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/nsproxy.h>
  32 #include <linux/capability.h>
  33 #include <linux/cpu.h>
  34 #include <linux/cgroup.h>
  35 #include <linux/security.h>
  36 #include <linux/hugetlb.h>
  37 #include <linux/swap.h>
  38 #include <linux/syscalls.h>
  39 #include <linux/jiffies.h>
  40 #include <linux/tracehook.h>
  41 #include <linux/futex.h>
  42 #include <linux/compat.h>
  43 #include <linux/task_io_accounting_ops.h>
  44 #include <linux/rcupdate.h>
  45 #include <linux/ptrace.h>
  46 #include <linux/mount.h>
  47 #include <linux/audit.h>
  48 #include <linux/memcontrol.h>
  49 #include <linux/ftrace.h>
  50 #include <linux/profile.h>
  51 #include <linux/rmap.h>
  52 #include <linux/ksm.h>
  53 #include <linux/acct.h>
  54 #include <linux/tsacct_kern.h>
  55 #include <linux/cn_proc.h>
  56 #include <linux/freezer.h>
  57 #include <linux/delayacct.h>
  58 #include <linux/taskstats_kern.h>
  59 #include <linux/random.h>
  60 #include <linux/tty.h>
  61 #include <linux/proc_fs.h>
  62 #include <linux/blkdev.h>
  63 #include <linux/fs_struct.h>
  64 #include <linux/magic.h>
  65 #include <linux/perf_event.h>
  66 #include <linux/posix-timers.h>
  67 #include <linux/user-return-notifier.h>
  68 #include <linux/oom.h>
  69 #include <linux/khugepaged.h>
  70
  71 #include <asm/pgtable.h>
  72 #include <asm/pgalloc.h>
  73 #include <asm/uaccess.h>
  74 #include <asm/mmu_context.h>
  75 #include <asm/cacheflush.h>
  76 #include <asm/tlbflush.h>
  77
  78 #include <trace/events/sched.h>
  79
  80 /*
  81  * Protected counters by write_lock_irq(&tasklist_lock)
  82  */
  83 unsigned long total_forks;      /* Handle normal Linux uptimes. */
  84 int nr_threads;                 /* The idle threads do not count.. */
  85
  86 int max_threads;                /* tunable limit on nr_threads */
  87
  88 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
  89
  90 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
  91
  92 #ifdef CONFIG_PROVE_RCU
  93 int lockdep_tasklist_lock_is_held(void)
  94 {
  95         return lockdep_is_held(&tasklist_lock);
  96 }
  97 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
  98 #endif /* #ifdef CONFIG_PROVE_RCU */
  99
 100 int nr_processes(void)
 101 {
 102         int cpu;
 103         int total = 0;
 104
 105         for_each_possible_cpu(cpu)
 106                 total += per_cpu(process_counts, cpu);
 107
 108         return total;
 109 }
 110
 111 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
 112 # define alloc_task_struct()    kmem_cache_alloc(task_struct_cachep, GFP_KERNEL)
 113 # define free_task_struct(tsk)  kmem_cache_free(task_struct_cachep, (tsk))
 114 static struct kmem_cache *task_struct_cachep;
 115 #endif
 116
 117 #ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
 118 static inline struct thread_info *alloc_thread_info(struct task_struct *tsk)
 119 {
 120 #ifdef CONFIG_DEBUG_STACK_USAGE
 121         gfp_t mask = GFP_KERNEL | __GFP_ZERO;
 122 #else
 123         gfp_t mask = GFP_KERNEL;
 124 #endif
 125         return (struct thread_info *)__get_free_pages(mask, THREAD_SIZE_ORDER);
 126 }
 127
 128 static inline void free_thread_info(struct thread_info *ti)
