomic_inc(&current->signal->live);
2092                         refcount_inc(&current->signal->sigcnt);
2093                         task_join_group_stop(p);
2094                         list_add_tail_rcu(&p->thread_group,
2095                                           &p->group_leader->thread_group);
2096                         list_add_tail_rcu(&p->thread_node,
2097                                           &p->signal->thread_head);
2098                 }
2099                 attach_pid(p, PIDTYPE_PID);
2100                 nr_threads++;
2101         }
2102         total_forks++;
2103         hlist_del_init(&delayed.node);
2104         spin_unlock(&current->sighand->siglock);
2105         syscall_tracepoint_update(p);
2106         write_unlock_irq(&tasklist_lock);
2107
2108         proc_fork_connector(p);
2109         cgroup_post_fork(p);
2110         cgroup_threadgroup_change_end(current);
2111         perf_event_fork(p);
2112
2113         trace_task_newtask(p, clone_flags);
2114         uprobe_copy_process(p, clone_flags);
2115
2116         return p;
2117
2118 bad_fork_cancel_cgroup:
2119         spin_unlock(&current->sighand->siglock);
2120         write_unlock_irq(&tasklist_lock);
2121         cgroup_cancel_fork(p);
2122 bad_fork_free_pid:
2123         cgroup_threadgroup_change_end(current);
2124         if (pid != &init_struct_pid)
2125                 free_pid(pid);
2126 bad_fork_cleanup_thread:
2127         exit_thread(p);
2128 bad_fork_cleanup_io:
2129         if (p->io_context)
2130                 exit_io_context(p);
2131 bad_fork_cleanup_namespaces:
2132         exit_task_namespaces(p);
2133 bad_fork_cleanup_mm:
2134         if (p->mm)
2135                 mmput(p->mm);
2136 bad_fork_cleanup_signal:
2137         if (!(clone_flags & CLONE_THREAD))
2138                 free_signal_struct(p->signal);
2139 bad_fork_cleanup_sighand:
2140         __cleanup_sighand(p->sighand);
2141 bad_fork_cleanup_fs:
2142         exit_fs(p); /* blocking */
2143 bad_fork_cleanup_files:
2144         exit_files(p); /* blocking */
2145 bad_fork_cleanup_semundo:
2146         exit_sem(p);
2147 bad_fork_cleanup_security:
2148         security_task_free(p);
2149 bad_fork_cleanup_audit:
2150         audit_free(p);
2151 bad_fork_cleanup_perf:
2152         perf_event_free_task(p);
2153 bad_fork_cleanup_policy:
2154         lockdep_free_task(p);
2155 #ifdef CONFIG_NUMA
2156         mpol_put(p->mempolicy);
2157 bad_fork_cleanup_threadgroup_lock:
2158 #endif
2159         delayacct_tsk_free(p);
2160 bad_fork_cleanup_count:
2161         atomic_dec(&p->cred->user->processes);
2162         exit_creds(p);
2163 bad_fork_free:
2164         p->state = TASK_DEAD;
2165         put_task_stack(p);
2166         free_task(p);
2167 fork_out:
2168         spin_lock_irq(&current->sighand->siglock);
2169         hlist_del_init(&delayed.node);
2170         spin_unlock_irq(&current->sighand->siglock);
2171         return ERR_PTR(retval);
2172 }
2173
2174 static inline void init_idle_pids(struct task_struct *idle)
2175 {
2176         enum pid_type type;
2177
2178         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
2179                 INIT_HLIST_NODE(&idle->pid_links[type]); /* not really needed */
2180                 init_task_pid(idle, type, &init_struct_pid);
2181         }
2182 }
2183
2184 struct task_struct *fork_idle(int cpu)
2185 {
2186         struct task_struct *task;
2187         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
2188                             cpu_to_node(cpu));
2189         if (!IS_ERR(task)) {
2190                 init_idle_pids(task);
2191                 init_idle(task, cpu);
2192         }
2193
2194         return task;
2195 }
2196
2197 struct mm_struct *copy_init_mm(void)
2198 {
2199         return dup_mm(NULL, &init_mm);
2200 }
2201
2202 /*
2203  *  Ok, this is the main fork-routine.
2204  *
2205  * It copies the process, and if successful kick-starts
2206  * it and waits for it to finish using the VM if required.
2207  */
2208 long _do_fork(unsigned long clone_flags,
2209               unsigned long stack_start,
2210               unsigned long stack_size,
2211               int __user *parent_tidptr,
2212               int __user *child_tidptr,
2213               unsigned long tls)
2214 {
2215         struct completion vfork;
2216         struct pid *pid;
2217         struct task_struct *p;
2218         int trace = 0;
2219         long nr;
2220
2221         /*
2222          * Determine whether and which event to report to ptracer.  When
2223          * called from kernel_thread or CLONE_UNTRACED is explicitly
2224          * requested, no event is reported; otherwise, report if the event
2225          * for the type of forking is enabled.
