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 }
 819
 820 int __weak arch_dup_task_struct(struct task_struct *dst,
 821                                                struct task_struct *src)
 822 {
 823         *dst = *src;
 824         return 0;
 825 }
 826
 827 void set_task_stack_end_magic(struct task_struct *tsk)
 828 {
 829         unsigned long *stackend;
 830
 831         stackend = end_of_stack(tsk);
 832         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 833 }
 834
 835 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 836 {
 837         struct task_struct *tsk;
 838         unsigned long *stack;
 839         struct vm_struct *stack_vm_area __maybe_unused;
 840         int err;
 841
 842         if (node == NUMA_NO_NODE)
 843                 node = tsk_fork_get_node(orig);
 844         tsk = alloc_task_struct_node(node);
 845         if (!tsk)
 846                 return NULL;
 847
 848         stack = alloc_thread_stack_node(tsk, node);
 849         if (!stack)
 850                 goto free_tsk;
 851
 852         if (memcg_charge_kernel_stack(tsk))
 853                 goto free_stack;
 854
 855         stack_vm_area = task_stack_vm_area(tsk);
 856
 857         err = arch_dup_task_struct(tsk, orig);
 858
 859         /*
 860          * arch_dup_task_struct() clobbers the stack-related fields.  Make
 861          * sure they're properly initialized before using any stack-related
 862          * functions again.
 863          */
 864         tsk->stack = stack;
 865 #ifdef CONFIG_VMAP_STACK
 866         tsk->stack_vm_area = stack_vm_area;
 867 #endif
 868 #ifdef CONFIG_THREAD_INFO_IN_TASK
 869         refcount_set(&tsk->stack_refcount, 1);
 870 #endif
 871
 872         if (err)
 873                 goto free_stack;
 874
 875 #ifdef CONFIG_SECCOMP
 876         /*
 877          * We must handle setting up seccomp filters once we're under
 878          * the sighand lock in case orig has changed between now and
 879          * then. Until then, filter must be NULL to avoid messing up
 880          * the usage counts on the error path calling free_task.
 881          */
 882         tsk->seccomp.filter = NULL;
 883 #endif
 884
 885         setup_thread_stack(tsk, orig);
 886         clear_user_return_notifier(tsk);
 887         clear_tsk_need_resched(tsk);
 888         set_task_stack_end_magic(tsk);
 889
 890 #ifdef CONFIG_STACKPROTECTOR
 891         tsk->stack_canary = get_random_canary();
 892 #endif
 893
 894         /*
 895          * One for us, one for whoever does the "release_task()" (usually
 896          * parent)
 897          */
 898         refcount_set(&tsk->usage, 2);
 899 #ifdef CONFIG_BLK_DEV_IO_TRACE
 900         tsk->btrace_seq = 0;
 901 #endif
 902         tsk->splice_pipe = NULL;
 903         tsk->task_frag.page = NULL;
 904         tsk->wake_q.next = NULL;
 905
 906         account_kernel_stack(tsk, 1);
 907
 908         kcov_task_init(tsk);
 909
 910 #ifdef CONFIG_FAULT_INJECTION
 911         tsk->fail_nth = 0;
 912 #endif
 913
 914 #ifdef CONFIG_BLK_CGROUP
 915         tsk->throttle_queue = NULL;
 916         tsk->use_memdelay = 0;
 917 #endif
 918
 919 #ifdef CONFIG_MEMCG
 920         tsk->active_memcg = NULL;
 921 #endif
 922         return tsk;
 923
 924 free_stack:
 925         free_thread_stack(tsk);
 926 free_tsk:
 927         free_task_struct(tsk);
 928         return NULL;
 929 }
 930
 931 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 932
 933 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 934
 935 static int __init coredump_filter_setup(char *s)
 936 {
 937         default_dump_filter =
 938                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 939                 MMF_DUMP_FILTER_MASK;
 940         return 1;
 941 }
 942
 943 __setup("coredump_filter=", coredump_filter_setup);
 944
 945 #include <linux/init_task.h>
 946
 947 static void mm_init_aio(struct mm_struct *mm)
 948 {
 949 #ifdef CONFIG_AIO
 950         spin_lock_init(&mm->ioctx_lock);
 951         mm->ioctx_table = NULL;
 952 #endif
 953 }
 954
 955 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
 956 {
 957 #ifdef CONFIG_MEMCG
 958         mm->owner = p;
 959 #endif
 960 }
 961
 962 static void mm_init_uprobes_state(struct mm_struct *mm)
 963 {
 964 #ifdef CONFIG_UPROBES
 965         mm->uprobes_state.xol_area = NULL;
 966 #endif
 967 }
 968
 969 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 970         struct user_namespace *user_ns)
 971 {
 972         mm->mmap = NULL;
 973         mm->mm_rb = RB_ROOT;
 974         mm->vmacache_seqnum = 0;
 975         atomic_set(&mm->mm_users, 1);
 976         atomic_set(&mm->mm_count, 1);
 977         init_rwsem(&mm->mmap_sem);
 978         INIT_LIST_HEAD(&mm->mmlist);
 979         mm->core_state = NULL;
 980         mm_pgtables_bytes_init(mm);
 981         mm->map_count = 0;
 982         mm->locked_vm = 0;
 983         atomic64_set(&mm->pinned_vm, 0);
 984         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 985         spin_lock_init(&mm->page_table_lock);
 986         spin_lock_init(&mm->arg_lock);
 987         mm_init_cpumask(mm);
 988         mm_init_aio(mm);
 989         mm_init_owner(mm, p);
 990         RCU_INIT_POINTER(mm->exe_file, NULL);
 991         mmu_notifier_mm_init(mm);
 992         hmm_mm_init(mm);
 993         init_tlb_flush_pending(mm);
 994 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 995         mm->pmd_huge_pte = NULL;
 996 #endif
 997         mm_init_uprobes_state(mm);
 998
 999         if (current->mm) {
1000                 mm->flags = current->mm->flags & MMF_INIT_MASK;
1001                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
1002         } else {
1003                 mm->flags = default_dump_filter;
1004                 mm->def_flags = 0;
1005         }
1006
1007         if (mm_alloc_pgd(mm))
1008                 goto fail_nopgd;
1009
1010         if (init_new_context(p, mm))
1011                 goto fail_nocontext;
1012
1013         mm->user_ns = get_user_ns(user_ns);
1014         return mm;
1015
1016 fail_nocontext:
1017         mm_free_pgd(mm);
1018 fail_nopgd:
1019         free_mm(mm);
1020         return NULL;
1021 }
1022
1023 /*
1024  * Allocate and initialize an mm_struct.
1025  */
1026 struct mm_struct *mm_alloc(void)
1027 {
1028         struct mm_struct *mm;
1029
1030         mm = allocate_mm();
1031         if (!mm)
1032                 return NULL;
1033
1034         memset(mm, 0, sizeof(*mm));
1035         return mm_init(mm, current, current_user_ns());
1036 }
1037
1038 static inline void __mmput(struct mm_struct *mm)
1039 {
1040         VM_BUG_ON(atomic_read(&mm->mm_users));
1041
1042         uprobe_clear_state(mm);
1043         exit_aio(mm);
1044         ksm_exit(mm);
1045         khugepaged_exit(mm); /* must run before exit_mmap */
1046         exit_mmap(mm);
1047         mm_put_huge_zero_page(mm);
1048         set_mm_exe_file(mm, NULL);
1049         if (!list_empty(&mm->mmlist)) {
1050                 spin_lock(&mmlist_lock);
1051                 list_del(&mm->mmlist);
1052                 spin_unlock(&mmlist_lock);
1053         }
1054         if (mm->binfmt)
1055                 module_put(mm->binfmt->module);
1056         mmdrop(mm);
1057 }
1058
1059 /*
1060  * Decrement the use count and release all resources for an mm.
