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/init.h>
  16 #include <linux/unistd.h>
  17 #include <linux/module.h>
  18 #include <linux/vmalloc.h>
  19 #include <linux/completion.h>
  20 #include <linux/personality.h>
  21 #include <linux/mempolicy.h>
  22 #include <linux/sem.h>
  23 #include <linux/file.h>
  24 #include <linux/fdtable.h>
  25 #include <linux/iocontext.h>
  26 #include <linux/key.h>
  27 #include <linux/binfmts.h>
  28 #include <linux/mman.h>
  29 #include <linux/mmu_notifier.h>
  30 #include <linux/fs.h>
  31 #include <linux/mm.h>
  32 #include <linux/vmacache.h>
  33 #include <linux/nsproxy.h>
  34 #include <linux/capability.h>
  35 #include <linux/cpu.h>
  36 #include <linux/cgroup.h>
  37 #include <linux/security.h>
  38 #include <linux/hugetlb.h>
  39 #include <linux/seccomp.h>
  40 #include <linux/swap.h>
  41 #include <linux/syscalls.h>
  42 #include <linux/jiffies.h>
  43 #include <linux/futex.h>
  44 #include <linux/compat.h>
  45 #include <linux/kthread.h>
  46 #include <linux/task_io_accounting_ops.h>
  47 #include <linux/rcupdate.h>
  48 #include <linux/ptrace.h>
  49 #include <linux/mount.h>
  50 #include <linux/audit.h>
  51 #include <linux/memcontrol.h>
  52 #include <linux/ftrace.h>
  53 #include <linux/proc_fs.h>
  54 #include <linux/profile.h>
  55 #include <linux/rmap.h>
  56 #include <linux/ksm.h>
  57 #include <linux/acct.h>
  58 #include <linux/tsacct_kern.h>
  59 #include <linux/cn_proc.h>
  60 #include <linux/freezer.h>
  61 #include <linux/delayacct.h>
  62 #include <linux/taskstats_kern.h>
  63 #include <linux/random.h>
  64 #include <linux/tty.h>
  65 #include <linux/blkdev.h>
  66 #include <linux/fs_struct.h>
  67 #include <linux/magic.h>
  68 #include <linux/perf_event.h>
  69 #include <linux/posix-timers.h>
  70 #include <linux/user-return-notifier.h>
  71 #include <linux/oom.h>
  72 #include <linux/khugepaged.h>
  73 #include <linux/signalfd.h>
  74 #include <linux/uprobes.h>
  75 #include <linux/aio.h>
  76 #include <linux/compiler.h>
  77
  78 #include <asm/pgtable.h>
  79 #include <asm/pgalloc.h>
  80 #include <asm/uaccess.h>
  81 #include <asm/mmu_context.h>
  82 #include <asm/cacheflush.h>
  83 #include <asm/tlbflush.h>
  84
  85 #include <trace/events/sched.h>
  86
  87 #define CREATE_TRACE_POINTS
  88 #include <trace/events/task.h>
  89
  90 /*
  91  * Protected counters by write_lock_irq(&tasklist_lock)
  92  */
  93 unsigned long total_forks;      /* Handle normal Linux uptimes. */
  94 int nr_threads;                 /* The idle threads do not count.. */
  95
  96 int max_threads;                /* tunable limit on nr_threads */
  97
  98 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
  99
 100 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
 101
 102 #ifdef CONFIG_PROVE_RCU
 103 int lockdep_tasklist_lock_is_held(void)
 104 {
 105         return lockdep_is_held(&tasklist_lock);
 106 }
 107 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
 108 #endif /* #ifdef CONFIG_PROVE_RCU */
 109
 110 int nr_processes(void)
 111 {
 112         int cpu;
 113         int total = 0;
 114
 115         for_each_possible_cpu(cpu)
 116                 total += per_cpu(process_counts, cpu);
 117
 118         return total;
 119 }
 120
 121 void __weak arch_release_task_struct(struct task_struct *tsk)
 122 {
 123 }
 124
 125 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 126 static struct kmem_cache *task_struct_cachep;
 127
 128 static inline struct task_struct *alloc_task_struct_node(int node)
 129 {
 130         return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
 131 }
 132
 133 static inline void free_task_struct(struct task_struct *tsk)
 134 {
 135         kmem_cache_free(task_struct_cachep, tsk);
 136 }
 137 #endif
 138
 139 void __weak arch_release_thread_info(struct thread_info *ti)
 140 {
 141 }
 142
 143 #ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
 144
 145 /*
 146  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
 147  * kmemcache based allocator.
 148  */
 149 # if THREAD_SIZE >= PAGE_SIZE
 150 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 151                                                   int node)
 152 {
 153         struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
 154                                                   THREAD_SIZE_ORDER);
 155
 156         return page ? page_address(page) : NULL;
 157 }
 158
 159 static inline void free_thread_info(struct thread_info *ti)
 160 {
 161         free_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 162 }
 163 # else
 164 static struct kmem_cache *thread_info_cache;
 165
 166 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 167                                                   int node)
 168 {
 169         return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
 170 }
 171
 172 static void free_thread_info(struct thread_info *ti)
 173 {
 174         kmem_cache_free(thread_info_cache, ti);
 175 }
 176
 177 void thread_info_cache_init(void)
 178 {
 179         thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
 180                                               THREAD_SIZE, 0, NULL);
 181         BUG_ON(thread_info_cache == NULL);
 182 }
 183 # endif
 184 #endif
 185
 186 /* SLAB cache for signal_struct structures (tsk->signal) */
 187 static struct kmem_cache *signal_cachep;
 188
 189 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 190 struct kmem_cache *sighand_cachep;
 191
 192 /* SLAB cache for files_struct structures (tsk->files) */
 193 struct kmem_cache *files_cachep;
 194
 195 /* SLAB cache for fs_struct structures (tsk->fs) */
 196 struct kmem_cache *fs_cachep;
 197
 198 /* SLAB cache for vm_area_struct structures */
 199 struct kmem_cache *vm_area_cachep;
 200
 201 /* SLAB cache for mm_struct structures (tsk->mm) */
 202 static struct kmem_cache *mm_cachep;
 203
 204 static void account_kernel_stack(struct thread_info *ti, int account)
 205 {
 206         struct zone *zone = page_zone(virt_to_page(ti));
 207
 208         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
 209 }
 210
 211 void free_task(struct task_struct *tsk)
 212 {
 213         account_kernel_stack(tsk->stack, -1);
 214         arch_release_thread_info(tsk->stack);
 215         free_thread_info(tsk->stack);
 216         rt_mutex_debug_task_free(tsk);
 217         ftrace_graph_exit_task(tsk);
 218         put_seccomp_filter(tsk);
 219         arch_release_task_struct(tsk);
 220         free_task_struct(tsk);
 221 }
 222 EXPORT_SYMBOL(free_task);
 223
 224 static inline void free_signal_struct(struct signal_struct *sig)
 225 {
 226         taskstats_tgid_free(sig);
 227         sched_autogroup_exit(sig);
 228         kmem_cache_free(signal_cachep, sig);
 229 }
 230
 231 static inline void put_signal_struct(struct signal_struct *sig)
 232 {
 233         if (atomic_dec_and_test(&sig->sigcnt))
 234                 free_signal_struct(sig);
 235 }
 236
 237 void __put_task_struct(struct task_struct *tsk)
 238 {
 239         WARN_ON(!tsk->exit_state);
 240         WARN_ON(atomic_read(&tsk->usage));
 241         WARN_ON(tsk == current);
 242
 243         task_numa_free(tsk);
 244         security_task_free(tsk);
 245         exit_creds(tsk);
 246         delayacct_tsk_free(tsk);
 247         put_signal_struct(tsk->signal);
 248
 249         if (!profile_handoff_task(tsk))
 250                 free_task(tsk);
 251 }
 252 EXPORT_SYMBOL_GPL(__put_task_struct);
 253
 254 void __init __weak arch_task_cache_init(void) { }
 255
 256 void __init fork_init(unsigned long mempages)
 257 {
 258 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 259 #ifndef ARCH_MIN_TASKALIGN
 260 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
 261 #endif
 262         /* create a slab on which task_structs can be allocated */
 263         task_struct_cachep =
 264                 kmem_cache_create("task_struct", sizeof(struct task_struct),
 265                         ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
 266 #endif
 267
 268         /* do the arch specific task caches init */
 269         arch_task_cache_init();
 270
 271         /*
 272          * The default maximum number of threads is set to a safe
 273          * value: the thread structures can take up at most half
 274          * of memory.