 129 {
 130         free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 131 }
 132 #endif
 133
 134 /* SLAB cache for signal_struct structures (tsk->signal) */
 135 static struct kmem_cache *signal_cachep;
 136
 137 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 138 struct kmem_cache *sighand_cachep;
 139
 140 /* SLAB cache for files_struct structures (tsk->files) */
 141 struct kmem_cache *files_cachep;
 142
 143 /* SLAB cache for fs_struct structures (tsk->fs) */
 144 struct kmem_cache *fs_cachep;
 145
 146 /* SLAB cache for vm_area_struct structures */
 147 struct kmem_cache *vm_area_cachep;
 148
 149 /* SLAB cache for mm_struct structures (tsk->mm) */
 150 static struct kmem_cache *mm_cachep;
 151
 152 static void account_kernel_stack(struct thread_info *ti, int account)
 153 {
 154         struct zone *zone = page_zone(virt_to_page(ti));
 155
 156         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
 157 }
 158
 159 void free_task(struct task_struct *tsk)
 160 {
 161         prop_local_destroy_single(&tsk->dirties);
 162         account_kernel_stack(tsk->stack, -1);
 163         free_thread_info(tsk->stack);
 164         rt_mutex_debug_task_free(tsk);
 165         ftrace_graph_exit_task(tsk);
 166         free_task_struct(tsk);
 167 }
 168 EXPORT_SYMBOL(free_task);
 169
 170 static inline void free_signal_struct(struct signal_struct *sig)
 171 {
 172         taskstats_tgid_free(sig);
 173         sched_autogroup_exit(sig);
 174         kmem_cache_free(signal_cachep, sig);
 175 }
 176
 177 static inline void put_signal_struct(struct signal_struct *sig)
 178 {
 179         if (atomic_dec_and_test(&sig->sigcnt))
 180                 free_signal_struct(sig);
 181 }
 182
 183 void __put_task_struct(struct task_struct *tsk)
 184 {
 185         WARN_ON(!tsk->exit_state);
 186         WARN_ON(atomic_read(&tsk->usage));
 187         WARN_ON(tsk == current);
 188
 189         exit_creds(tsk);
 190         delayacct_tsk_free(tsk);
 191         put_signal_struct(tsk->signal);
 192
 193         if (!profile_handoff_task(tsk))
 194                 free_task(tsk);
 195 }
 196
 197 /*
 198  * macro override instead of weak attribute alias, to workaround
 199  * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
 200  */
 201 #ifndef arch_task_cache_init
 202 #define arch_task_cache_init()
 203 #endif
 204
 205 void __init fork_init(unsigned long mempages)
 206 {
 207 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
 208 #ifndef ARCH_MIN_TASKALIGN
 209 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
 210 #endif
 211         /* create a slab on which task_structs can be allocated */
 212         task_struct_cachep =
 213                 kmem_cache_create("task_struct", sizeof(struct task_struct),
 214                         ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
 215 #endif
 216
 217         /* do the arch specific task caches init */
 218         arch_task_cache_init();
 219
 220         /*
 221          * The default maximum number of threads is set to a safe
 222          * value: the thread structures can take up at most half
 223          * of memory.