1061  */
1062 void mmput(struct mm_struct *mm)
1063 {
1064         might_sleep();
1065
1066         if (atomic_dec_and_test(&mm->mm_users))
1067                 __mmput(mm);
1068 }
1069 EXPORT_SYMBOL_GPL(mmput);
1070
1071 #ifdef CONFIG_MMU
1072 static void mmput_async_fn(struct work_struct *work)
1073 {
1074         struct mm_struct *mm = container_of(work, struct mm_struct,
1075                                             async_put_work);
1076
1077         __mmput(mm);
1078 }
1079
1080 void mmput_async(struct mm_struct *mm)
1081 {
1082         if (atomic_dec_and_test(&mm->mm_users)) {
1083                 INIT_WORK(&mm->async_put_work, mmput_async_fn);
1084                 schedule_work(&mm->async_put_work);
1085         }
1086 }
1087 #endif
1088
1089 /**
1090  * set_mm_exe_file - change a reference to the mm's executable file
1091  *
1092  * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
1093  *
1094  * Main users are mmput() and sys_execve(). Callers prevent concurrent
1095  * invocations: in mmput() nobody alive left, in execve task is single
1096  * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
1097  * mm->exe_file, but does so without using set_mm_exe_file() in order
1098  * to do avoid the need for any locks.
1099  */
1100 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
1101 {
1102         struct file *old_exe_file;
1103
1104         /*
1105          * It is safe to dereference the exe_file without RCU as
1106          * this function is only called if nobody else can access
1107          * this mm -- see comment above for justification.
1108          */
1109         old_exe_file = rcu_dereference_raw(mm->exe_file);
1110
1111         if (new_exe_file)
1112                 get_file(new_exe_file);
1113         rcu_assign_pointer(mm->exe_file, new_exe_file);
1114         if (old_exe_file)
1115                 fput(old_exe_file);
1116 }
1117
1118 /**
1119  * get_mm_exe_file - acquire a reference to the mm's executable file
1120  *
1121  * Returns %NULL if mm has no associated executable file.
1122  * User must release file via fput().
1123  */
1124 struct file *get_mm_exe_file(struct mm_struct *mm)
1125 {
1126         struct file *exe_file;
1127
1128         rcu_read_lock();
1129         exe_file = rcu_dereference(mm->exe_file);
1130         if (exe_file && !get_file_rcu(exe_file))
1131                 exe_file = NULL;
1132         rcu_read_unlock();
1133         return exe_file;
1134 }
1135 EXPORT_SYMBOL(get_mm_exe_file);
1136
1137 /**
1138  * get_task_exe_file - acquire a reference to the task's executable file
1139  *
1140  * Returns %NULL if task's mm (if any) has no associated executable file or
1141  * this is a kernel thread with borrowed mm (see the comment above get_task_mm).
1142  * User must release file via fput().
1143  */
1144 struct file *get_task_exe_file(struct task_struct *task)
1145 {
1146         struct file *exe_file = NULL;
1147         struct mm_struct *mm;
1148
1149         task_lock(task);
1150         mm = task->mm;
1151         if (mm) {
1152                 if (!(task->flags & PF_KTHREAD))
1153                         exe_file = get_mm_exe_file(mm);
1154         }
1155         task_unlock(task);
1156         return exe_file;
1157 }
1158 EXPORT_SYMBOL(get_task_exe_file);
1159
1160 /**
1161  * get_task_mm - acquire a reference to the task's mm
1162  *
1163  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
1164  * this kernel workthread has transiently adopted a user mm with use_mm,
1165  * to do its AIO) is not set and if so returns a reference to it, after
1166  * bumping up the use count.  User must release the mm via mmput()
1167  * after use.  Typically used by /proc and ptrace.
1168  */
1169 struct mm_struct *get_task_mm(struct task_struct *task)
1170 {
1171         struct mm_struct *mm;
1172
1173         task_lock(task);
1174         mm = task->mm;
1175         if (mm) {
1176                 if (task->flags & PF_KTHREAD)
1177                         mm = NULL;
1178                 else
1179                         mmget(mm);
1180         }
1181         task_unlock(task);
1182         return mm;
1183 }
1184 EXPORT_SYMBOL_GPL(get_task_mm);
1185
1186 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
1187 {
1188         struct mm_struct *mm;
1189         int err;
1190
1191         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
1192         if (err)
1193                 return ERR_PTR(err);
1194
1195         mm = get_task_mm(task);
1196         if (mm && mm != current->mm &&
1197                         !ptrace_may_access(task, mode)) {
1198                 mmput(mm);
1199                 mm = ERR_PTR(-EACCES);
1200         }
1201         mutex_unlock(&task->signal->cred_guard_mutex);
1202
1203         return mm;
1204 }
1205
1206 static void complete_vfork_done(struct task_struct *tsk)
1207 {
1208         struct completion *vfork;
1209
1210         task_lock(tsk);
1211         vfork = tsk->vfork_done;
1212         if (likely(vfork)) {
1213                 tsk->vfork_done = NULL;
1214                 complete(vfork);
1215         }
1216         task_unlock(tsk);
1217 }
1218
1219 static int wait_for_vfork_done(struct task_struct *child,
1220                                 struct completion *vfork)
1221 {
1222         int killed;
1223
1224         freezer_do_not_count();
1225         killed = wait_for_completion_killable(vfork);
1226         freezer_count();
1227
1228         if (killed) {
1229                 task_lock(child);
1230                 child->vfork_done = NULL;
1231                 task_unlock(child);
1232         }
1233
1234         put_task_struct(child);
1235         return killed;
1236 }
1237
1238 /* Please note the differences between mmput and mm_release.
1239  * mmput is called whenever we stop holding onto a mm_struct,
1240  * error success whatever.
1241  *
1242  * mm_release is called after a mm_struct has been removed
1243  * from the current process.
1244  *
1245  * This difference is important for error handling, when we
1246  * only half set up a mm_struct for a new process and need to restore
1247  * the old one.  Because we mmput the new mm_struct before
1248  * restoring the old one. . .
1249  * Eric Biederman 10 January 1998
1250  */
1251 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
1252 {
1253         /* Get rid of any futexes when releasing the mm */
1254 #ifdef CONFIG_FUTEX
1255         if (unlikely(tsk->robust_list)) {
1256                 exit_robust_list(tsk);
1257                 tsk->robust_list = NULL;
1258         }
1259 #ifdef CONFIG_COMPAT
1260         if (unlikely(tsk->compat_robust_list)) {
1261                 compat_exit_robust_list(tsk);
1262                 tsk->compat_robust_list = NULL;
1263         }
1264 #endif
1265         if (unlikely(!list_empty(&tsk->pi_state_list)))
1266                 exit_pi_state_list(tsk);
1267 #endif
1268
1269         uprobe_free_utask(tsk);
1270
1271         /* Get rid of any cached register state */
1272         deactivate_mm(tsk, mm);
1273
1274         /*
1275          * Signal userspace if we're not exiting with a core dump
1276          * because we want to leave the value intact for debugging
1277          * purposes.
1278          */
1279         if (tsk->clear_child_tid) {
1280                 if (!(tsk->signal->flags & SIGNAL_GROUP_COREDUMP) &&
1281                     atomic_read(&mm->mm_users) > 1) {
1282                         /*
1283                          * We don't check the error code - if userspace has
1284                          * not set up a proper pointer then tough luck.