 275          */
 276         max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
 277
 278         /*
 279          * we need to allow at least 20 threads to boot a system
 280          */
 281         if (max_threads < 20)
 282                 max_threads = 20;
 283
 284         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 285         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
 286         init_task.signal->rlim[RLIMIT_SIGPENDING] =
 287                 init_task.signal->rlim[RLIMIT_NPROC];
 288 }
 289
 290 int __weak arch_dup_task_struct(struct task_struct *dst,
 291                                                struct task_struct *src)
 292 {
 293         *dst = *src;
 294         return 0;
 295 }
 296
 297 static struct task_struct *dup_task_struct(struct task_struct *orig)
 298 {
 299         struct task_struct *tsk;
 300         struct thread_info *ti;
 301         unsigned long *stackend;
 302         int node = tsk_fork_get_node(orig);
 303         int err;
 304
 305         tsk = alloc_task_struct_node(node);
 306         if (!tsk)
 307                 return NULL;
 308
 309         ti = alloc_thread_info_node(tsk, node);
 310         if (!ti)
 311                 goto free_tsk;
 312
 313         err = arch_dup_task_struct(tsk, orig);
 314         if (err)
 315                 goto free_ti;
 316
 317         tsk->stack = ti;
 318 #ifdef CONFIG_SECCOMP
 319         /*
 320          * We must handle setting up seccomp filters once we're under
 321          * the sighand lock in case orig has changed between now and
 322          * then. Until then, filter must be NULL to avoid messing up
 323          * the usage counts on the error path calling free_task.
 324          */
 325         tsk->seccomp.filter = NULL;
 326 #endif
 327
 328         setup_thread_stack(tsk, orig);
 329         clear_user_return_notifier(tsk);
 330         clear_tsk_need_resched(tsk);
 331         stackend = end_of_stack(tsk);
 332         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 333
 334 #ifdef CONFIG_CC_STACKPROTECTOR
 335         tsk->stack_canary = get_random_int();
 336 #endif
 337
 338         /*
 339          * One for us, one for whoever does the "release_task()" (usually
 340          * parent)
 341          */
 342         atomic_set(&tsk->usage, 2);
 343 #ifdef CONFIG_BLK_DEV_IO_TRACE
 344         tsk->btrace_seq = 0;
 345 #endif
 346         tsk->splice_pipe = NULL;
 347         tsk->task_frag.page = NULL;
 348
 349         account_kernel_stack(ti, 1);
 350
 351         return tsk;
 352
 353 free_ti:
 354         free_thread_info(ti);
 355 free_tsk:
 356         free_task_struct(tsk);
 357         return NULL;
 358 }
 359
 360 #ifdef CONFIG_MMU
 361 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 362 {
 363         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 364         struct rb_node **rb_link, *rb_parent;
 365         int retval;
 366         unsigned long charge;
 367
 368         uprobe_start_dup_mmap();
 369         down_write(&oldmm->mmap_sem);
 370         flush_cache_dup_mm(oldmm);
 371         uprobe_dup_mmap(oldmm, mm);
 372         /*
 373          * Not linked in yet - no deadlock potential:
 374          */
 375         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 376
 377         mm->locked_vm = 0;
 378         mm->mmap = NULL;
 379         mm->vmacache_seqnum = 0;
 380         mm->map_count = 0;
 381         cpumask_clear(mm_cpumask(mm));
 382         mm->mm_rb = RB_ROOT;
 383         rb_link = &mm->mm_rb.rb_node;
 384         rb_parent = NULL;
 385         pprev = &mm->mmap;
 386         retval = ksm_fork(mm, oldmm);
 387         if (retval)
 388                 goto out;
 389         retval = khugepaged_fork(mm, oldmm);
 390         if (retval)
 391                 goto out;
 392
 393         prev = NULL;
 394         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 395                 struct file *file;
 396
 397                 if (mpnt->vm_flags & VM_DONTCOPY) {
 398                         vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
 399                                                         -vma_pages(mpnt));
 400                         continue;
 401                 }
 402                 charge = 0;
 403                 if (mpnt->vm_flags & VM_ACCOUNT) {
 404                         unsigned long len = vma_pages(mpnt);
 405
 406                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
 407                                 goto fail_nomem;
 408                         charge = len;
 409                 }
 410                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 411                 if (!tmp)
 412                         goto fail_nomem;
 413                 *tmp = *mpnt;
 414                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
 415                 retval = vma_dup_policy(mpnt, tmp);
 416                 if (retval)
 417                         goto fail_nomem_policy;
 418                 tmp->vm_mm = mm;
 419                 if (anon_vma_fork(tmp, mpnt))
 420                         goto fail_nomem_anon_vma_fork;
 421                 tmp->vm_flags &= ~VM_LOCKED;
 422                 tmp->vm_next = tmp->vm_prev = NULL;
 423                 file = tmp->vm_file;
 424                 if (file) {
 425                         struct inode *inode = file_inode(file);
 426                         struct address_space *mapping = file->f_mapping;
 427
 428                         get_file(file);
 429                         if (tmp->vm_flags & VM_DENYWRITE)
 430                                 atomic_dec(&inode->i_writecount);
 431                         mutex_lock(&mapping->i_mmap_mutex);
 432                         if (tmp->vm_flags & VM_SHARED)
 433                                 mapping->i_mmap_writable++;
 434                         flush_dcache_mmap_lock(mapping);
 435                         /* insert tmp into the share list, just after mpnt */
 436                         if (unlikely(tmp->vm_flags & VM_NONLINEAR))
 437                                 vma_nonlinear_insert(tmp,
 438                                                 &mapping->i_mmap_nonlinear);
 439                         else
 440                                 vma_interval_tree_insert_after(tmp, mpnt,
 441                                                         &mapping->i_mmap);
 442                         flush_dcache_mmap_unlock(mapping);
 443                         mutex_unlock(&mapping->i_mmap_mutex);
 444                 }
 445
 446                 /*
 447                  * Clear hugetlb-related page reserves for children. This only
 448                  * affects MAP_PRIVATE mappings. Faults generated by the child
 449                  * are not guaranteed to succeed, even if read-only
 450                  */
 451                 if (is_vm_hugetlb_page(tmp))
 452                         reset_vma_resv_huge_pages(tmp);
 453
 454                 /*
 455                  * Link in the new vma and copy the page table entries.