 224          */
 225         max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
 226
 227         /*
 228          * we need to allow at least 20 threads to boot a system
 229          */
 230         if(max_threads < 20)
 231                 max_threads = 20;
 232
 233         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 234         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
 235         init_task.signal->rlim[RLIMIT_SIGPENDING] =
 236                 init_task.signal->rlim[RLIMIT_NPROC];
 237 }
 238
 239 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
 240                                                struct task_struct *src)
 241 {
 242         *dst = *src;
 243         return 0;
 244 }
 245
 246 static struct task_struct *dup_task_struct(struct task_struct *orig)
 247 {
 248         struct task_struct *tsk;
 249         struct thread_info *ti;
 250         unsigned long *stackend;
 251
 252         int err;
 253
 254         prepare_to_copy(orig);
 255
 256         tsk = alloc_task_struct();
 257         if (!tsk)
 258                 return NULL;
 259
 260         ti = alloc_thread_info(tsk);
 261         if (!ti) {
 262                 free_task_struct(tsk);
 263                 return NULL;
 264         }
 265
 266         err = arch_dup_task_struct(tsk, orig);
 267         if (err)
 268                 goto out;
 269
 270         tsk->stack = ti;
 271
 272         err = prop_local_init_single(&tsk->dirties);
 273         if (err)
 274                 goto out;
 275
 276         setup_thread_stack(tsk, orig);
 277         clear_user_return_notifier(tsk);
 278         clear_tsk_need_resched(tsk);
 279         stackend = end_of_stack(tsk);
 280         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 281
 282 #ifdef CONFIG_CC_STACKPROTECTOR
 283         tsk->stack_canary = get_random_int();
 284 #endif
 285
 286         /* One for us, one for whoever does the "release_task()" (usually parent) */
 287         atomic_set(&tsk->usage,2);
 288         atomic_set(&tsk->fs_excl, 0);
 289 #ifdef CONFIG_BLK_DEV_IO_TRACE
 290         tsk->btrace_seq = 0;
 291 #endif
 292         tsk->splice_pipe = NULL;
 293
 294         account_kernel_stack(ti, 1);
 295
 296         return tsk;
 297
 298 out:
 299         free_thread_info(ti);
 300         free_task_struct(tsk);
 301         return NULL;
 302 }
 303
 304 #ifdef CONFIG_MMU
 305 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 306 {
 307         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 308         struct rb_node **rb_link, *rb_parent;
 309         int retval;
 310         unsigned long charge;
 311         struct mempolicy *pol;
 312
 313         down_write(&oldmm->mmap_sem);
 314         flush_cache_dup_mm(oldmm);
 315         /*
 316          * Not linked in yet - no deadlock potential:
 317          */
 318         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 319
 320         mm->locked_vm = 0;
 321         mm->mmap = NULL;
 322         mm->mmap_cache = NULL;
 323         mm->free_area_cache = oldmm->mmap_base;
 324         mm->cached_hole_size = ~0UL;
 325         mm->map_count = 0;
 326         cpumask_clear(mm_cpumask(mm));
 327         mm->mm_rb = RB_ROOT;
 328         rb_link = &mm->mm_rb.rb_node;
 329         rb_parent = NULL;
 330         pprev = &mm->mmap;
 331         retval = ksm_fork(mm, oldmm);
 332         if (retval)
 333                 goto out;
 334         retval = khugepaged_fork(mm, oldmm);
 335         if (retval)
 336                 goto out;
 337
 338         prev = NULL;
 339         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 340                 struct file *file;
 341
 342                 if (mpnt->vm_flags & VM_DONTCOPY) {
 343                         long pages = vma_pages(mpnt);
 344                         mm->total_vm -= pages;
 345                         vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
 346                                                                 -pages);
 347                         continue;
 348                 }
 349                 charge = 0;
 350                 if (mpnt->vm_flags & VM_ACCOUNT) {
 351                         unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
 352                         if (security_vm_enough_memory(len))
 353                                 goto fail_nomem;
 354                         charge = len;
 355                 }
 356                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 357                 if (!tmp)
 358                         goto fail_nomem;
 359                 *tmp = *mpnt;
 360                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
 361                 pol = mpol_dup(vma_policy(mpnt));
 362                 retval = PTR_ERR(pol);
 363                 if (IS_ERR(pol))
 364                         goto fail_nomem_policy;
 365                 vma_set_policy(tmp, pol);
 366                 tmp->vm_mm = mm;
 367                 if (anon_vma_fork(tmp, mpnt))
 368                         goto fail_nomem_anon_vma_fork;
 369                 tmp->vm_flags &= ~VM_LOCKED;
 370                 tmp->vm_next = tmp->vm_prev = NULL;
 371                 file = tmp->vm_file;
 372                 if (file) {
 373                         struct inode *inode = file->f_path.dentry->d_inode;
 374                         struct address_space *mapping = file->f_mapping;
 375
 376                         get_file(file);
 377                         if (tmp->vm_flags & VM_DENYWRITE)
 378                                 atomic_dec(&inode->i_writecount);
 379                         spin_lock(&mapping->i_mmap_lock);
 380                         if (tmp->vm_flags & VM_SHARED)
 381                                 mapping->i_mmap_writable++;
 382                         tmp->vm_truncate_count = mpnt->vm_truncate_count;
 383                         flush_dcache_mmap_lock(mapping);
 384                         /* insert tmp into the share list, just after mpnt */
 385                         vma_prio_tree_add(tmp, mpnt);
 386                         flush_dcache_mmap_unlock(mapping);
 387                         spin_unlock(&mapping->i_mmap_lock);
 388                 }
 389
 390                 /*
 391                  * Clear hugetlb-related page reserves for children. This only
 392                  * affects MAP_PRIVATE mappings. Faults generated by the child
 393                  * are not guaranteed to succeed, even if read-only
 394                  */
 395                 if (is_vm_hugetlb_page(tmp))
 396                         reset_vma_resv_huge_pages(tmp);
 397
 398                 /*
 399                  * Link in the new vma and copy the page table entries.