1285                          */
1286                         put_user(0, tsk->clear_child_tid);
1287                         do_futex(tsk->clear_child_tid, FUTEX_WAKE,
1288                                         1, NULL, NULL, 0, 0);
1289                 }
1290                 tsk->clear_child_tid = NULL;
1291         }
1292
1293         /*
1294          * All done, finally we can wake up parent and return this mm to him.
1295          * Also kthread_stop() uses this completion for synchronization.
1296          */
1297         if (tsk->vfork_done)
1298                 complete_vfork_done(tsk);
1299 }
1300
1301 /*
1302  * Allocate a new mm structure and copy contents from the
1303  * mm structure of the passed in task structure.
1304  */
1305 static struct mm_struct *dup_mm(struct task_struct *tsk)
1306 {
1307         struct mm_struct *mm, *oldmm = current->mm;
1308         int err;
1309
1310         mm = allocate_mm();
1311         if (!mm)
1312                 goto fail_nomem;
1313
1314         memcpy(mm, oldmm, sizeof(*mm));
1315
1316         if (!mm_init(mm, tsk, mm->user_ns))
1317                 goto fail_nomem;
1318
1319         err = dup_mmap(mm, oldmm);
1320         if (err)
1321                 goto free_pt;
1322
1323         mm->hiwater_rss = get_mm_rss(mm);
1324         mm->hiwater_vm = mm->total_vm;
1325
1326         if (mm->binfmt && !try_module_get(mm->binfmt->module))
1327                 goto free_pt;
1328
1329         return mm;
1330
1331 free_pt:
1332         /* don't put binfmt in mmput, we haven't got module yet */
1333         mm->binfmt = NULL;
1334         mmput(mm);
1335
1336 fail_nomem:
1337         return NULL;
1338 }
1339
1340 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
1341 {
1342         struct mm_struct *mm, *oldmm;
1343         int retval;
1344
1345         tsk->min_flt = tsk->maj_flt = 0;
1346         tsk->nvcsw = tsk->nivcsw = 0;
1347 #ifdef CONFIG_DETECT_HUNG_TASK
1348         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
1349         tsk->last_switch_time = 0;
1350 #endif
1351
1352         tsk->mm = NULL;
1353         tsk->active_mm = NULL;
1354
1355         /*
1356          * Are we cloning a kernel thread?
1357          *
1358          * We need to steal a active VM for that..
1359          */
1360         oldmm = current->mm;
1361         if (!oldmm)
1362                 return 0;
1363
1364         /* initialize the new vmacache entries */
1365         vmacache_flush(tsk);
1366
1367         if (clone_flags & CLONE_VM) {
1368                 mmget(oldmm);
1369                 mm = oldmm;
1370                 goto good_mm;
1371         }
1372
1373         retval = -ENOMEM;
1374         mm = dup_mm(tsk);
1375         if (!mm)
1376                 goto fail_nomem;
1377
1378 good_mm:
1379         tsk->mm = mm;
1380         tsk->active_mm = mm;
1381         return 0;
1382
1383 fail_nomem:
1384         return retval;
1385 }
1386
1387 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
1388 {
1389         struct fs_struct *fs = current->fs;
1390         if (clone_flags & CLONE_FS) {
1391                 /* tsk->fs is already what we want */
1392                 spin_lock(&fs->lock);
1393                 if (fs->in_exec) {
1394                         spin_unlock(&fs->lock);
1395                         return -EAGAIN;
1396                 }
1397                 fs->users++;
1398                 spin_unlock(&fs->lock);
1399                 return 0;
1400         }
1401         tsk->fs = copy_fs_struct(fs);
1402         if (!tsk->fs)
1403                 return -ENOMEM;
1404         return 0;
1405 }
1406
1407 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
1408 {
1409         struct files_struct *oldf, *newf;
1410         int error = 0;
1411
1412         /*
1413          * A background process may not have any files ...
1414          */
1415         oldf = current->files;
1416         if (!oldf)
1417                 goto out;
1418
1419         if (clone_flags & CLONE_FILES) {
1420                 atomic_inc(&oldf->count);
1421                 goto out;
1422         }
1423
1424         newf = dup_fd(oldf, &error);
1425         if (!newf)
1426                 goto out;
1427
1428         tsk->files = newf;
1429         error = 0;
1430 out:
1431         return error;
1432 }
1433
1434 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
1435 {
1436 #ifdef CONFIG_BLOCK
1437         struct io_context *ioc = current->io_context;
1438         struct io_context *new_ioc;
1439
1440         if (!ioc)
1441                 return 0;
1442         /*
1443          * Share io context with parent, if CLONE_IO is set
1444          */
1445         if (clone_flags & CLONE_IO) {
1446                 ioc_task_link(ioc);
1447                 tsk->io_context = ioc;
1448         } else if (ioprio_valid(ioc->ioprio)) {
1449                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
1450                 if (unlikely(!new_ioc))
1451                         return -ENOMEM;
1452
1453                 new_ioc->ioprio = ioc->ioprio;
1454                 put_io_context(new_ioc);
1455         }
1456 #endif
1457         return 0;
1458 }
1459
1460 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1461 {
1462         struct sighand_struct *sig;
1463
1464         if (clone_flags & CLONE_SIGHAND) {
1465                 refcount_inc(&current->sighand->count);
1466                 return 0;
1467         }
1468         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1469         rcu_assign_pointer(tsk->sighand, sig);
1470         if (!sig)
1471                 return -ENOMEM;
1472
1473         refcount_set(&sig->count, 1);
1474         spin_lock_irq(&current->sighand->siglock);
1475         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1476         spin_unlock_irq(&current->sighand->siglock);
1477         return 0;
1478 }
1479
1480 void __cleanup_sighand(struct sighand_struct *sighand)
1481 {
1482         if (refcount_dec_and_test(&sighand->count)) {
1483                 signalfd_cleanup(sighand);
1484                 /*
1485                  * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it
1486                  * without an RCU grace period, see __lock_task_sighand().
1487                  */
1488                 kmem_cache_free(sighand_cachep, sighand);
1489         }
1490 }
1491
1492 #ifdef CONFIG_POSIX_TIMERS
1493 /*
1494  * Initialize POSIX timer handling for a thread group.
1495  */
1496 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1497 {
1498         unsigned long cpu_limit;
1499
1500         cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1501         if (cpu_limit != RLIM_INFINITY) {
1502                 sig->cputime_expires.prof_exp = cpu_limit * NSEC_PER_SEC;
1503                 sig->cputimer.running = true;
1504         }
1505
1506         /* The timer lists. */
1507         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1508         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1509         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1510 }
1511 #else
1512 static inline void posix_cpu_timers_init_group(struct signal_struct *sig) { }
1513 #endif
1514
1515 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1516 {
1517         struct signal_struct *sig;
1518
1519         if (clone_flags & CLONE_THREAD)
1520                 return 0;
1521
1522         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1523         tsk->signal = sig;
1524         if (!sig)
1525                 return -ENOMEM;
1526
1527         sig->nr_threads = 1;
1528         atomic_set(&sig->live, 1);
1529         refcount_set(&sig->sigcnt, 1);
1530
1531         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1532         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1533         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1534
1535         init_waitqueue_head(&sig->wait_chldexit);
1536         sig->curr_target = tsk;
1537         init_sigpending(&sig->shared_pending);
1538         INIT_HLIST_HEAD(&sig->multiprocess);
1539         seqlock_init(&sig->stats_lock);
1540         prev_cputime_init(&sig->prev_cputime);
1541
1542 #ifdef CONFIG_POSIX_TIMERS
1543         INIT_LIST_HEAD(&sig->posix_timers);
1544         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1545         sig->real_timer.function = it_real_fn;
1546 #endif
1547
1548         task_lock(current->group_leader);
1549         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1550         task_unlock(current->group_leader);
1551
1552         posix_cpu_timers_init_group(sig);
1553
1554         tty_audit_fork(sig);
1555         sched_autogroup_fork(sig);
1556
1557         sig->oom_score_adj = current->signal->oom_score_adj;
1558         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1559
1560         mutex_init(&sig->cred_guard_mutex);
1561
1562         return 0;
1563 }
1564
1565 static void copy_seccomp(struct task_struct *p)
1566 {
1567 #ifdef CONFIG_SECCOMP
1568         /*
1569          * Must be called with sighand->lock held, which is common to
1570          * all threads in the group. Holding cred_guard_mutex is not
1571          * needed because this new task is not yet running and cannot
1572          * be racing exec.