2226          */
2227         if (!(clone_flags & CLONE_UNTRACED)) {
2228                 if (clone_flags & CLONE_VFORK)
2229                         trace = PTRACE_EVENT_VFORK;
2230                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
2231                         trace = PTRACE_EVENT_CLONE;
2232                 else
2233                         trace = PTRACE_EVENT_FORK;
2234
2235                 if (likely(!ptrace_event_enabled(current, trace)))
2236                         trace = 0;
2237         }
2238
2239         p = copy_process(clone_flags, stack_start, stack_size,
2240                          child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
2241         add_latent_entropy();
2242
2243         if (IS_ERR(p))
2244                 return PTR_ERR(p);
2245
2246         /*
2247          * Do this prior waking up the new thread - the thread pointer
2248          * might get invalid after that point, if the thread exits quickly.
2249          */
2250         trace_sched_process_fork(current, p);
2251
2252         pid = get_task_pid(p, PIDTYPE_PID);
2253         nr = pid_vnr(pid);
2254
2255         if (clone_flags & CLONE_PARENT_SETTID)
2256                 put_user(nr, parent_tidptr);
2257
2258         if (clone_flags & CLONE_VFORK) {
2259                 p->vfork_done = &vfork;
2260                 init_completion(&vfork);
2261                 get_task_struct(p);
2262         }
2263
2264         wake_up_new_task(p);
2265
2266         /* forking complete and child started to run, tell ptracer */
2267         if (unlikely(trace))
2268                 ptrace_event_pid(trace, pid);
2269
2270         if (clone_flags & CLONE_VFORK) {
2271                 if (!wait_for_vfork_done(p, &vfork))
2272                         ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
2273         }
2274
2275         put_pid(pid);
2276         return nr;
2277 }
2278
2279 #ifndef CONFIG_HAVE_COPY_THREAD_TLS
2280 /* For compatibility with architectures that call do_fork directly rather than
2281  * using the syscall entry points below. */
2282 long do_fork(unsigned long clone_flags,
2283               unsigned long stack_start,
2284               unsigned long stack_size,
2285               int __user *parent_tidptr,
2286               int __user *child_tidptr)
2287 {
2288         return _do_fork(clone_flags, stack_start, stack_size,
2289                         parent_tidptr, child_tidptr, 0);
2290 }
2291 #endif
2292
2293 /*
2294  * Create a kernel thread.
2295  */
2296 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
2297 {
2298         return _do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
2299                 (unsigned long)arg, NULL, NULL, 0);
2300 }
2301
2302 #ifdef __ARCH_WANT_SYS_FORK
2303 SYSCALL_DEFINE0(fork)
2304 {
2305 #ifdef CONFIG_MMU
2306         return _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0);
2307 #else
2308         /* can not support in nommu mode */
2309         return -EINVAL;
2310 #endif
2311 }
2312 #endif
2313
2314 #ifdef __ARCH_WANT_SYS_VFORK
2315 SYSCALL_DEFINE0(vfork)
2316 {
2317         return _do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
2318                         0, NULL, NULL, 0);
2319 }
2320 #endif
2321
2322 #ifdef __ARCH_WANT_SYS_CLONE
2323 #ifdef CONFIG_CLONE_BACKWARDS
2324 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
2325                  int __user *, parent_tidptr,
2326                  unsigned long, tls,
2327                  int __user *, child_tidptr)
2328 #elif defined(CONFIG_CLONE_BACKWARDS2)
2329 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
2330                  int __user *, parent_tidptr,
2331                  int __user *, child_tidptr,
2332                  unsigned long, tls)
2333 #elif defined(CONFIG_CLONE_BACKWARDS3)
2334 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
2335                 int, stack_size,
2336                 int __user *, parent_tidptr,
2337                 int __user *, child_tidptr,
2338                 unsigned long, tls)
2339 #else
2340 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
2341                  int __user *, parent_tidptr,
2342                  int __user *, child_tidptr,
2343                  unsigned long, tls)
2344 #endif
2345 {
2346         return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls);
2347 }
2348 #endif
2349
2350 void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
2351 {
2352         struct task_struct *leader, *parent, *child;
2353         int res;
2354
2355         read_lock(&tasklist_lock);
2356         leader = top = top->group_leader;
2357 down:
2358         for_each_thread(leader, parent) {
2359                 list_for_each_entry(child, &parent->children, sibling) {
2360                         res = visitor(child, data);
2361                         if (res) {
2362                                 if (res < 0)
2363                                         goto out;
2364                                 leader = child;
2365                                 goto down;
2366                         }
2367 up:
2368                         ;
2369                 }
2370         }
2371
2372         if (leader != top) {
2373                 child = leader;
2374                 parent = child->real_parent;
2375                 leader = parent->group_leader;
2376                 goto up;
2377         }
2378 out:
2379         read_unlock(&tasklist_lock);
2380 }
2381
2382 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