 400                  */
 401                 *pprev = tmp;
 402                 pprev = &tmp->vm_next;
 403                 tmp->vm_prev = prev;
 404                 prev = tmp;
 405
 406                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 407                 rb_link = &tmp->vm_rb.rb_right;
 408                 rb_parent = &tmp->vm_rb;
 409
 410                 mm->map_count++;
 411                 retval = copy_page_range(mm, oldmm, mpnt);
 412
 413                 if (tmp->vm_ops && tmp->vm_ops->open)
 414                         tmp->vm_ops->open(tmp);
 415
 416                 if (retval)
 417                         goto out;
 418         }
 419         /* a new mm has just been created */
 420         arch_dup_mmap(oldmm, mm);
 421         retval = 0;
 422 out:
 423         up_write(&mm->mmap_sem);
 424         flush_tlb_mm(oldmm);
 425         up_write(&oldmm->mmap_sem);
 426         return retval;
 427 fail_nomem_anon_vma_fork:
 428         mpol_put(pol);
 429 fail_nomem_policy:
 430         kmem_cache_free(vm_area_cachep, tmp);
 431 fail_nomem:
 432         retval = -ENOMEM;
 433         vm_unacct_memory(charge);
 434         goto out;
 435 }
 436
 437 static inline int mm_alloc_pgd(struct mm_struct * mm)
 438 {
 439         mm->pgd = pgd_alloc(mm);
 440         if (unlikely(!mm->pgd))
 441                 return -ENOMEM;
 442         return 0;
 443 }
 444
 445 static inline void mm_free_pgd(struct mm_struct * mm)
 446 {
 447         pgd_free(mm, mm->pgd);
 448 }
 449 #else
 450 #define dup_mmap(mm, oldmm)     (0)
 451 #define mm_alloc_pgd(mm)        (0)
 452 #define mm_free_pgd(mm)
 453 #endif /* CONFIG_MMU */
 454
 455 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 456
 457 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 458 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 459
 460 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 461
 462 static int __init coredump_filter_setup(char *s)
 463 {
 464         default_dump_filter =
 465                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 466                 MMF_DUMP_FILTER_MASK;
 467         return 1;
 468 }
 469
 470 __setup("coredump_filter=", coredump_filter_setup);
 471
 472 #include <linux/init_task.h>
 473
 474 static void mm_init_aio(struct mm_struct *mm)
 475 {
 476 #ifdef CONFIG_AIO
 477         spin_lock_init(&mm->ioctx_lock);
 478         INIT_HLIST_HEAD(&mm->ioctx_list);
 479 #endif
 480 }
 481
 482 static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
 483 {
 484         atomic_set(&mm->mm_users, 1);
 485         atomic_set(&mm->mm_count, 1);
 486         init_rwsem(&mm->mmap_sem);
 487         INIT_LIST_HEAD(&mm->mmlist);
 488         mm->flags = (current->mm) ?