1573          */
1574         assert_spin_locked(&current->sighand->siglock);
1575
1576         /* Ref-count the new filter user, and assign it. */
1577         get_seccomp_filter(current);
1578         p->seccomp = current->seccomp;
1579
1580         /*
1581          * Explicitly enable no_new_privs here in case it got set
1582          * between the task_struct being duplicated and holding the
1583          * sighand lock. The seccomp state and nnp must be in sync.
1584          */
1585         if (task_no_new_privs(current))
1586                 task_set_no_new_privs(p);
1587
1588         /*
1589          * If the parent gained a seccomp mode after copying thread
1590          * flags and between before we held the sighand lock, we have
1591          * to manually enable the seccomp thread flag here.
1592          */
1593         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1594                 set_tsk_thread_flag(p, TIF_SECCOMP);
1595 #endif
1596 }
1597
1598 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1599 {
1600         current->clear_child_tid = tidptr;
1601
1602         return task_pid_vnr(current);
1603 }
1604
1605 static void rt_mutex_init_task(struct task_struct *p)
1606 {
1607         raw_spin_lock_init(&p->pi_lock);
1608 #ifdef CONFIG_RT_MUTEXES
1609         p->pi_waiters = RB_ROOT_CACHED;
1610         p->pi_top_task = NULL;
1611         p->pi_blocked_on = NULL;
1612 #endif
1613 }
1614
1615 #ifdef CONFIG_POSIX_TIMERS
1616 /*
1617  * Initialize POSIX timer handling for a single task.
1618  */
1619 static void posix_cpu_timers_init(struct task_struct *tsk)
1620 {
1621         tsk->cputime_expires.prof_exp = 0;
1622         tsk->cputime_expires.virt_exp = 0;
1623         tsk->cputime_expires.sched_exp = 0;
1624         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1625         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1626         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1627 }
1628 #else
1629 static inline void posix_cpu_timers_init(struct task_struct *tsk) { }
1630 #endif
1631
1632 static inline void init_task_pid_links(struct task_struct *task)
1633 {
1634         enum pid_type type;
1635
1636         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1637                 INIT_HLIST_NODE(&task->pid_links[type]);
1638         }
1639 }
1640
1641 static inline void
1642 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1643 {
1644         if (type == PIDTYPE_PID)
1645                 task->thread_pid = pid;
1646         else
1647                 task->signal->pids[type] = pid;
1648 }
1649
1650 static inline void rcu_copy_process(struct task_struct *p)
1651 {
1652 #ifdef CONFIG_PREEMPT_RCU
1653         p->rcu_read_lock_nesting = 0;
1654         p->rcu_read_unlock_special.s = 0;
1655         p->rcu_blocked_node = NULL;
1656         INIT_LIST_HEAD(&p->rcu_node_entry);
1657 #endif /* #ifdef CONFIG_PREEMPT_RCU */
1658 #ifdef CONFIG_TASKS_RCU
1659         p->rcu_tasks_holdout = false;
1660         INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
1661         p->rcu_tasks_idle_cpu = -1;
1662 #endif /* #ifdef CONFIG_TASKS_RCU */
1663 }
1664
1665 /*
1666  * This creates a new process as a copy of the old one,
1667  * but does not actually start it yet.
1668  *
1669  * It copies the registers, and all the appropriate
1670  * parts of the process environment (as per the clone
1671  * flags). The actual kick-off is left to the caller.
1672  */
1673 static __latent_entropy struct task_struct *copy_process(
1674                                         unsigned long clone_flags,
1675                                         unsigned long stack_start,
1676                                         unsigned long stack_size,
1677                                         int __user *child_tidptr,
1678                                         struct pid *pid,
1679                                         int trace,
1680                                         unsigned long tls,
1681                                         int node)
1682 {
1683         int retval;
1684         struct task_struct *p;
1685         struct multiprocess_signals delayed;
1686
1687         /*
1688          * Don't allow sharing the root directory with processes in a different
1689          * namespace
1690          */
1691         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1692                 return ERR_PTR(-EINVAL);
1693
1694         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1695                 return ERR_PTR(-EINVAL);
1696
1697         /*
1698          * Thread groups must share signals as well, and detached threads
1699          * can only be started up within the thread group.
1700          */
1701         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1702                 return ERR_PTR(-EINVAL);
1703
1704         /*
1705          * Shared signal handlers imply shared VM. By way of the above,
1706          * thread groups also imply shared VM. Blocking this case allows
1707          * for various simplifications in other code.
1708          */
1709         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1710                 return ERR_PTR(-EINVAL);
1711
1712         /*
1713          * Siblings of global init remain as zombies on exit since they are
1714          * not reaped by their parent (swapper). To solve this and to avoid
1715          * multi-rooted process trees, prevent global and container-inits
1716          * from creating siblings.
1717          */
1718         if ((clone_flags & CLONE_PARENT) &&
1719                                 current->signal->flags & SIGNAL_UNKILLABLE)
1720                 return ERR_PTR(-EINVAL);
1721
1722         /*
1723          * If the new process will be in a different pid or user namespace
1724          * do not allow it to share a thread group with the forking task.
1725          */
1726         if (clone_flags & CLONE_THREAD) {
1727                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1728                     (task_active_pid_ns(current) !=
1729                                 current->nsproxy->pid_ns_for_children))
1730                         return ERR_PTR(-EINVAL);
1731         }
1732
1733         /*
1734          * Force any signals received before this point to be delivered
1735          * before the fork happens.  Collect up signals sent to multiple
1736          * processes that happen during the fork and delay them so that
1737          * they appear to happen after the fork.
1738          */
1739         sigemptyset(&delayed.signal);
1740         INIT_HLIST_NODE(&delayed.node);
1741
1742         spin_lock_irq(&current->sighand->siglock);
1743         if (!(clone_flags & CLONE_THREAD))
1744                 hlist_add_head(&delayed.node, &current->signal->multiprocess);
1745         recalc_sigpending();
1746         spin_unlock_irq(&current->sighand->siglock);
1747         retval = -ERESTARTNOINTR;
1748         if (signal_pending(current))
1749                 goto fork_out;
1750
1751         retval = -ENOMEM;
1752         p = dup_task_struct(current, node);
1753         if (!p)
1754                 goto fork_out;
1755
1756         /*
1757          * This _must_ happen before we call free_task(), i.e. before we jump
1758          * to any of the bad_fork_* labels. This is to avoid freeing
1759          * p->set_child_tid which is (ab)used as a kthread's data pointer for
1760          * kernel threads (PF_KTHREAD).
1761          */
1762         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1763         /*
1764          * Clear TID on mm_release()?