 456                  */
 457                 *pprev = tmp;
 458                 pprev = &tmp->vm_next;
 459                 tmp->vm_prev = prev;
 460                 prev = tmp;
 461
 462                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 463                 rb_link = &tmp->vm_rb.rb_right;
 464                 rb_parent = &tmp->vm_rb;
 465
 466                 mm->map_count++;
 467                 retval = copy_page_range(mm, oldmm, mpnt);
 468
 469                 if (tmp->vm_ops && tmp->vm_ops->open)
 470                         tmp->vm_ops->open(tmp);
 471
 472                 if (retval)
 473                         goto out;
 474         }
 475         /* a new mm has just been created */
 476         arch_dup_mmap(oldmm, mm);
 477         retval = 0;
 478 out:
 479         up_write(&mm->mmap_sem);
 480         flush_tlb_mm(oldmm);
 481         up_write(&oldmm->mmap_sem);
 482         uprobe_end_dup_mmap();
 483         return retval;
 484 fail_nomem_anon_vma_fork:
 485         mpol_put(vma_policy(tmp));
 486 fail_nomem_policy:
 487         kmem_cache_free(vm_area_cachep, tmp);
 488 fail_nomem:
 489         retval = -ENOMEM;
 490         vm_unacct_memory(charge);
 491         goto out;
 492 }
 493
 494 static inline int mm_alloc_pgd(struct mm_struct *mm)
 495 {
 496         mm->pgd = pgd_alloc(mm);
 497         if (unlikely(!mm->pgd))
 498                 return -ENOMEM;
 499         return 0;
 500 }
 501
 502 static inline void mm_free_pgd(struct mm_struct *mm)
 503 {
 504         pgd_free(mm, mm->pgd);
 505 }
 506 #else
 507 #define dup_mmap(mm, oldmm)     (0)
 508 #define mm_alloc_pgd(mm)        (0)
 509 #define mm_free_pgd(mm)
 510 #endif /* CONFIG_MMU */
 511
 512 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 513
 514 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 515 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 516
 517 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 518
 519 static int __init coredump_filter_setup(char *s)
 520 {
 521         default_dump_filter =
 522                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 523                 MMF_DUMP_FILTER_MASK;
 524         return 1;
 525 }
 526
 527 __setup("coredump_filter=", coredump_filter_setup);
 528
 529 #include <linux/init_task.h>
 530
 531 static void mm_init_aio(struct mm_struct *mm)
 532 {
 533 #ifdef CONFIG_AIO
 534         spin_lock_init(&mm->ioctx_lock);
 535         mm->ioctx_table = NULL;
 536 #endif
 537 }
 538
 539 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 540 {
 541         atomic_set(&mm->mm_users, 1);
 542         atomic_set(&mm->mm_count, 1);
 543         init_rwsem(&mm->mmap_sem);
 544         INIT_LIST_HEAD(&mm->mmlist);
 545         mm->core_state = NULL;
 546         atomic_long_set(&mm->nr_ptes, 0);
 547         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 548         spin_lock_init(&mm->page_table_lock);
 549         mm_init_aio(mm);
 550         mm_init_owner(mm, p);
 551         clear_tlb_flush_pending(mm);
 552
 553         if (current->mm) {
 554                 mm->flags = current->mm->flags & MMF_INIT_MASK;
 555                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
 556         } else {
 557                 mm->flags = default_dump_filter;
 558                 mm->def_flags = 0;
 559         }
 560
 561         if (likely(!mm_alloc_pgd(mm))) {
 562                 mmu_notifier_mm_init(mm);
 563                 return mm;
 564         }
 565
 566         free_mm(mm);
 567         return NULL;
 568 }
 569
 570 static void check_mm(struct mm_struct *mm)
 571 {
 572         int i;
 573
 574         for (i = 0; i < NR_MM_COUNTERS; i++) {
 575                 long x = atomic_long_read(&mm->rss_stat.count[i]);
 576
 577                 if (unlikely(x))
 578                         printk(KERN_ALERT "BUG: Bad rss-counter state "
 579                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
 580         }
 581
 582 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 583         VM_BUG_ON(mm->pmd_huge_pte);
 584 #endif
 585 }
 586
 587 /*
 588  * Allocate and initialize an mm_struct.
 589  */
 590 struct mm_struct *mm_alloc(void)
 591 {
 592         struct mm_struct *mm;
 593
 594         mm = allocate_mm();
 595         if (!mm)
 596                 return NULL;
 597
 598         memset(mm, 0, sizeof(*mm));
 599         mm_init_cpumask(mm);
 600         return mm_init(mm, current);
 601 }
 602
 603 /*
 604  * Called when the last reference to the mm
 605  * is dropped: either by a lazy thread or by
 606  * mmput. Free the page directory and the mm.
 607  */
 608 void __mmdrop(struct mm_struct *mm)
 609 {
 610         BUG_ON(mm == &init_mm);
 611         mm_free_pgd(mm);
 612         destroy_context(mm);
 613         mmu_notifier_mm_destroy(mm);
 614         check_mm(mm);
 615         free_mm(mm);
 616 }
 617 EXPORT_SYMBOL_GPL(__mmdrop);
 618
 619 /*
 620  * Decrement the use count and release all resources for an mm.
 621  */
 622 void mmput(struct mm_struct *mm)
 623 {
 624         might_sleep();
 625
 626         if (atomic_dec_and_test(&mm->mm_users)) {
 627                 uprobe_clear_state(mm);
 628                 exit_aio(mm);
 629                 ksm_exit(mm);
 630                 khugepaged_exit(mm); /* must run before exit_mmap */
 631                 exit_mmap(mm);
 632                 set_mm_exe_file(mm, NULL);
 633                 if (!list_empty(&mm->mmlist)) {
 634                         spin_lock(&mmlist_lock);
 635                         list_del(&mm->mmlist);
 636                         spin_unlock(&mmlist_lock);
 637                 }
 638                 if (mm->binfmt)
 639                         module_put(mm->binfmt->module);
 640                 mmdrop(mm);
 641         }
 642 }
 643 EXPORT_SYMBOL_GPL(mmput);
 644
 645 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 646 {
 647         if (new_exe_file)
 648                 get_file(new_exe_file);
 649         if (mm->exe_file)
 650                 fput(mm->exe_file);
 651         mm->exe_file = new_exe_file;
 652 }
 653
 654 struct file *get_mm_exe_file(struct mm_struct *mm)
 655 {
 656         struct file *exe_file;
 657
 658         /* We need mmap_sem to protect against races with removal of exe_file */
 659         down_read(&mm->mmap_sem);
 660         exe_file = mm->exe_file;
 661         if (exe_file)
 662                 get_file(exe_file);
 663         up_read(&mm->mmap_sem);
 664         return exe_file;
 665 }
 666
 667 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
 668 {
 669         /* It's safe to write the exe_file pointer without exe_file_lock because
 670          * this is called during fork when the task is not yet in /proc */
 671         newmm->exe_file = get_mm_exe_file(oldmm);
 672 }
 673
 674 /**
 675  * get_task_mm - acquire a reference to the task's mm
 676  *
 677  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
 678  * this kernel workthread has transiently adopted a user mm with use_mm,
 679  * to do its AIO) is not set and if so returns a reference to it, after
 680  * bumping up the use count.  User must release the mm via mmput()
 681  * after use.  Typically used by /proc and ptrace.
 682  */
 683 struct mm_struct *get_task_mm(struct task_struct *task)
 684 {
 685         struct mm_struct *mm;
 686
 687         task_lock(task);
 688         mm = task->mm;
 689         if (mm) {
 690                 if (task->flags & PF_KTHREAD)
 691                         mm = NULL;
 692                 else
 693                         atomic_inc(&mm->mm_users);
 694         }
 695         task_unlock(task);
 696         return mm;
 697 }
 698 EXPORT_SYMBOL_GPL(get_task_mm);
 699
 700 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 701 {
 702         struct mm_struct *mm;
 703         int err;
 704
 705         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
 706         if (err)
 707                 return ERR_PTR(err);
 708
 709         mm = get_task_mm(task);
 710         if (mm && mm != current->mm &&
 711                         !ptrace_may_access(task, mode)) {
 712                 mmput(mm);
 713                 mm = ERR_PTR(-EACCES);
 714         }
 715         mutex_unlock(&task->signal->cred_guard_mutex);
 716
 717         return mm;
 718 }
 719
 720 static void complete_vfork_done(struct task_struct *tsk)
 721 {
 722         struct completion *vfork;
 723
 724         task_lock(tsk);
 725         vfork = tsk->vfork_done;
 726         if (likely(vfork)) {
 727                 tsk->vfork_done = NULL;
 728                 complete(vfork);
 729         }
 730         task_unlock(tsk);
 731 }
 732
 733 static int wait_for_vfork_done(struct task_struct *child,
 734                                 struct completion *vfork)
 735 {
 736         int killed;
 737
 738         freezer_do_not_count();
 739         killed = wait_for_completion_killable(vfork);
 740         freezer_count();
 741
 742         if (killed) {
 743                 task_lock(child);
 744                 child->vfork_done = NULL;
 745                 task_unlock(child);
 746         }
 747
 748         put_task_struct(child);
 749         return killed;
 750 }
 751
 752 /* Please note the differences between mmput and mm_release.