 489                 (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
 490         mm->core_state = NULL;
 491         mm->nr_ptes = 0;
 492         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 493         spin_lock_init(&mm->page_table_lock);
 494         mm->free_area_cache = TASK_UNMAPPED_BASE;
 495         mm->cached_hole_size = ~0UL;
 496         mm_init_aio(mm);
 497         mm_init_owner(mm, p);
 498         atomic_set(&mm->oom_disable_count, 0);
 499
 500         if (likely(!mm_alloc_pgd(mm))) {
 501                 mm->def_flags = 0;
 502                 mmu_notifier_mm_init(mm);
 503                 return mm;
 504         }
 505
 506         free_mm(mm);
 507         return NULL;
 508 }
 509
 510 /*
 511  * Allocate and initialize an mm_struct.
 512  */
 513 struct mm_struct * mm_alloc(void)
 514 {
 515         struct mm_struct * mm;
 516
 517         mm = allocate_mm();
 518         if (mm) {
 519                 memset(mm, 0, sizeof(*mm));
 520                 mm = mm_init(mm, current);
 521         }
 522         return mm;
 523 }
 524
 525 /*
 526  * Called when the last reference to the mm
 527  * is dropped: either by a lazy thread or by
 528  * mmput. Free the page directory and the mm.
 529  */
 530 void __mmdrop(struct mm_struct *mm)
 531 {
 532         BUG_ON(mm == &init_mm);
 533         mm_free_pgd(mm);
 534         destroy_context(mm);
 535         mmu_notifier_mm_destroy(mm);
 536 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 537         VM_BUG_ON(mm->pmd_huge_pte);
 538 #endif
 539         free_mm(mm);
 540 }
 541 EXPORT_SYMBOL_GPL(__mmdrop);
 542
 543 /*
 544  * Decrement the use count and release all resources for an mm.
 545  */
 546 void mmput(struct mm_struct *mm)
 547 {
 548         might_sleep();
 549
 550         if (atomic_dec_and_test(&mm->mm_users)) {
 551                 exit_aio(mm);
 552                 ksm_exit(mm);
 553                 khugepaged_exit(mm); /* must run before exit_mmap */
 554                 exit_mmap(mm);
 555                 set_mm_exe_file(mm, NULL);
 556                 if (!list_empty(&mm->mmlist)) {
 557                         spin_lock(&mmlist_lock);
 558                         list_del(&mm->mmlist);
 559                         spin_unlock(&mmlist_lock);
 560                 }
 561                 put_swap_token(mm);
 562                 if (mm->binfmt)
 563                         module_put(mm->binfmt->module);
 564                 mmdrop(mm);
 565         }
 566 }
 567 EXPORT_SYMBOL_GPL(mmput);
 568
 569 /**
 570  * get_task_mm - acquire a reference to the task's mm
 571  *
 572  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
 573  * this kernel workthread has transiently adopted a user mm with use_mm,
 574  * to do its AIO) is not set and if so returns a reference to it, after
 575  * bumping up the use count.  User must release the mm via mmput()
 576  * after use.  Typically used by /proc and ptrace.
 577  */
 578 struct mm_struct *get_task_mm(struct task_struct *task)
 579 {
 580         struct mm_struct *mm;
 581
 582         task_lock(task);
 583         mm = task->mm;
 584         if (mm) {
 585                 if (task->flags & PF_KTHREAD)
 586                         mm = NULL;
 587                 else
 588                         atomic_inc(&mm->mm_users);
 589         }
 590         task_unlock(task);
 591         return mm;
 592 }
 593 EXPORT_SYMBOL_GPL(get_task_mm);
 594
 595 /* Please note the differences between mmput and mm_release.
 596  * mmput is called whenever we stop holding onto a mm_struct,
 597  * error success whatever.
 598  *
 599  * mm_release is called after a mm_struct has been removed
 600  * from the current process.
 601  *
 602  * This difference is important for error handling, when we
 603  * only half set up a mm_struct for a new process and need to restore
 604  * the old one.  Because we mmput the new mm_struct before
 605  * restoring the old one. . .