1765          */
1766         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1767
1768         ftrace_graph_init_task(p);
1769
1770         rt_mutex_init_task(p);
1771
1772 #ifdef CONFIG_PROVE_LOCKING
1773         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1774         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1775 #endif
1776         retval = -EAGAIN;
1777         if (atomic_read(&p->real_cred->user->processes) >=
1778                         task_rlimit(p, RLIMIT_NPROC)) {
1779                 if (p->real_cred->user != INIT_USER &&
1780                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1781                         goto bad_fork_free;
1782         }
1783         current->flags &= ~PF_NPROC_EXCEEDED;
1784
1785         retval = copy_creds(p, clone_flags);
1786         if (retval < 0)
1787                 goto bad_fork_free;
1788
1789         /*
1790          * If multiple threads are within copy_process(), then this check
1791          * triggers too late. This doesn't hurt, the check is only there
1792          * to stop root fork bombs.
1793          */
1794         retval = -EAGAIN;
1795         if (nr_threads >= max_threads)
1796                 goto bad_fork_cleanup_count;
1797
1798         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1799         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE);
1800         p->flags |= PF_FORKNOEXEC;
1801         INIT_LIST_HEAD(&p->children);
1802         INIT_LIST_HEAD(&p->sibling);
1803         rcu_copy_process(p);
1804         p->vfork_done = NULL;
1805         spin_lock_init(&p->alloc_lock);
1806
1807         init_sigpending(&p->pending);
1808
1809         p->utime = p->stime = p->gtime = 0;
1810 #ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
1811         p->utimescaled = p->stimescaled = 0;
1812 #endif
1813         prev_cputime_init(&p->prev_cputime);
1814
1815 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1816         seqcount_init(&p->vtime.seqcount);
1817         p->vtime.starttime = 0;
1818         p->vtime.state = VTIME_INACTIVE;
1819 #endif
1820
1821 #if defined(SPLIT_RSS_COUNTING)
1822         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1823 #endif
1824
1825         p->default_timer_slack_ns = current->timer_slack_ns;
1826
1827 #ifdef CONFIG_PSI
1828         p->psi_flags = 0;
1829 #endif
1830
1831         task_io_accounting_init(&p->ioac);
1832         acct_clear_integrals(p);
1833
1834         posix_cpu_timers_init(p);
1835
1836         p->io_context = NULL;
1837         audit_set_context(p, NULL);
1838         cgroup_fork(p);
1839 #ifdef CONFIG_NUMA
1840         p->mempolicy = mpol_dup(p->mempolicy);
1841         if (IS_ERR(p->mempolicy)) {
1842                 retval = PTR_ERR(p->mempolicy);
1843                 p->mempolicy = NULL;
1844                 goto bad_fork_cleanup_threadgroup_lock;
1845         }
1846 #endif
1847 #ifdef CONFIG_CPUSETS
1848         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1849         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1850         seqcount_init(&p->mems_allowed_seq);
1851 #endif
1852 #ifdef CONFIG_TRACE_IRQFLAGS
1853         p->irq_events = 0;
1854         p->hardirqs_enabled = 0;
1855         p->hardirq_enable_ip = 0;
1856         p->hardirq_enable_event = 0;
1857         p->hardirq_disable_ip = _THIS_IP_;
1858         p->hardirq_disable_event = 0;
1859         p->softirqs_enabled = 1;
1860         p->softirq_enable_ip = _THIS_IP_;
1861         p->softirq_enable_event = 0;
1862         p->softirq_disable_ip = 0;
1863         p->softirq_disable_event = 0;
1864         p->hardirq_context = 0;
1865         p->softirq_context = 0;
1866 #endif
1867
1868         p->pagefault_disabled = 0;
1869
1870 #ifdef CONFIG_LOCKDEP
1871         p->lockdep_depth = 0; /* no locks held yet */
1872         p->curr_chain_key = 0;
1873         p->lockdep_recursion = 0;
1874         lockdep_init_task(p);
1875 #endif
1876
1877 #ifdef CONFIG_DEBUG_MUTEXES
1878         p->blocked_on = NULL; /* not blocked yet */
1879 #endif
1880 #ifdef CONFIG_BCACHE
1881         p->sequential_io        = 0;
1882         p->sequential_io_avg    = 0;
1883 #endif
1884
1885         /* Perform scheduler related setup. Assign this task to a CPU. */
1886         retval = sched_fork(clone_flags, p);
1887         if (retval)
1888                 goto bad_fork_cleanup_policy;
1889
1890         retval = perf_event_init_task(p);
1891         if (retval)
1892                 goto bad_fork_cleanup_policy;
1893         retval = audit_alloc(p);
1894         if (retval)
1895                 goto bad_fork_cleanup_perf;
1896         /* copy all the process information */
1897         shm_init_task(p);
1898         retval = security_task_alloc(p, clone_flags);
1899         if (retval)
1900                 goto bad_fork_cleanup_audit;
1901         retval = copy_semundo(clone_flags, p);
1902         if (retval)
1903                 goto bad_fork_cleanup_security;
1904         retval = copy_files(clone_flags, p);
1905         if (retval)
1906                 goto bad_fork_cleanup_semundo;
1907         retval = copy_fs(clone_flags, p);
1908         if (retval)
1909                 goto bad_fork_cleanup_files;
1910         retval = copy_sighand(clone_flags, p);
1911         if (retval)
1912                 goto bad_fork_cleanup_fs;
1913         retval = copy_signal(clone_flags, p);
1914         if (retval)
1915                 goto bad_fork_cleanup_sighand;
1916         retval = copy_mm(clone_flags, p);
1917         if (retval)
1918                 goto bad_fork_cleanup_signal;
1919         retval = copy_namespaces(clone_flags, p);
1920         if (retval)
1921                 goto bad_fork_cleanup_mm;
1922         retval = copy_io(clone_flags, p);
1923         if (retval)
1924                 goto bad_fork_cleanup_namespaces;
1925         retval = copy_thread_tls(clone_flags, stack_start, stack_size, p, tls);
1926         if (retval)
1927                 goto bad_fork_cleanup_io;
1928
1929         stackleak_task_init(p);
1930
1931         if (pid != &init_struct_pid) {
1932                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1933                 if (IS_ERR(pid)) {
1934                         retval = PTR_ERR(pid);
1935                         goto bad_fork_cleanup_thread;
1936                 }
1937         }
1938
1939 #ifdef CONFIG_BLOCK
1940         p->plug = NULL;
1941 #endif
1942 #ifdef CONFIG_FUTEX
1943         p->robust_list = NULL;
1944 #ifdef CONFIG_COMPAT
1945         p->compat_robust_list = NULL;
1946 #endif
1947         INIT_LIST_HEAD(&p->pi_state_list);
1948         p->pi_state_cache = NULL;
1949 #endif
1950         /*
1951          * sigaltstack should be cleared when sharing the same VM
1952          */
1953         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1954                 sas_ss_reset(p);
1955
1956         /*
1957          * Syscall tracing and stepping should be turned off in the
1958          * child regardless of CLONE_PTRACE.
1959          */
1960         user_disable_single_step(p);
1961         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1962 #ifdef TIF_SYSCALL_EMU
1963         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1964 #endif
1965         clear_all_latency_tracing(p);
1966
1967         /* ok, now we should be set up.. */
1968         p->pid = pid_nr(pid);
1969         if (clone_flags & CLONE_THREAD) {
1970                 p->exit_signal = -1;
1971                 p->group_leader = current->group_leader;
1972                 p->tgid = current->tgid;
1973         } else {
1974                 if (clone_flags & CLONE_PARENT)
1975                         p->exit_signal = current->group_leader->exit_signal;
1976                 else
1977                         p->exit_signal = (clone_flags & CSIGNAL);
1978                 p->group_leader = p;
1979                 p->tgid = p->pid;
1980         }
1981
1982         p->nr_dirtied = 0;
1983         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1984         p->dirty_paused_when = 0;
1985
1986         p->pdeath_signal = 0;
1987         INIT_LIST_HEAD(&p->thread_group);
1988         p->task_works = NULL;
1989
1990         cgroup_threadgroup_change_begin(current);
1991         /*
1992          * Ensure that the cgroup subsystem policies allow the new process to be
1993          * forked. It should be noted the the new process's css_set can be changed
1994          * between here and cgroup_post_fork() if an organisation operation is in
1995          * progress.