 753  * mmput is called whenever we stop holding onto a mm_struct,
 754  * error success whatever.
 755  *
 756  * mm_release is called after a mm_struct has been removed
 757  * from the current process.
 758  *
 759  * This difference is important for error handling, when we
 760  * only half set up a mm_struct for a new process and need to restore
 761  * the old one.  Because we mmput the new mm_struct before
 762  * restoring the old one. . .
 763  * Eric Biederman 10 January 1998
 764  */
 765 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 766 {
 767         /* Get rid of any futexes when releasing the mm */
 768 #ifdef CONFIG_FUTEX
 769         if (unlikely(tsk->robust_list)) {
 770                 exit_robust_list(tsk);
 771                 tsk->robust_list = NULL;
 772         }
 773 #ifdef CONFIG_COMPAT
 774         if (unlikely(tsk->compat_robust_list)) {
 775                 compat_exit_robust_list(tsk);
 776                 tsk->compat_robust_list = NULL;
 777         }
 778 #endif
 779         if (unlikely(!list_empty(&tsk->pi_state_list)))
 780                 exit_pi_state_list(tsk);
 781 #endif
 782
 783         uprobe_free_utask(tsk);
 784
 785         /* Get rid of any cached register state */
 786         deactivate_mm(tsk, mm);
 787
 788         /*
 789          * If we're exiting normally, clear a user-space tid field if
 790          * requested.  We leave this alone when dying by signal, to leave
 791          * the value intact in a core dump, and to save the unnecessary
 792          * trouble, say, a killed vfork parent shouldn't touch this mm.
 793          * Userland only wants this done for a sys_exit.
 794          */
 795         if (tsk->clear_child_tid) {
 796                 if (!(tsk->flags & PF_SIGNALED) &&
 797                     atomic_read(&mm->mm_users) > 1) {
 798                         /*
 799                          * We don't check the error code - if userspace has
 800                          * not set up a proper pointer then tough luck.
 801                          */
 802                         put_user(0, tsk->clear_child_tid);
 803                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
 804                                         1, NULL, NULL, 0);
 805                 }
 806                 tsk->clear_child_tid = NULL;
 807         }
 808
 809         /*
 810          * All done, finally we can wake up parent and return this mm to him.
 811          * Also kthread_stop() uses this completion for synchronization.
 812          */
 813         if (tsk->vfork_done)
 814                 complete_vfork_done(tsk);
 815 }
 816
 817 /*
 818  * Allocate a new mm structure and copy contents from the
 819  * mm structure of the passed in task structure.
 820  */
 821 static struct mm_struct *dup_mm(struct task_struct *tsk)
 822 {
 823         struct mm_struct *mm, *oldmm = current->mm;
 824         int err;
 825
 826         mm = allocate_mm();
 827         if (!mm)
 828                 goto fail_nomem;
 829
 830         memcpy(mm, oldmm, sizeof(*mm));
 831         mm_init_cpumask(mm);
 832
 833 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 834         mm->pmd_huge_pte = NULL;
 835 #endif
 836         if (!mm_init(mm, tsk))
 837                 goto fail_nomem;
 838
 839         if (init_new_context(tsk, mm))
 840                 goto fail_nocontext;
 841
 842         dup_mm_exe_file(oldmm, mm);
 843
 844         err = dup_mmap(mm, oldmm);
 845         if (err)
 846                 goto free_pt;
 847
 848         mm->hiwater_rss = get_mm_rss(mm);
 849         mm->hiwater_vm = mm->total_vm;
 850
 851         if (mm->binfmt && !try_module_get(mm->binfmt->module))
 852                 goto free_pt;
 853
 854         return mm;
 855
 856 free_pt:
 857         /* don't put binfmt in mmput, we haven't got module yet */
 858         mm->binfmt = NULL;
 859         mmput(mm);
 860
 861 fail_nomem:
 862         return NULL;
 863
 864 fail_nocontext:
 865         /*
 866          * If init_new_context() failed, we cannot use mmput() to free the mm
 867          * because it calls destroy_context()
 868          */
 869         mm_free_pgd(mm);
 870         free_mm(mm);
 871         return NULL;
 872 }
 873
 874 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 875 {
 876         struct mm_struct *mm, *oldmm;
 877         int retval;
 878
 879         tsk->min_flt = tsk->maj_flt = 0;
 880         tsk->nvcsw = tsk->nivcsw = 0;
 881 #ifdef CONFIG_DETECT_HUNG_TASK
 882         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 883 #endif
 884
 885         tsk->mm = NULL;
 886         tsk->active_mm = NULL;
 887
 888         /*
 889          * Are we cloning a kernel thread?
 890          *
 891          * We need to steal a active VM for that..
 892          */
 893         oldmm = current->mm;
 894         if (!oldmm)
 895                 return 0;
 896
 897         /* initialize the new vmacache entries */
 898         vmacache_flush(tsk);
 899
 900         if (clone_flags & CLONE_VM) {
 901                 atomic_inc(&oldmm->mm_users);
 902                 mm = oldmm;
 903                 goto good_mm;
 904         }
 905
 906         retval = -ENOMEM;
 907         mm = dup_mm(tsk);
 908         if (!mm)
 909                 goto fail_nomem;
 910
 911 good_mm:
 912         tsk->mm = mm;
 913         tsk->active_mm = mm;
 914         return 0;
 915
 916 fail_nomem:
 917         return retval;
 918 }
 919
 920 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 921 {
 922         struct fs_struct *fs = current->fs;
 923         if (clone_flags & CLONE_FS) {
 924                 /* tsk->fs is already what we want */
 925                 spin_lock(&fs->lock);
 926                 if (fs->in_exec) {
 927                         spin_unlock(&fs->lock);
 928                         return -EAGAIN;
 929                 }
 930                 fs->users++;
 931                 spin_unlock(&fs->lock);
 932                 return 0;
 933         }
 934         tsk->fs = copy_fs_struct(fs);
 935         if (!tsk->fs)
 936                 return -ENOMEM;
 937         return 0;
 938 }
 939
 940 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
 941 {
 942         struct files_struct *oldf, *newf;
 943         int error = 0;
 944
 945         /*
 946          * A background process may not have any files ...
 947          */
 948         oldf = current->files;
 949         if (!oldf)
 950                 goto out;
 951
 952         if (clone_flags & CLONE_FILES) {
 953                 atomic_inc(&oldf->count);
 954                 goto out;
 955         }
 956
 957         newf = dup_fd(oldf, &error);
 958         if (!newf)
 959                 goto out;
 960
 961         tsk->files = newf;
 962         error = 0;
 963 out:
 964         return error;
 965 }
 966
 967 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 968 {
 969 #ifdef CONFIG_BLOCK
 970         struct io_context *ioc = current->io_context;
 971         struct io_context *new_ioc;
 972
 973         if (!ioc)
 974                 return 0;
 975         /*
 976          * Share io context with parent, if CLONE_IO is set
 977          */
 978         if (clone_flags & CLONE_IO) {
 979                 ioc_task_link(ioc);
 980                 tsk->io_context = ioc;
 981         } else if (ioprio_valid(ioc->ioprio)) {
 982                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
 983                 if (unlikely(!new_ioc))
 984                         return -ENOMEM;
 985
 986                 new_ioc->ioprio = ioc->ioprio;
 987                 put_io_context(new_ioc);
 988         }
 989 #endif
 990         return 0;
 991 }
 992
 993 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 994 {
 995         struct sighand_struct *sig;
 996
 997         if (clone_flags & CLONE_SIGHAND) {
 998                 atomic_inc(&current->sighand->count);
 999                 return 0;
1000         }
1001         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1002         rcu_assign_pointer(tsk->sighand, sig);
1003         if (!sig)
1004                 return -ENOMEM;
1005         atomic_set(&sig->count, 1);
1006         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1007         return 0;
1008 }
1009
1010 void __cleanup_sighand(struct sighand_struct *sighand)
1011 {
1012         if (atomic_dec_and_test(&sighand->count)) {
1013                 signalfd_cleanup(sighand);
1014                 kmem_cache_free(sighand_cachep, sighand);
1015         }
1016 }
1017
1018
1019 /*
1020  * Initialize POSIX timer handling for a thread group.