 606  * Eric Biederman 10 January 1998
 607  */
 608 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 609 {
 610         struct completion *vfork_done = tsk->vfork_done;
 611
 612         /* Get rid of any futexes when releasing the mm */
 613 #ifdef CONFIG_FUTEX
 614         if (unlikely(tsk->robust_list)) {
 615                 exit_robust_list(tsk);
 616                 tsk->robust_list = NULL;
 617         }
 618 #ifdef CONFIG_COMPAT
 619         if (unlikely(tsk->compat_robust_list)) {
 620                 compat_exit_robust_list(tsk);
 621                 tsk->compat_robust_list = NULL;
 622         }
 623 #endif
 624         if (unlikely(!list_empty(&tsk->pi_state_list)))
 625                 exit_pi_state_list(tsk);
 626 #endif
 627
 628         /* Get rid of any cached register state */
 629         deactivate_mm(tsk, mm);
 630
 631         /* notify parent sleeping on vfork() */
 632         if (vfork_done) {
 633                 tsk->vfork_done = NULL;
 634                 complete(vfork_done);
 635         }
 636
 637         /*
 638          * If we're exiting normally, clear a user-space tid field if
 639          * requested.  We leave this alone when dying by signal, to leave
 640          * the value intact in a core dump, and to save the unnecessary
 641          * trouble otherwise.  Userland only wants this done for a sys_exit.
 642          */
 643         if (tsk->clear_child_tid) {
 644                 if (!(tsk->flags & PF_SIGNALED) &&
 645                     atomic_read(&mm->mm_users) > 1) {
 646                         /*
 647                          * We don't check the error code - if userspace has
 648                          * not set up a proper pointer then tough luck.
 649                          */
 650                         put_user(0, tsk->clear_child_tid);
 651                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
 652                                         1, NULL, NULL, 0);
 653                 }
 654                 tsk->clear_child_tid = NULL;
 655         }
 656 }
 657
 658 /*
 659  * Allocate a new mm structure and copy contents from the
 660  * mm structure of the passed in task structure.
 661  */
 662 struct mm_struct *dup_mm(struct task_struct *tsk)
 663 {
 664         struct mm_struct *mm, *oldmm = current->mm;
 665         int err;
 666
 667         if (!oldmm)
 668                 return NULL;
 669
 670         mm = allocate_mm();
 671         if (!mm)
 672                 goto fail_nomem;
 673
 674         memcpy(mm, oldmm, sizeof(*mm));
 675
 676         /* Initializing for Swap token stuff */
 677         mm->token_priority = 0;
 678         mm->last_interval = 0;
 679
 680 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 681         mm->pmd_huge_pte = NULL;
 682 #endif
 683
 684         if (!mm_init(mm, tsk))
 685                 goto fail_nomem;
 686
 687         if (init_new_context(tsk, mm))
 688                 goto fail_nocontext;
 689
 690         dup_mm_exe_file(oldmm, mm);
 691
 692         err = dup_mmap(mm, oldmm);
 693         if (err)
 694                 goto free_pt;
 695
 696         mm->hiwater_rss = get_mm_rss(mm);
 697         mm->hiwater_vm = mm->total_vm;
 698
 699         if (mm->binfmt && !try_module_get(mm->binfmt->module))
 700                 goto free_pt;
 701
 702         return mm;
 703
 704 free_pt:
 705         /* don't put binfmt in mmput, we haven't got module yet */
 706         mm->binfmt = NULL;
 707         mmput(mm);
 708
 709 fail_nomem:
 710         return NULL;
 711
 712 fail_nocontext:
 713         /*
 714          * If init_new_context() failed, we cannot use mmput() to free the mm
 715          * because it calls destroy_context()
 716          */
 717         mm_free_pgd(mm);
 718         free_mm(mm);
 719         return NULL;
 720 }
 721
 722 static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
 723 {
 724         struct mm_struct * mm, *oldmm;
 725         int retval;
 726
 727         tsk->min_flt = tsk->maj_flt = 0;
 728         tsk->nvcsw = tsk->nivcsw = 0;
 729 #ifdef CONFIG_DETECT_HUNG_TASK
 730         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 731 #endif
 732
 733         tsk->mm = NULL;
 734         tsk->active_mm = NULL;
 735
 736         /*
 737          * Are we cloning a kernel thread?