2383 #define ARCH_MIN_MMSTRUCT_ALIGN 0
2384 #endif
2385
2386 static void sighand_ctor(void *data)
2387 {
2388         struct sighand_struct *sighand = data;
2389
2390         spin_lock_init(&sighand->siglock);
2391         init_waitqueue_head(&sighand->signalfd_wqh);
2392 }
2393
2394 void __init proc_caches_init(void)
2395 {
2396         unsigned int mm_size;
2397
2398         sighand_cachep = kmem_cache_create("sighand_cache",
2399                         sizeof(struct sighand_struct), 0,
2400                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
2401                         SLAB_ACCOUNT, sighand_ctor);
2402         signal_cachep = kmem_cache_create("signal_cache",
2403                         sizeof(struct signal_struct), 0,
2404                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2405                         NULL);
2406         files_cachep = kmem_cache_create("files_cache",
2407                         sizeof(struct files_struct), 0,
2408                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2409                         NULL);
2410         fs_cachep = kmem_cache_create("fs_cache",
2411                         sizeof(struct fs_struct), 0,
2412                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2413                         NULL);
2414
2415         /*
2416          * The mm_cpumask is located at the end of mm_struct, and is
2417          * dynamically sized based on the maximum CPU number this system
2418          * can have, taking hotplug into account (nr_cpu_ids).
2419          */
2420         mm_size = sizeof(struct mm_struct) + cpumask_size();
2421
2422         mm_cachep = kmem_cache_create_usercopy("mm_struct",
2423                         mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
2424                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2425                         offsetof(struct mm_struct, saved_auxv),
2426                         sizeof_field(struct mm_struct, saved_auxv),
2427                         NULL);
2428         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
2429         mmap_init();
2430         nsproxy_cache_init();
2431 }
2432
2433 /*
2434  * Check constraints on flags passed to the unshare system call.
2435  */
2436 static int check_unshare_flags(unsigned long unshare_flags)
2437 {
2438         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
2439                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
2440                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
2441                                 CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWCGROUP))
2442                 return -EINVAL;
2443         /*
2444          * Not implemented, but pretend it works if there is nothing
2445          * to unshare.  Note that unsharing the address space or the
2446          * signal handlers also need to unshare the signal queues (aka
2447          * CLONE_THREAD).
2448          */
2449         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
2450                 if (!thread_group_empty(current))
2451                         return -EINVAL;
2452         }
2453         if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
2454                 if (refcount_read(&current->sighand->count) > 1)
2455                         return -EINVAL;
2456         }
2457         if (unshare_flags & CLONE_VM) {
2458                 if (!current_is_single_threaded())
2459                         return -EINVAL;
2460         }
2461
2462         return 0;
2463 }
2464
2465 /*
2466  * Unshare the filesystem structure if it is being shared
2467  */
2468 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
2469 {
2470         struct fs_struct *fs = current->fs;
2471
2472         if (!(unshare_flags & CLONE_FS) || !fs)
2473                 return 0;
2474
2475         /* don't need lock here; in the worst case we'll do useless copy */
2476         if (fs->users == 1)
2477                 return 0;
2478
2479         *new_fsp = copy_fs_struct(fs);
2480         if (!*new_fsp)
2481                 return -ENOMEM;
2482
2483         return 0;
2484 }
2485
2486 /*
2487  * Unshare file descriptor table if it is being shared
2488  */
2489 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
2490 {
2491         struct files_struct *fd = current->files;
2492         int error = 0;
2493
2494         if ((unshare_flags & CLONE_FILES) &&
2495             (fd && atomic_read(&fd->count) > 1)) {
2496                 *new_fdp = dup_fd(fd, &error);
2497                 if (!*new_fdp)
2498                         return error;
2499         }
2500
2501         return 0;
2502 }
2503
2504 /*
2505  * unshare allows a process to 'unshare' part of the process
2506  * context which was originally shared using clone.  copy_*
2507  * functions used by do_fork() cannot be used here directly
2508  * because they modify an inactive task_struct that is being
2509  * constructed. Here we are modifying the current, active,
2510  * task_struct.
2511  */
2512 int ksys_unshare(unsigned long unshare_flags)
2513 {
2514         struct fs_struct *fs, *new_fs = NULL;
2515         struct files_struct *fd, *new_fd = NULL;
2516         struct cred *new_cred = NULL;
2517         struct nsproxy *new_nsproxy = NULL;
2518         int do_sysvsem = 0;
2519         int err;
2520
2521         /*
2522          * If unsharing a user namespace must also unshare the thread group
2523          * and unshare the filesystem root and working directories.