1021  */
1022 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1023 {
1024         unsigned long cpu_limit;
1025
1026         /* Thread group counters. */
1027         thread_group_cputime_init(sig);
1028
1029         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1030         if (cpu_limit != RLIM_INFINITY) {
1031                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1032                 sig->cputimer.running = 1;
1033         }
1034
1035         /* The timer lists. */
1036         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1037         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1038         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1039 }
1040
1041 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1042 {
1043         struct signal_struct *sig;
1044
1045         if (clone_flags & CLONE_THREAD)
1046                 return 0;
1047
1048         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1049         tsk->signal = sig;
1050         if (!sig)
1051                 return -ENOMEM;
1052
1053         sig->nr_threads = 1;
1054         atomic_set(&sig->live, 1);
1055         atomic_set(&sig->sigcnt, 1);
1056
1057         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1058         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1059         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1060
1061         init_waitqueue_head(&sig->wait_chldexit);
1062         sig->curr_target = tsk;
1063         init_sigpending(&sig->shared_pending);
1064         INIT_LIST_HEAD(&sig->posix_timers);
1065
1066         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1067         sig->real_timer.function = it_real_fn;
1068
1069         task_lock(current->group_leader);
1070         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1071         task_unlock(current->group_leader);
1072
1073         posix_cpu_timers_init_group(sig);
1074
1075         tty_audit_fork(sig);
1076         sched_autogroup_fork(sig);
1077
1078 #ifdef CONFIG_CGROUPS
1079         init_rwsem(&sig->group_rwsem);
1080 #endif
1081
1082         sig->oom_score_adj = current->signal->oom_score_adj;
1083         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1084
1085         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1086                                    current->signal->is_child_subreaper;
1087
1088         mutex_init(&sig->cred_guard_mutex);
1089
1090         return 0;
1091 }
1092
1093 static void copy_seccomp(struct task_struct *p)
1094 {
1095 #ifdef CONFIG_SECCOMP
1096         /*
1097          * Must be called with sighand->lock held, which is common to
1098          * all threads in the group. Holding cred_guard_mutex is not
1099          * needed because this new task is not yet running and cannot
1100          * be racing exec.
1101          */
1102         BUG_ON(!spin_is_locked(&current->sighand->siglock));
1103
1104         /* Ref-count the new filter user, and assign it. */
1105         get_seccomp_filter(current);
1106         p->seccomp = current->seccomp;
1107
1108         /*
1109          * Explicitly enable no_new_privs here in case it got set
1110          * between the task_struct being duplicated and holding the
1111          * sighand lock. The seccomp state and nnp must be in sync.
1112          */
1113         if (task_no_new_privs(current))
1114                 task_set_no_new_privs(p);
1115
1116         /*
1117          * If the parent gained a seccomp mode after copying thread
1118          * flags and between before we held the sighand lock, we have
1119          * to manually enable the seccomp thread flag here.
1120          */
1121         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1122                 set_tsk_thread_flag(p, TIF_SECCOMP);
1123 #endif
1124 }
1125
1126 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1127 {
1128         current->clear_child_tid = tidptr;
1129
1130         return task_pid_vnr(current);
1131 }
1132
1133 static void rt_mutex_init_task(struct task_struct *p)
1134 {
1135         raw_spin_lock_init(&p->pi_lock);
1136 #ifdef CONFIG_RT_MUTEXES
1137         p->pi_waiters = RB_ROOT;
1138         p->pi_waiters_leftmost = NULL;
1139         p->pi_blocked_on = NULL;
1140 #endif
1141 }
1142
1143 #ifdef CONFIG_MEMCG
1144 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1145 {
1146         mm->owner = p;
1147 }
1148 #endif /* CONFIG_MEMCG */
1149
1150 /*
1151  * Initialize POSIX timer handling for a single task.
1152  */
1153 static void posix_cpu_timers_init(struct task_struct *tsk)
1154 {
1155         tsk->cputime_expires.prof_exp = 0;
1156         tsk->cputime_expires.virt_exp = 0;
1157         tsk->cputime_expires.sched_exp = 0;
1158         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1159         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1160         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1161 }
1162
1163 static inline void
1164 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1165 {
1166          task->pids[type].pid = pid;
1167 }
1168
1169 /*
1170  * This creates a new process as a copy of the old one,
1171  * but does not actually start it yet.
1172  *
1173  * It copies the registers, and all the appropriate
1174  * parts of the process environment (as per the clone
1175  * flags). The actual kick-off is left to the caller.
1176  */
1177 static struct task_struct *copy_process(unsigned long clone_flags,
1178                                         unsigned long stack_start,
1179                                         unsigned long stack_size,
1180                                         int __user *child_tidptr,
1181                                         struct pid *pid,
1182                                         int trace)
1183 {
1184         int retval;
1185         struct task_struct *p;
1186
1187         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1188                 return ERR_PTR(-EINVAL);
1189
1190         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1191                 return ERR_PTR(-EINVAL);
1192
1193         /*
1194          * Thread groups must share signals as well, and detached threads
1195          * can only be started up within the thread group.
1196          */
1197         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1198                 return ERR_PTR(-EINVAL);
1199
1200         /*
1201          * Shared signal handlers imply shared VM. By way of the above,
1202          * thread groups also imply shared VM. Blocking this case allows
1203          * for various simplifications in other code.
1204          */
1205         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1206                 return ERR_PTR(-EINVAL);
1207
1208         /*
1209          * Siblings of global init remain as zombies on exit since they are
1210          * not reaped by their parent (swapper). To solve this and to avoid
1211          * multi-rooted process trees, prevent global and container-inits
1212          * from creating siblings.
1213          */
1214         if ((clone_flags & CLONE_PARENT) &&
1215                                 current->signal->flags & SIGNAL_UNKILLABLE)
1216                 return ERR_PTR(-EINVAL);
1217
1218         /*
1219          * If the new process will be in a different pid or user namespace
1220          * do not allow it to share a thread group or signal handlers or
1221          * parent with the forking task.
1222          */
1223         if (clone_flags & CLONE_SIGHAND) {
1224                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1225                     (task_active_pid_ns(current) !=
1226                                 current->nsproxy->pid_ns_for_children))
1227                         return ERR_PTR(-EINVAL);
1228         }
1229
1230         retval = security_task_create(clone_flags);
1231         if (retval)
1232                 goto fork_out;
1233
1234         retval = -ENOMEM;
1235         p = dup_task_struct(current);
1236         if (!p)
1237                 goto fork_out;
1238
1239         ftrace_graph_init_task(p);
1240
1241         rt_mutex_init_task(p);
1242
1243 #ifdef CONFIG_PROVE_LOCKING
1244         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1245         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1246 #endif
1247         retval = -EAGAIN;
1248         if (atomic_read(&p->real_cred->user->processes) >=
1249                         task_rlimit(p, RLIMIT_NPROC)) {
1250                 if (p->real_cred->user != INIT_USER &&
1251                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1252                         goto bad_fork_free;
1253         }
1254         current->flags &= ~PF_NPROC_EXCEEDED;
1255
1256         retval = copy_creds(p, clone_flags);
1257         if (retval < 0)
1258                 goto bad_fork_free;
1259
1260         /*
1261          * If multiple threads are within copy_process(), then this check
1262          * triggers too late. This doesn't hurt, the check is only there
1263          * to stop root fork bombs.
