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