 738          *
 739          * We need to steal a active VM for that..
 740          */
 741         oldmm = current->mm;
 742         if (!oldmm)
 743                 return 0;
 744
 745         if (clone_flags & CLONE_VM) {
 746                 atomic_inc(&oldmm->mm_users);
 747                 mm = oldmm;
 748                 goto good_mm;
 749         }
 750
 751         retval = -ENOMEM;
 752         mm = dup_mm(tsk);
 753         if (!mm)
 754                 goto fail_nomem;
 755
 756 good_mm:
 757         /* Initializing for Swap token stuff */
 758         mm->token_priority = 0;
 759         mm->last_interval = 0;
 760         if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
 761                 atomic_inc(&mm->oom_disable_count);
 762
 763         tsk->mm = mm;
 764         tsk->active_mm = mm;
 765         return 0;
 766
 767 fail_nomem:
 768         return retval;
 769 }
 770
 771 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 772 {
 773         struct fs_struct *fs = current->fs;
 774         if (clone_flags & CLONE_FS) {
 775                 /* tsk->fs is already what we want */
 776                 spin_lock(&fs->lock);
 777                 if (fs->in_exec) {
 778                         spin_unlock(&fs->lock);
 779                         return -EAGAIN;
 780                 }
 781                 fs->users++;
 782                 spin_unlock(&fs->lock);
 783                 return 0;
 784         }
 785         tsk->fs = copy_fs_struct(fs);
 786         if (!tsk->fs)
 787                 return -ENOMEM;
 788         return 0;
 789 }
 790
 791 static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
 792 {
 793         struct files_struct *oldf, *newf;
 794         int error = 0;
 795
 796         /*
 797          * A background process may not have any files ...
 798          */
 799         oldf = current->files;
 800         if (!oldf)
 801                 goto out;
 802
 803         if (clone_flags & CLONE_FILES) {
 804                 atomic_inc(&oldf->count);
 805                 goto out;
 806         }
 807
 808         newf = dup_fd(oldf, &error);
 809         if (!newf)
 810                 goto out;
 811
 812         tsk->files = newf;
 813         error = 0;
 814 out:
 815         return error;
 816 }
 817
 818 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 819 {
 820 #ifdef CONFIG_BLOCK
 821         struct io_context *ioc = current->io_context;
 822
 823         if (!ioc)
 824                 return 0;
 825         /*
 826          * Share io context with parent, if CLONE_IO is set
 827          */
 828         if (clone_flags & CLONE_IO) {
 829                 tsk->io_context = ioc_task_link(ioc);
 830                 if (unlikely(!tsk->io_context))
 831                         return -ENOMEM;
 832         } else if (ioprio_valid(ioc->ioprio)) {
 833                 tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
 834                 if (unlikely(!tsk->io_context))
 835                         return -ENOMEM;
 836
 837                 tsk->io_context->ioprio = ioc->ioprio;
 838         }
 839 #endif
 840         return 0;
 841 }
 842
 843 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 844 {
 845         struct sighand_struct *sig;
 846
 847         if (clone_flags & CLONE_SIGHAND) {
 848                 atomic_inc(&current->sighand->count);
 849                 return 0;
 850         }
 851         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
 852         rcu_assign_pointer(tsk->sighand, sig);
 853         if (!sig)
 854                 return -ENOMEM;
 855         atomic_set(&sig->count, 1);
 856         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
 857         return 0;
 858 }
 859
 860 void __cleanup_sighand(struct sighand_struct *sighand)
 861 {
 862         if (atomic_dec_and_test(&sighand->count))
 863                 kmem_cache_free(sighand_cachep, sighand);
 864 }
 865
 866
 867 /*
 868  * Initialize POSIX timer handling for a thread group.