1264          */
1265         retval = -EAGAIN;
1266         if (nr_threads >= max_threads)
1267                 goto bad_fork_cleanup_count;
1268
1269         if (!try_module_get(task_thread_info(p)->exec_domain->module))
1270                 goto bad_fork_cleanup_count;
1271
1272         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1273         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1274         p->flags |= PF_FORKNOEXEC;
1275         INIT_LIST_HEAD(&p->children);
1276         INIT_LIST_HEAD(&p->sibling);
1277         rcu_copy_process(p);
1278         p->vfork_done = NULL;
1279         spin_lock_init(&p->alloc_lock);
1280
1281         init_sigpending(&p->pending);
1282
1283         p->utime = p->stime = p->gtime = 0;
1284         p->utimescaled = p->stimescaled = 0;
1285 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1286         p->prev_cputime.utime = p->prev_cputime.stime = 0;
1287 #endif
1288 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1289         seqlock_init(&p->vtime_seqlock);
1290         p->vtime_snap = 0;
1291         p->vtime_snap_whence = VTIME_SLEEPING;
1292 #endif
1293
1294 #if defined(SPLIT_RSS_COUNTING)
1295         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1296 #endif
1297
1298         p->default_timer_slack_ns = current->timer_slack_ns;
1299
1300         task_io_accounting_init(&p->ioac);
1301         acct_clear_integrals(p);
1302
1303         posix_cpu_timers_init(p);
1304
1305         p->start_time = ktime_get_ns();
1306         p->real_start_time = ktime_get_boot_ns();
1307         p->io_context = NULL;
1308         p->audit_context = NULL;
1309         if (clone_flags & CLONE_THREAD)
1310                 threadgroup_change_begin(current);
1311         cgroup_fork(p);
1312 #ifdef CONFIG_NUMA
1313         p->mempolicy = mpol_dup(p->mempolicy);
1314         if (IS_ERR(p->mempolicy)) {
1315                 retval = PTR_ERR(p->mempolicy);
1316                 p->mempolicy = NULL;
1317                 goto bad_fork_cleanup_threadgroup_lock;
1318         }
1319 #endif
1320 #ifdef CONFIG_CPUSETS
1321         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1322         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1323         seqcount_init(&p->mems_allowed_seq);
1324 #endif
1325 #ifdef CONFIG_TRACE_IRQFLAGS
1326         p->irq_events = 0;
1327         p->hardirqs_enabled = 0;
1328         p->hardirq_enable_ip = 0;
1329         p->hardirq_enable_event = 0;
1330         p->hardirq_disable_ip = _THIS_IP_;
1331         p->hardirq_disable_event = 0;
1332         p->softirqs_enabled = 1;
1333         p->softirq_enable_ip = _THIS_IP_;
1334         p->softirq_enable_event = 0;
1335         p->softirq_disable_ip = 0;
1336         p->softirq_disable_event = 0;
1337         p->hardirq_context = 0;
1338         p->softirq_context = 0;
1339 #endif
1340 #ifdef CONFIG_LOCKDEP
1341         p->lockdep_depth = 0; /* no locks held yet */
1342         p->curr_chain_key = 0;
1343         p->lockdep_recursion = 0;
1344 #endif
1345
1346 #ifdef CONFIG_DEBUG_MUTEXES
1347         p->blocked_on = NULL; /* not blocked yet */
1348 #endif
1349 #ifdef CONFIG_MEMCG
1350         p->memcg_batch.do_batch = 0;
1351         p->memcg_batch.memcg = NULL;
1352 #endif
1353 #ifdef CONFIG_BCACHE
1354         p->sequential_io        = 0;
1355         p->sequential_io_avg    = 0;
1356 #endif
1357
1358         /* Perform scheduler related setup. Assign this task to a CPU. */
1359         retval = sched_fork(clone_flags, p);
1360         if (retval)
1361                 goto bad_fork_cleanup_policy;
1362
1363         retval = perf_event_init_task(p);
1364         if (retval)
1365                 goto bad_fork_cleanup_policy;
1366         retval = audit_alloc(p);
1367         if (retval)
1368                 goto bad_fork_cleanup_policy;
1369         /* copy all the process information */
1370         retval = copy_semundo(clone_flags, p);
1371         if (retval)
1372                 goto bad_fork_cleanup_audit;
1373         retval = copy_files(clone_flags, p);
1374         if (retval)
1375                 goto bad_fork_cleanup_semundo;
1376         retval = copy_fs(clone_flags, p);
1377         if (retval)
1378                 goto bad_fork_cleanup_files;
1379         retval = copy_sighand(clone_flags, p);
1380         if (retval)
1381                 goto bad_fork_cleanup_fs;
1382         retval = copy_signal(clone_flags, p);
1383         if (retval)
1384                 goto bad_fork_cleanup_sighand;
1385         retval = copy_mm(clone_flags, p);
1386         if (retval)
1387                 goto bad_fork_cleanup_signal;
1388         retval = copy_namespaces(clone_flags, p);
1389         if (retval)
1390                 goto bad_fork_cleanup_mm;
1391         retval = copy_io(clone_flags, p);
1392         if (retval)
1393                 goto bad_fork_cleanup_namespaces;
1394         retval = copy_thread(clone_flags, stack_start, stack_size, p);
1395         if (retval)
1396                 goto bad_fork_cleanup_io;
1397
1398         if (pid != &init_struct_pid) {
1399                 retval = -ENOMEM;
1400                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1401                 if (!pid)
1402                         goto bad_fork_cleanup_io;
1403         }
1404
1405         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1406         /*
1407          * Clear TID on mm_release()?
1408          */
1409         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1410 #ifdef CONFIG_BLOCK
1411         p->plug = NULL;
1412 #endif
1413 #ifdef CONFIG_FUTEX
1414         p->robust_list = NULL;
1415 #ifdef CONFIG_COMPAT
1416         p->compat_robust_list = NULL;
1417 #endif
1418         INIT_LIST_HEAD(&p->pi_state_list);
1419         p->pi_state_cache = NULL;
1420 #endif
1421         /*
1422          * sigaltstack should be cleared when sharing the same VM
1423          */
1424         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1425                 p->sas_ss_sp = p->sas_ss_size = 0;
1426
1427         /*
1428          * Syscall tracing and stepping should be turned off in the
1429          * child regardless of CLONE_PTRACE.
1430          */
1431         user_disable_single_step(p);
1432         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1433 #ifdef TIF_SYSCALL_EMU
1434         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1435 #endif
1436         clear_all_latency_tracing(p);
1437
1438         /* ok, now we should be set up.. */
1439         p->pid = pid_nr(pid);
1440         if (clone_flags & CLONE_THREAD) {
1441                 p->exit_signal = -1;
1442                 p->group_leader = current->group_leader;
1443                 p->tgid = current->tgid;
1444         } else {
1445                 if (clone_flags & CLONE_PARENT)
1446                         p->exit_signal = current->group_leader->exit_signal;
1447                 else
1448                         p->exit_signal = (clone_flags & CSIGNAL);
1449                 p->group_leader = p;
1450                 p->tgid = p->pid;
1451         }
1452
1453         p->nr_dirtied = 0;
1454         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1455         p->dirty_paused_when = 0;
1456
1457         p->pdeath_signal = 0;
1458         INIT_LIST_HEAD(&p->thread_group);
1459         p->task_works = NULL;
1460
1461         /*
1462          * Make it visible to the rest of the system, but dont wake it up yet.
1463          * Need tasklist lock for parent etc handling!
1464          */
1465         write_lock_irq(&tasklist_lock);
1466
1467         /* CLONE_PARENT re-uses the old parent */
1468         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1469                 p->real_parent = current->real_parent;
1470                 p->parent_exec_id = current->parent_exec_id;
1471         } else {
1472                 p->real_parent = current;
1473                 p->parent_exec_id = current->self_exec_id;
1474         }
1475
1476         spin_lock(&current->sighand->siglock);
1477
1478         /*
1479          * Copy seccomp details explicitly here, in case they were changed
1480          * before holding sighand lock.
1481          */
1482         copy_seccomp(p);
1483
1484         /*
1485          * Process group and session signals need to be delivered to just the
1486          * parent before the fork or both the parent and the child after the
1487          * fork. Restart if a signal comes in before we add the new process to
1488          * it's process group.
1489          * A fatal signal pending means that current will exit, so the new
1490          * thread can't slip out of an OOM kill (or normal SIGKILL).