1996          */
1997         retval = cgroup_can_fork(p);
1998         if (retval)
1999                 goto bad_fork_free_pid;
2000
2001         /*
2002          * From this point on we must avoid any synchronous user-space
2003          * communication until we take the tasklist-lock. In particular, we do
2004          * not want user-space to be able to predict the process start-time by
2005          * stalling fork(2) after we recorded the start_time but before it is
2006          * visible to the system.
2007          */
2008
2009         p->start_time = ktime_get_ns();
2010         p->real_start_time = ktime_get_boot_ns();
2011
2012         /*
2013          * Make it visible to the rest of the system, but dont wake it up yet.
2014          * Need tasklist lock for parent etc handling!
2015          */
2016         write_lock_irq(&tasklist_lock);
2017
2018         /* CLONE_PARENT re-uses the old parent */
2019         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
2020                 p->real_parent = current->real_parent;
2021                 p->parent_exec_id = current->parent_exec_id;
2022         } else {
2023                 p->real_parent = current;
2024                 p->parent_exec_id = current->self_exec_id;
2025         }
2026
2027         klp_copy_process(p);
2028
2029         spin_lock(&current->sighand->siglock);
2030
2031         /*
2032          * Copy seccomp details explicitly here, in case they were changed
2033          * before holding sighand lock.
2034          */
2035         copy_seccomp(p);
2036
2037         rseq_fork(p, clone_flags);
2038
2039         /* Don't start children in a dying pid namespace */
2040         if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
2041                 retval = -ENOMEM;
2042                 goto bad_fork_cancel_cgroup;
2043         }
2044
2045         /* Let kill terminate clone/fork in the middle */
2046         if (fatal_signal_pending(current)) {
2047                 retval = -EINTR;
2048                 goto bad_fork_cancel_cgroup;
2049         }
2050
2051
2052         init_task_pid_links(p);
2053         if (likely(p->pid)) {
2054                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
2055
2056                 init_task_pid(p, PIDTYPE_PID, pid);
2057                 if (thread_group_leader(p)) {
2058                         init_task_pid(p, PIDTYPE_TGID, pid);
2059                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
2060                         init_task_pid(p, PIDTYPE_SID, task_session(current));
2061
2062                         if (is_child_reaper(pid)) {
2063                                 ns_of_pid(pid)->child_reaper = p;
2064                                 p->signal->flags |= SIGNAL_UNKILLABLE;
2065                         }
2066                         p->signal->shared_pending.signal = delayed.signal;
2067                         p->signal->tty = tty_kref_get(current->signal->tty);
2068                         /*
2069                          * Inherit has_child_subreaper flag under the same
2070                          * tasklist_lock with adding child to the process tree
2071                          * for propagate_has_child_subreaper optimization.
2072                          */
2073                         p->signal->has_child_subreaper = p->real_parent->signal->has_child_subreaper ||
2074                                                          p->real_parent->signal->is_child_subreaper;
2075                         list_add_tail(&p->sibling, &p->real_parent->children);
2076                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
2077                         attach_pid(p, PIDTYPE_TGID);
2078                         attach_pid(p, PIDTYPE_PGID);
2079                         attach_pid(p, PIDTYPE_SID);
2080                         __this_cpu_inc(process_counts);
2081                 } else {
2082                         current->signal->nr_threads++;
2083                         atomic_inc(&current->signal->live);
2084                         refcount_inc(&current->signal->sigcnt);
2085                         task_join_group_stop(p);
2086                         list_add_tail_rcu(&p->thread_group,
2087                                           &p->group_leader->thread_group);
2088                         list_add_tail_rcu(&p->thread_node,
2089                                           &p->signal->thread_head);
2090                 }
2091                 attach_pid(p, PIDTYPE_PID);
2092                 nr_threads++;
2093         }
2094         total_forks++;
2095         hlist_del_init(&delayed.node);
2096         spin_unlock(&current->sighand->siglock);
2097         syscall_tracepoint_update(p);
2098         write_unlock_irq(&tasklist_lock);
2099
2100         proc_fork_connector(p);
2101         cgroup_post_fork(p);
2102         cgroup_threadgroup_change_end(current);
2103         perf_event_fork(p);
2104
2105         trace_task_newtask(p, clone_flags);
2106         uprobe_copy_process(p, clone_flags);
2107
2108         return p;
2109
2110 bad_fork_cancel_cgroup:
2111         spin_unlock(&current->sighand->siglock);
2112         write_unlock_irq(&tasklist_lock);
2113         cgroup_cancel_fork(p);
2114 bad_fork_free_pid:
2115         cgroup_threadgroup_change_end(current);
2116         if (pid != &init_struct_pid)
2117                 free_pid(pid);
2118 bad_fork_cleanup_thread:
2119         exit_thread(p);
2120 bad_fork_cleanup_io:
2121         if (p->io_context)
2122                 exit_io_context(p);
2123 bad_fork_cleanup_namespaces:
2124         exit_task_namespaces(p);
2125 bad_fork_cleanup_mm:
2126         if (p->mm)
2127                 mmput(p->mm);
2128 bad_fork_cleanup_signal:
2129         if (!(clone_flags & CLONE_THREAD))
2130                 free_signal_struct(p->signal);
2131 bad_fork_cleanup_sighand:
2132         __cleanup_sighand(p->sighand);
2133 bad_fork_cleanup_fs:
2134         exit_fs(p); /* blocking */
2135 bad_fork_cleanup_files:
2136         exit_files(p); /* blocking */
2137 bad_fork_cleanup_semundo:
2138         exit_sem(p);
2139 bad_fork_cleanup_security:
2140         security_task_free(p);
2141 bad_fork_cleanup_audit:
2142         audit_free(p);
2143 bad_fork_cleanup_perf:
2144         perf_event_free_task(p);
2145 bad_fork_cleanup_policy:
2146         lockdep_free_task(p);
2147 #ifdef CONFIG_NUMA
2148         mpol_put(p->mempolicy);
2149 bad_fork_cleanup_threadgroup_lock:
2150 #endif
2151         delayacct_tsk_free(p);
2152 bad_fork_cleanup_count:
2153         atomic_dec(&p->cred->user->processes);
2154         exit_creds(p);
2155 bad_fork_free:
2156         p->state = TASK_DEAD;
2157         put_task_stack(p);
2158         free_task(p);
2159 fork_out:
2160         spin_lock_irq(&current->sighand->siglock);
2161         hlist_del_init(&delayed.node);
2162         spin_unlock_irq(&current->sighand->siglock);
2163         return ERR_PTR(retval);
2164 }
2165
2166 static inline void init_idle_pids(struct task_struct *idle)
2167 {
2168         enum pid_type type;
2169
2170         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
2171                 INIT_HLIST_NODE(&idle->pid_links[type]); /* not really needed */
2172                 init_task_pid(idle, type, &init_struct_pid);
2173         }
2174 }
2175
2176 struct task_struct *fork_idle(int cpu)
2177 {
2178         struct task_struct *task;
2179         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
2180                             cpu_to_node(cpu));
2181         if (!IS_ERR(task)) {
2182                 init_idle_pids(task);
2183                 init_idle(task, cpu);
2184         }
2185
2186         return task;
2187 }
2188
2189 /*
2190  *  Ok, this is the main fork-routine.