2524          */
2525         if (unshare_flags & CLONE_NEWUSER)
2526                 unshare_flags |= CLONE_THREAD | CLONE_FS;
2527         /*
2528          * If unsharing vm, must also unshare signal handlers.
2529          */
2530         if (unshare_flags & CLONE_VM)
2531                 unshare_flags |= CLONE_SIGHAND;
2532         /*
2533          * If unsharing a signal handlers, must also unshare the signal queues.
2534          */
2535         if (unshare_flags & CLONE_SIGHAND)
2536                 unshare_flags |= CLONE_THREAD;
2537         /*
2538          * If unsharing namespace, must also unshare filesystem information.
2539          */
2540         if (unshare_flags & CLONE_NEWNS)
2541                 unshare_flags |= CLONE_FS;
2542
2543         err = check_unshare_flags(unshare_flags);
2544         if (err)
2545                 goto bad_unshare_out;
2546         /*
2547          * CLONE_NEWIPC must also detach from the undolist: after switching
2548          * to a new ipc namespace, the semaphore arrays from the old
2549          * namespace are unreachable.
2550          */
2551         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
2552                 do_sysvsem = 1;
2553         err = unshare_fs(unshare_flags, &new_fs);
2554         if (err)
2555                 goto bad_unshare_out;
2556         err = unshare_fd(unshare_flags, &new_fd);
2557         if (err)
2558                 goto bad_unshare_cleanup_fs;
2559         err = unshare_userns(unshare_flags, &new_cred);
2560         if (err)
2561                 goto bad_unshare_cleanup_fd;
2562         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
2563                                          new_cred, new_fs);
2564         if (err)
2565                 goto bad_unshare_cleanup_cred;
2566
2567         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
2568                 if (do_sysvsem) {
2569                         /*
2570                          * CLONE_SYSVSEM is equivalent to sys_exit().
2571                          */
2572                         exit_sem(current);
2573                 }
2574                 if (unshare_flags & CLONE_NEWIPC) {
2575                         /* Orphan segments in old ns (see sem above). */
2576                         exit_shm(current);
2577                         shm_init_task(current);
2578                 }
2579
2580                 if (new_nsproxy)
2581                         switch_task_namespaces(current, new_nsproxy);
2582
2583                 task_lock(current);
2584
2585                 if (new_fs) {
2586                         fs = current->fs;
2587                         spin_lock(&fs->lock);
2588                         current->fs = new_fs;
2589                         if (--fs->users)
2590                                 new_fs = NULL;
2591                         else
2592                                 new_fs = fs;
2593                         spin_unlock(&fs->lock);
2594                 }
2595
2596                 if (new_fd) {
2597                         fd = current->files;
2598                         current->files = new_fd;
2599                         new_fd = fd;
2600                 }
2601
2602                 task_unlock(current);
2603
2604                 if (new_cred) {
2605                         /* Install the new user namespace */
2606                         commit_creds(new_cred);
2607                         new_cred = NULL;
2608                 }
2609         }
2610
2611         perf_event_namespaces(current);
2612
2613 bad_unshare_cleanup_cred:
2614         if (new_cred)
2615                 put_cred(new_cred);
2616 bad_unshare_cleanup_fd:
2617         if (new_fd)
2618                 put_files_struct(new_fd);
2619
2620 bad_unshare_cleanup_fs:
2621         if (new_fs)
2622                 free_fs_struct(new_fs);
2623
2624 bad_unshare_out:
2625         return err;
2626 }
2627
2628 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
2629 {
2630         return ksys_unshare(unshare_flags);
2631 }
2632
2633 /*
2634  *      Helper to unshare the files of the current task.
2635  *      We don't want to expose copy_files internals to
2636  *      the exec layer of the kernel.
2637  */
2638
2639 int unshare_files(struct files_struct **displaced)
2640 {
2641         struct task_struct *task = current;
2642         struct files_struct *copy = NULL;
2643         int error;
2644
2645         error = unshare_fd(CLONE_FILES, &copy);
2646         if (error || !copy) {
2647                 *displaced = NULL;
2648                 return error;
2649         }
2650         *displaced = task->files;
2651         task_lock(task);
2652         task->files = copy;
2653         task_unlock(task);
2654         return 0;
2655 }
2656
2657 int sysctl_max_threads(struct ctl_table *table, int write,
2658                        void __user *buffer, size_t *lenp, loff_t *ppos)
2659 {
2660         struct ctl_table t;
2661         int ret;
2662         int threads = max_threads;
2663         int min = MIN_THREADS;
2664         int max = MAX_THREADS;
2665
2666         t = *table;
2667         t.data = &threads;
2668         t.extra1 = &min;
2669         t.extra2 = &max;
2670
2671         ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
2672         if (ret || !write)
2673                 return ret;
2674
2675         set_max_threads(threads);
2676
2677         return 0;
2678 }