1491         */
1492         recalc_sigpending();
1493         if (signal_pending(current)) {
1494                 spin_unlock(&current->sighand->siglock);
1495                 write_unlock_irq(&tasklist_lock);
1496                 retval = -ERESTARTNOINTR;
1497                 goto bad_fork_free_pid;
1498         }
1499
1500         if (likely(p->pid)) {
1501                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1502
1503                 init_task_pid(p, PIDTYPE_PID, pid);
1504                 if (thread_group_leader(p)) {
1505                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1506                         init_task_pid(p, PIDTYPE_SID, task_session(current));
1507
1508                         if (is_child_reaper(pid)) {
1509                                 ns_of_pid(pid)->child_reaper = p;
1510                                 p->signal->flags |= SIGNAL_UNKILLABLE;
1511                         }
1512
1513                         p->signal->leader_pid = pid;
1514                         p->signal->tty = tty_kref_get(current->signal->tty);
1515                         list_add_tail(&p->sibling, &p->real_parent->children);
1516                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1517                         attach_pid(p, PIDTYPE_PGID);
1518                         attach_pid(p, PIDTYPE_SID);
1519                         __this_cpu_inc(process_counts);
1520                 } else {
1521                         current->signal->nr_threads++;
1522                         atomic_inc(&current->signal->live);
1523                         atomic_inc(&current->signal->sigcnt);
1524                         list_add_tail_rcu(&p->thread_group,
1525                                           &p->group_leader->thread_group);
1526                         list_add_tail_rcu(&p->thread_node,
1527                                           &p->signal->thread_head);
1528                 }
1529                 attach_pid(p, PIDTYPE_PID);
1530                 nr_threads++;
1531         }
1532
1533         total_forks++;
1534         spin_unlock(&current->sighand->siglock);
1535         syscall_tracepoint_update(p);
1536         write_unlock_irq(&tasklist_lock);
1537
1538         proc_fork_connector(p);
1539         cgroup_post_fork(p);
1540         if (clone_flags & CLONE_THREAD)
1541                 threadgroup_change_end(current);
1542         perf_event_fork(p);
1543
1544         trace_task_newtask(p, clone_flags);
1545         uprobe_copy_process(p, clone_flags);
1546
1547         return p;
1548
1549 bad_fork_free_pid:
1550         if (pid != &init_struct_pid)
1551                 free_pid(pid);
1552 bad_fork_cleanup_io:
1553         if (p->io_context)
1554                 exit_io_context(p);
1555 bad_fork_cleanup_namespaces:
1556         exit_task_namespaces(p);
1557 bad_fork_cleanup_mm:
1558         if (p->mm)
1559                 mmput(p->mm);
1560 bad_fork_cleanup_signal:
1561         if (!(clone_flags & CLONE_THREAD))
1562                 free_signal_struct(p->signal);
1563 bad_fork_cleanup_sighand:
1564         __cleanup_sighand(p->sighand);
1565 bad_fork_cleanup_fs:
1566         exit_fs(p); /* blocking */
1567 bad_fork_cleanup_files:
1568         exit_files(p); /* blocking */
1569 bad_fork_cleanup_semundo:
1570         exit_sem(p);
1571 bad_fork_cleanup_audit:
1572         audit_free(p);
1573 bad_fork_cleanup_policy:
1574         perf_event_free_task(p);
1575 #ifdef CONFIG_NUMA
1576         mpol_put(p->mempolicy);
1577 bad_fork_cleanup_threadgroup_lock:
1578 #endif
1579         if (clone_flags & CLONE_THREAD)
1580                 threadgroup_change_end(current);
1581         delayacct_tsk_free(p);
1582         module_put(task_thread_info(p)->exec_domain->module);
1583 bad_fork_cleanup_count:
1584         atomic_dec(&p->cred->user->processes);
1585         exit_creds(p);
1586 bad_fork_free:
1587         free_task(p);
1588 fork_out:
1589         return ERR_PTR(retval);
1590 }
1591
1592 static inline void init_idle_pids(struct pid_link *links)
1593 {
1594         enum pid_type type;
1595
1596         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1597                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1598                 links[type].pid = &init_struct_pid;
1599         }
1600 }
1601
1602 struct task_struct *fork_idle(int cpu)
1603 {
1604         struct task_struct *task;
1605         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1606         if (!IS_ERR(task)) {
1607                 init_idle_pids(task->pids);
1608                 init_idle(task, cpu);
1609         }
1610
1611         return task;
1612 }
1613
1614 /*
1615  *  Ok, this is the main fork-routine.
1616  *
1617  * It copies the process, and if successful kick-starts
1618  * it and waits for it to finish using the VM if required.
1619  */
1620 long do_fork(unsigned long clone_flags,
1621               unsigned long stack_start,
1622               unsigned long stack_size,
1623               int __user *parent_tidptr,
1624               int __user *child_tidptr)
1625 {
1626         struct task_struct *p;
1627         int trace = 0;
1628         long nr;
1629
1630         /*
1631          * Determine whether and which event to report to ptracer.  When
1632          * called from kernel_thread or CLONE_UNTRACED is explicitly
1633          * requested, no event is reported; otherwise, report if the event
1634          * for the type of forking is enabled.
1635          */
1636         if (!(clone_flags & CLONE_UNTRACED)) {
1637                 if (clone_flags & CLONE_VFORK)
1638                         trace = PTRACE_EVENT_VFORK;
1639                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1640                         trace = PTRACE_EVENT_CLONE;
1641                 else
1642                         trace = PTRACE_EVENT_FORK;
1643
1644                 if (likely(!ptrace_event_enabled(current, trace)))
1645                         trace = 0;
1646         }
1647
1648         p = copy_process(clone_flags, stack_start, stack_size,
1649                          child_tidptr, NULL, trace);
1650         /*
1651          * Do this prior waking up the new thread - the thread pointer
1652          * might get invalid after that point, if the thread exits quickly.
1653          */
1654         if (!IS_ERR(p)) {
1655                 struct completion vfork;
1656                 struct pid *pid;
1657
1658                 trace_sched_process_fork(current, p);
1659
1660                 pid = get_task_pid(p, PIDTYPE_PID);
1661                 nr = pid_vnr(pid);
1662
1663                 if (clone_flags & CLONE_PARENT_SETTID)
1664                         put_user(nr, parent_tidptr);
1665
1666                 if (clone_flags & CLONE_VFORK) {
1667                         p->vfork_done = &vfork;
1668                         init_completion(&vfork);
1669                         get_task_struct(p);
1670                 }
1671
1672                 wake_up_new_task(p);
1673
1674                 /* forking complete and child started to run, tell ptracer */
1675                 if (unlikely(trace))
1676                         ptrace_event_pid(trace, pid);
1677
1678                 if (clone_flags & CLONE_VFORK) {
1679                         if (!wait_for_vfork_done(p, &vfork))
1680                                 ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
1681                 }
1682
1683                 put_pid(pid);
1684         } else {
1685                 nr = PTR_ERR(p);
1686         }
1687         return nr;
1688 }
1689
1690 /*
1691  * Create a kernel thread.