2191  *
2192  * It copies the process, and if successful kick-starts
2193  * it and waits for it to finish using the VM if required.
2194  */
2195 long _do_fork(unsigned long clone_flags,
2196               unsigned long stack_start,
2197               unsigned long stack_size,
2198               int __user *parent_tidptr,
2199               int __user *child_tidptr,
2200               unsigned long tls)
2201 {
2202         struct completion vfork;
2203         struct pid *pid;
2204         struct task_struct *p;
2205         int trace = 0;
2206         long nr;
2207
2208         /*
2209          * Determine whether and which event to report to ptracer.  When
2210          * called from kernel_thread or CLONE_UNTRACED is explicitly
2211          * requested, no event is reported; otherwise, report if the event
2212          * for the type of forking is enabled.
2213          */
2214         if (!(clone_flags & CLONE_UNTRACED)) {
2215                 if (clone_flags & CLONE_VFORK)
2216                         trace = PTRACE_EVENT_VFORK;
2217                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
2218                         trace = PTRACE_EVENT_CLONE;
2219                 else
2220                         trace = PTRACE_EVENT_FORK;
2221
2222                 if (likely(!ptrace_event_enabled(current, trace)))
2223                         trace = 0;
2224         }
2225
2226         p = copy_process(clone_flags, stack_start, stack_size,
2227                          child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
2228         add_latent_entropy();
2229
2230         if (IS_ERR(p))
2231                 return PTR_ERR(p);
2232
2233         /*
2234          * Do this prior waking up the new thread - the thread pointer
2235          * might get invalid after that point, if the thread exits quickly.
2236          */
2237         trace_sched_process_fork(current, p);
2238
2239         pid = get_task_pid(p, PIDTYPE_PID);
2240         nr = pid_vnr(pid);
2241
2242         if (clone_flags & CLONE_PARENT_SETTID)
2243                 put_user(nr, parent_tidptr);
2244
2245         if (clone_flags & CLONE_VFORK) {
2246                 p->vfork_done = &vfork;
2247                 init_completion(&vfork);
2248                 get_task_struct(p);
2249         }
2250
2251         wake_up_new_task(p);
2252
2253         /* forking complete and child started to run, tell ptracer */
2254         if (unlikely(trace))
2255                 ptrace_event_pid(trace, pid);
2256
2257         if (clone_flags & CLONE_VFORK) {
2258                 if (!wait_for_vfork_done(p, &vfork))
2259                         ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
2260         }
2261
2262         put_pid(pid);
2263         return nr;
2264 }
2265
2266 #ifndef CONFIG_HAVE_COPY_THREAD_TLS
2267 /* For compatibility with architectures that call do_fork directly rather than
2268  * using the syscall entry points below. */
2269 long do_fork(unsigned long clone_flags,
2270               unsigned long stack_start,
2271               unsigned long stack_size,
2272               int __user *parent_tidptr,
2273               int __user *child_tidptr)
2274 {
2275         return _do_fork(clone_flags, stack_start, stack_size,
2276                         parent_tidptr, child_tidptr, 0);
2277 }
2278 #endif
2279
2280 /*
2281  * Create a kernel thread.
2282  */
2283 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
2284 {
2285         return _do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
2286                 (unsigned long)arg, NULL, NULL, 0);
2287 }
2288
2289 #ifdef __ARCH_WANT_SYS_FORK
2290 SYSCALL_DEFINE0(fork)
2291 {
2292 #ifdef CONFIG_MMU
2293         return _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0);
2294 #else
2295         /* can not support in nommu mode */
2296         return -EINVAL;
2297 #endif
2298 }
2299 #endif
2300
2301 #ifdef __ARCH_WANT_SYS_VFORK
2302 SYSCALL_DEFINE0(vfork)
2303 {
2304         return _do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
2305                         0, NULL, NULL, 0);
2306 }
2307 #endif
2308
2309 #ifdef __ARCH_WANT_SYS_CLONE
2310 #ifdef CONFIG_CLONE_BACKWARDS
2311 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
2312                  int __user *, parent_tidptr,
2313                  unsigned long, tls,
2314                  int __user *, child_tidptr)
2315 #elif defined(CONFIG_CLONE_BACKWARDS2)
2316 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
2317                  int __user *, parent_tidptr,
2318                  int __user *, child_tidptr,
2319                  unsigned long, tls)
2320 #elif defined(CONFIG_CLONE_BACKWARDS3)
2321 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
2322                 int, stack_size,
2323                 int __user *, parent_tidptr,
2324                 int __user *, child_tidptr,
2325                 unsigned long, tls)
2326 #else
2327 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
2328                  int __user *, parent_tidptr,
2329                  int __user *, child_tidptr,
2330                  unsigned long, tls)
2331 #endif
2332 {
2333         return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls);
2334 }
2335 #endif
2336
2337 void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
2338 {
2339         struct task_struct *leader, *parent, *child;
2340         int res;
2341
2342         read_lock(&tasklist_lock);
2343         leader = top = top->group_leader;
2344 down:
2345         for_each_thread(leader, parent) {
2346                 list_for_each_entry(child, &parent->children, sibling) {
2347                         res = visitor(child, data);
2348                         if (res) {
2349                                 if (res < 0)
2350                                         goto out;
2351                                 leader = child;
2352                                 goto down;
2353                         }
2354 up:
2355                         ;
2356                 }
2357         }
2358
2359         if (leader != top) {
2360                 child = leader;
2361                 parent = child->real_parent;
2362                 leader = parent->group_leader;
2363                 goto up;
2364         }
2365 out:
2366         read_unlock(&tasklist_lock);
2367 }
2368
2369 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
2370 #define ARCH_MIN_MMSTRUCT_ALIGN 0
2371 #endif
2372
2373 static void sighand_ctor(void *data)
2374 {
2375         struct sighand_struct *sighand = data;
2376
2377         spin_lock_init(&sighand->siglock);
2378         init_waitqueue_head(&sighand->signalfd_wqh);
2379 }
2380
2381 void __init proc_caches_init(void)
2382 {
2383         unsigned int mm_size;
2384
2385         sighand_cachep = kmem_cache_create("sighand_cache",
2386                         sizeof(struct sighand_struct), 0,
2387                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
2388                         SLAB_ACCOUNT, sighand_ctor);
2389         signal_cachep = kmem_cache_create("signal_cache",
2390                         sizeof(struct signal_struct), 0,
2391                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2392                         NULL);
2393         files_cachep = kmem_cache_create("files_cache",
2394                         sizeof(struct files_struct), 0,
2395                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2396                         NULL);
2397         fs_cachep = kmem_cache_create("fs_cache",
2398                         sizeof(struct fs_struct), 0,
2399                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2400                         NULL);
2401
2402         /*
2403          * The mm_cpumask is located at the end of mm_struct, and is
2404          * dynamically sized based on the maximum CPU number this system
2405          * can have, taking hotplug into account (nr_cpu_ids).
2406          */
2407         mm_size = sizeof(struct mm_struct) + cpumask_size();
2408
2409         mm_cachep = kmem_cache_create_usercopy("mm_struct",
2410                         mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
2411                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2412                         offsetof(struct mm_struct, saved_auxv),
2413                         sizeof_field(struct mm_struct, saved_auxv),
2414                         NULL);
2415         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
2416         mmap_init();
2417         nsproxy_cache_init();
2418 }
2419
2420 /*
2421  * Check constraints on flags passed to the unshare system call.