1692  */
1693 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1694 {
1695         return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1696                 (unsigned long)arg, NULL, NULL);
1697 }
1698
1699 #ifdef __ARCH_WANT_SYS_FORK
1700 SYSCALL_DEFINE0(fork)
1701 {
1702 #ifdef CONFIG_MMU
1703         return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1704 #else
1705         /* can not support in nommu mode */
1706         return -EINVAL;
1707 #endif
1708 }
1709 #endif
1710
1711 #ifdef __ARCH_WANT_SYS_VFORK
1712 SYSCALL_DEFINE0(vfork)
1713 {
1714         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1715                         0, NULL, NULL);
1716 }
1717 #endif
1718
1719 #ifdef __ARCH_WANT_SYS_CLONE
1720 #ifdef CONFIG_CLONE_BACKWARDS
1721 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1722                  int __user *, parent_tidptr,
1723                  int, tls_val,
1724                  int __user *, child_tidptr)
1725 #elif defined(CONFIG_CLONE_BACKWARDS2)
1726 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1727                  int __user *, parent_tidptr,
1728                  int __user *, child_tidptr,
1729                  int, tls_val)
1730 #elif defined(CONFIG_CLONE_BACKWARDS3)
1731 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1732                 int, stack_size,
1733                 int __user *, parent_tidptr,
1734                 int __user *, child_tidptr,
1735                 int, tls_val)
1736 #else
1737 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1738                  int __user *, parent_tidptr,
1739                  int __user *, child_tidptr,
1740                  int, tls_val)
1741 #endif
1742 {
1743         return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1744 }
1745 #endif
1746
1747 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1748 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1749 #endif
1750
1751 static void sighand_ctor(void *data)
1752 {
1753         struct sighand_struct *sighand = data;
1754
1755         spin_lock_init(&sighand->siglock);
1756         init_waitqueue_head(&sighand->signalfd_wqh);
1757 }
1758
1759 void __init proc_caches_init(void)
1760 {
1761         sighand_cachep = kmem_cache_create("sighand_cache",
1762                         sizeof(struct sighand_struct), 0,
1763                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1764                         SLAB_NOTRACK, sighand_ctor);
1765         signal_cachep = kmem_cache_create("signal_cache",
1766                         sizeof(struct signal_struct), 0,
1767                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1768         files_cachep = kmem_cache_create("files_cache",
1769                         sizeof(struct files_struct), 0,
1770                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1771         fs_cachep = kmem_cache_create("fs_cache",
1772                         sizeof(struct fs_struct), 0,
1773                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1774         /*
1775          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1776          * whole struct cpumask for the OFFSTACK case. We could change
1777          * this to *only* allocate as much of it as required by the
1778          * maximum number of CPU's we can ever have.  The cpumask_allocation
1779          * is at the end of the structure, exactly for that reason.
1780          */
1781         mm_cachep = kmem_cache_create("mm_struct",
1782                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1783                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1784         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1785         mmap_init();
1786         nsproxy_cache_init();
1787 }
1788
1789 /*
1790  * Check constraints on flags passed to the unshare system call.
1791  */
1792 static int check_unshare_flags(unsigned long unshare_flags)
1793 {
1794         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1795                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1796                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1797                                 CLONE_NEWUSER|CLONE_NEWPID))
1798                 return -EINVAL;
1799         /*
1800          * Not implemented, but pretend it works if there is nothing to
1801          * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1802          * needs to unshare vm.
1803          */
1804         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1805                 /* FIXME: get_task_mm() increments ->mm_users */
1806                 if (atomic_read(&current->mm->mm_users) > 1)
1807                         return -EINVAL;
1808         }
1809
1810         return 0;
1811 }
1812
1813 /*
1814  * Unshare the filesystem structure if it is being shared
1815  */
1816 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1817 {
1818         struct fs_struct *fs = current->fs;
1819
1820         if (!(unshare_flags & CLONE_FS) || !fs)
1821                 return 0;
1822
1823         /* don't need lock here; in the worst case we'll do useless copy */
1824         if (fs->users == 1)
1825                 return 0;
1826
1827         *new_fsp = copy_fs_struct(fs);
1828         if (!*new_fsp)
1829                 return -ENOMEM;
1830
1831         return 0;
1832 }
1833
1834 /*
1835  * Unshare file descriptor table if it is being shared
1836  */
1837 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1838 {
1839         struct files_struct *fd = current->files;
1840         int error = 0;
1841
1842         if ((unshare_flags & CLONE_FILES) &&
1843             (fd && atomic_read(&fd->count) > 1)) {
1844                 *new_fdp = dup_fd(fd, &error);
1845                 if (!*new_fdp)
1846                         return error;
1847         }
1848
1849         return 0;
1850 }
1851
1852 /*
1853  * unshare allows a process to 'unshare' part of the process
1854  * context which was originally shared using clone.  copy_*
1855  * functions used by do_fork() cannot be used here directly
1856  * because they modify an inactive task_struct that is being
1857  * constructed. Here we are modifying the current, active,
1858  * task_struct.
1859  */
1860 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1861 {
1862         struct fs_struct *fs, *new_fs = NULL;
1863         struct files_struct *fd, *new_fd = NULL;
1864         struct cred *new_cred = NULL;
1865         struct nsproxy *new_nsproxy = NULL;
1866         int do_sysvsem = 0;
1867         int err;
1868
1869         /*
1870          * If unsharing a user namespace must also unshare the thread.
1871          */
1872         if (unshare_flags & CLONE_NEWUSER)
1873                 unshare_flags |= CLONE_THREAD | CLONE_FS;
1874         /*
1875          * If unsharing a thread from a thread group, must also unshare vm.
1876          */
1877         if (unshare_flags & CLONE_THREAD)
1878                 unshare_flags |= CLONE_VM;
1879         /*
1880          * If unsharing vm, must also unshare signal handlers.
1881          */
1882         if (unshare_flags & CLONE_VM)
1883                 unshare_flags |= CLONE_SIGHAND;
1884         /*
1885          * If unsharing namespace, must also unshare filesystem information.
1886          */
1887         if (unshare_flags & CLONE_NEWNS)
1888                 unshare_flags |= CLONE_FS;
1889
1890         err = check_unshare_flags(unshare_flags);
1891         if (err)
1892                 goto bad_unshare_out;
1893         /*
1894          * CLONE_NEWIPC must also detach from the undolist: after switching
1895          * to a new ipc namespace, the semaphore arrays from the old
1896          * namespace are unreachable.
1897          */
1898         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1899                 do_sysvsem = 1;
1900         err = unshare_fs(unshare_flags, &new_fs);
1901         if (err)
1902                 goto bad_unshare_out;
1903         err = unshare_fd(unshare_flags, &new_fd);
1904         if (err)
1905                 goto bad_unshare_cleanup_fs;
1906         err = unshare_userns(unshare_flags, &new_cred);
1907         if (err)
1908                 goto bad_unshare_cleanup_fd;
1909         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1910                                          new_cred, new_fs);
1911         if (err)
1912                 goto bad_unshare_cleanup_cred;
1913
1914         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1915                 if (do_sysvsem) {
1916                         /*
1917                          * CLONE_SYSVSEM is equivalent to sys_exit().
1918                          */
1919                         exit_sem(current);
1920                 }
1921
1922                 if (new_nsproxy)
1923                         switch_task_namespaces(current, new_nsproxy);
1924
1925                 task_lock(current);
1926
1927                 if (new_fs) {
1928                         fs = current->fs;
1929                         spin_lock(&fs->lock);
1930                         current->fs = new_fs;
1931                         if (--fs->users)
1932                                 new_fs = NULL;
1933                         else
1934                                 new_fs = fs;
1935                         spin_unlock(&fs->lock);
1936                 }
1937
1938                 if (new_fd) {
1939                         fd = current->files;
1940                         current->files = new_fd;
1941                         new_fd = fd;
1942                 }
1943
1944                 task_unlock(current);
1945
1946                 if (new_cred) {
1947                         /* Install the new user namespace */
1948                         commit_creds(new_cred);
1949                         new_cred = NULL;
1950                 }
1951         }
1952
1953 bad_unshare_cleanup_cred:
1954         if (new_cred)
1955                 put_cred(new_cred);
1956 bad_unshare_cleanup_fd:
1957         if (new_fd)
1958                 put_files_struct(new_fd);
1959
1960 bad_unshare_cleanup_fs:
1961         if (new_fs)
1962                 free_fs_struct(new_fs);
1963
1964 bad_unshare_out:
1965         return err;
1966 }
1967
1968 /*
1969  *      Helper to unshare the files of the current task.
1970  *      We don't want to expose copy_files internals to
1971  *      the exec layer of the kernel.
1972  */
1973
1974 int unshare_files(struct files_struct **displaced)
1975 {
1976         struct task_struct *task = current;
1977         struct files_struct *copy = NULL;
1978         int error;
1979
1980         error = unshare_fd(CLONE_FILES, &copy);
1981         if (error || !copy) {
1982                 *displaced = NULL;
1983                 return error;
1984         }
1985         *displaced = task->files;
1986         task_lock(task);
1987         task->files = copy;
1988         task_unlock(task);
1989         return 0;
1990 }