2422  */
2423 static int check_unshare_flags(unsigned long unshare_flags)
2424 {
2425         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
2426                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
2427                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
2428                                 CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWCGROUP))
2429                 return -EINVAL;
2430         /*
2431          * Not implemented, but pretend it works if there is nothing
2432          * to unshare.  Note that unsharing the address space or the
2433          * signal handlers also need to unshare the signal queues (aka
2434          * CLONE_THREAD).
2435          */
2436         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
2437                 if (!thread_group_empty(current))
2438                         return -EINVAL;
2439         }
2440         if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
2441                 if (refcount_read(&current->sighand->count) > 1)
2442                         return -EINVAL;
2443         }
2444         if (unshare_flags & CLONE_VM) {
2445                 if (!current_is_single_threaded())
2446                         return -EINVAL;
2447         }
2448
2449         return 0;
2450 }
2451
2452 /*
2453  * Unshare the filesystem structure if it is being shared
2454  */
2455 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
2456 {
2457         struct fs_struct *fs = current->fs;
2458
2459         if (!(unshare_flags & CLONE_FS) || !fs)
2460                 return 0;
2461
2462         /* don't need lock here; in the worst case we'll do useless copy */
2463         if (fs->users == 1)
2464                 return 0;
2465
2466         *new_fsp = copy_fs_struct(fs);
2467         if (!*new_fsp)
2468                 return -ENOMEM;
2469
2470         return 0;
2471 }
2472
2473 /*
2474  * Unshare file descriptor table if it is being shared
2475  */
2476 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
2477 {
2478         struct files_struct *fd = current->files;
2479         int error = 0;
2480
2481         if ((unshare_flags & CLONE_FILES) &&
2482             (fd && atomic_read(&fd->count) > 1)) {
2483                 *new_fdp = dup_fd(fd, &error);
2484                 if (!*new_fdp)
2485                         return error;
2486         }
2487
2488         return 0;
2489 }
2490
2491 /*
2492  * unshare allows a process to 'unshare' part of the process
2493  * context which was originally shared using clone.  copy_*
2494  * functions used by do_fork() cannot be used here directly
2495  * because they modify an inactive task_struct that is being
2496  * constructed. Here we are modifying the current, active,
2497  * task_struct.
2498  */
2499 int ksys_unshare(unsigned long unshare_flags)
2500 {
2501         struct fs_struct *fs, *new_fs = NULL;
2502         struct files_struct *fd, *new_fd = NULL;
2503         struct cred *new_cred = NULL;
2504         struct nsproxy *new_nsproxy = NULL;
2505         int do_sysvsem = 0;
2506         int err;
2507
2508         /*
2509          * If unsharing a user namespace must also unshare the thread group
2510          * and unshare the filesystem root and working directories.
2511          */
2512         if (unshare_flags & CLONE_NEWUSER)
2513                 unshare_flags |= CLONE_THREAD | CLONE_FS;
2514         /*
2515          * If unsharing vm, must also unshare signal handlers.
2516          */
2517         if (unshare_flags & CLONE_VM)
2518                 unshare_flags |= CLONE_SIGHAND;
2519         /*
2520          * If unsharing a signal handlers, must also unshare the signal queues.
2521          */
2522         if (unshare_flags & CLONE_SIGHAND)
2523                 unshare_flags |= CLONE_THREAD;
2524         /*
2525          * If unsharing namespace, must also unshare filesystem information.
2526          */
2527         if (unshare_flags & CLONE_NEWNS)
2528                 unshare_flags |= CLONE_FS;
2529
2530         err = check_unshare_flags(unshare_flags);
2531         if (err)
2532                 goto bad_unshare_out;
2533         /*
2534          * CLONE_NEWIPC must also detach from the undolist: after switching
2535          * to a new ipc namespace, the semaphore arrays from the old
2536          * namespace are unreachable.
2537          */
2538         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
2539                 do_sysvsem = 1;
2540         err = unshare_fs(unshare_flags, &new_fs);
2541         if (err)
2542                 goto bad_unshare_out;
2543         err = unshare_fd(unshare_flags, &new_fd);
2544         if (err)
2545                 goto bad_unshare_cleanup_fs;
2546         err = unshare_userns(unshare_flags, &new_cred);
2547         if (err)
2548                 goto bad_unshare_cleanup_fd;
2549         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
2550                                          new_cred, new_fs);
2551         if (err)
2552                 goto bad_unshare_cleanup_cred;
2553
2554         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
2555                 if (do_sysvsem) {
2556                         /*
2557                          * CLONE_SYSVSEM is equivalent to sys_exit().
2558                          */
2559                         exit_sem(current);
2560                 }
2561                 if (unshare_flags & CLONE_NEWIPC) {
2562                         /* Orphan segments in old ns (see sem above). */
2563                         exit_shm(current);
2564                         shm_init_task(current);
2565                 }
2566
2567                 if (new_nsproxy)
2568                         switch_task_namespaces(current, new_nsproxy);
2569
2570                 task_lock(current);
2571
2572                 if (new_fs) {
2573                         fs = current->fs;
2574                         spin_lock(&fs->lock);
2575                         current->fs = new_fs;
2576                         if (--fs->users)
2577                                 new_fs = NULL;
2578                         else
2579                                 new_fs = fs;
2580                         spin_unlock(&fs->lock);
2581                 }
2582
2583                 if (new_fd) {
2584                         fd = current->files;
2585                         current->files = new_fd;
2586                         new_fd = fd;
2587                 }
2588
2589                 task_unlock(current);
2590
2591                 if (new_cred) {
2592                         /* Install the new user namespace */
2593                         commit_creds(new_cred);
2594                         new_cred = NULL;
2595                 }
2596         }
2597
2598         perf_event_namespaces(current);
2599
2600 bad_unshare_cleanup_cred:
2601         if (new_cred)
2602                 put_cred(new_cred);
2603 bad_unshare_cleanup_fd:
2604         if (new_fd)
2605                 put_files_struct(new_fd);
2606
2607 bad_unshare_cleanup_fs:
2608         if (new_fs)
2609                 free_fs_struct(new_fs);
2610
2611 bad_unshare_out:
2612         return err;
2613 }
2614
2615 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
2616 {
2617         return ksys_unshare(unshare_flags);
2618 }
2619
2620 /*
2621  *      Helper to unshare the files of the current task.
2622  *      We don't want to expose copy_files internals to
2623  *      the exec layer of the kernel.
2624  */
2625
2626 int unshare_files(struct files_struct **displaced)
2627 {
2628         struct task_struct *task = current;
2629         struct files_struct *copy = NULL;
2630         int error;
2631
2632         error = unshare_fd(CLONE_FILES, &copy);
2633         if (error || !copy) {
2634                 *displaced = NULL;
2635                 return error;
2636         }
2637         *displaced = task->files;
2638         task_lock(task);
2639         task->files = copy;
2640         task_unlock(task);
2641         return 0;
2642 }
2643
2644 int sysctl_max_threads(struct ctl_table *table, int write,
2645                        void __user *buffer, size_t *lenp, loff_t *ppos)
2646 {
2647         struct ctl_table t;
2648         int ret;
2649         int threads = max_threads;
2650         int min = MIN_THREADS;
2651         int max = MAX_THREADS;
2652
2653         t = *table;
2654         t.data = &threads;
2655         t.extra1 = &min;
2656         t.extra2 = &max;
2657
2658         ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
2659         if (ret || !write)
2660                 return ret;
2661
2662         set_max_threads(threads);
2663
2664         return 0;
2665 }