 869  */
 870 static void posix_cpu_timers_init_group(struct signal_struct *sig)
 871 {
 872         unsigned long cpu_limit;
 873
 874         /* Thread group counters. */
 875         thread_group_cputime_init(sig);
 876
 877         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
 878         if (cpu_limit != RLIM_INFINITY) {
 879                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
 880                 sig->cputimer.running = 1;
 881         }
 882
 883         /* The timer lists. */
 884         INIT_LIST_HEAD(&sig->cpu_timers[0]);
 885         INIT_LIST_HEAD(&sig->cpu_timers[1]);
 886         INIT_LIST_HEAD(&sig->cpu_timers[2]);
 887 }
 888
 889 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 890 {
 891         struct signal_struct *sig;
 892
 893         if (clone_flags & CLONE_THREAD)
 894                 return 0;
 895
 896         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
 897         tsk->signal = sig;
 898         if (!sig)
 899                 return -ENOMEM;
 900
 901         sig->nr_threads = 1;
 902         atomic_set(&sig->live, 1);
 903         atomic_set(&sig->sigcnt, 1);
 904         init_waitqueue_head(&sig->wait_chldexit);
 905         if (clone_flags & CLONE_NEWPID)
 906                 sig->flags |= SIGNAL_UNKILLABLE;
 907         sig->curr_target = tsk;
 908         init_sigpending(&sig->shared_pending);
 909         INIT_LIST_HEAD(&sig->posix_timers);
 910
 911         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 912         sig->real_timer.function = it_real_fn;
 913
 914         task_lock(current->group_leader);
 915         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
 916         task_unlock(current->group_leader);
 917
 918         posix_cpu_timers_init_group(sig);
 919
 920         tty_audit_fork(sig);
 921         sched_autogroup_fork(sig);
 922
 923         sig->oom_adj = current->signal->oom_adj;
 924         sig->oom_score_adj = current->signal->oom_score_adj;
 925         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
 926
 927         mutex_init(&sig->cred_guard_mutex);
 928
 929         return 0;
 930 }
 931
 932 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
 933 {
 934         unsigned long new_flags = p->flags;
 935
 936         new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
 937         new_flags |= PF_FORKNOEXEC;
 938         new_flags |= PF_STARTING;
 939         p->flags = new_flags;
 940         clear_freeze_flag(p);
 941 }
 942
 943 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
 944 {
 945         current->clear_child_tid = tidptr;
 946
 947         return task_pid_vnr(current);
 948 }
 949
 950 static void rt_mutex_init_task(struct task_struct *p)
 951 {
 952         raw_spin_lock_init(&p->pi_lock);
 953 #ifdef CONFIG_RT_MUTEXES
 954         plist_head_init_raw(&p->pi_waiters, &p->pi_lock);
 955         p->pi_blocked_on = NULL;
 956 #endif
 957 }
 958
 959 #ifdef CONFIG_MM_OWNER
 960 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
 961 {
 962         mm->owner = p;
 963 }
 964 #endif /* CONFIG_MM_OWNER */
 965
 966 /*
 967  * Initialize POSIX timer handling for a single task.
 968  */
 969 static void posix_cpu_timers_init(struct task_struct *tsk)
 970 {
 971         tsk->cputime_expires.prof_exp = cputime_zero;
 972         tsk->cputime_expires.virt_exp = cputime_zero;
 973         tsk->cputime_expires.sched_exp = 0;
 974         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
 975         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
 976         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
 977 }
 978
 979 /*
 980  * This creates a new process as a copy of the old one,
 981  * but does not actually start it yet.
 982  *
 983  * It copies the registers, and all the appropriate
 984  * parts of the process environment (as per the clone
 985  * flags). The actual kick-off is left to the caller.
 986  */
 987 static struct task_struct *copy_process(unsigned long clone_flags,
 988                                         unsigned long stack_start,
 989                                         struct pt_regs *regs,
 990                                         unsigned long stack_size,
 991                                         int __user *child_tidptr,
 992                                         struct pid *pid,
 993                                         int trace)
 994 {
 995         int retval;
 996         struct task_struct *p;
 997         int cgroup_callbacks_done = 0;
 998
 999         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1000                 return ERR_PTR(-EINVAL);
1001
1002         /*
1003          * Thread groups must share signals as well, and detached threads
1004          * can only be started up within the thread group.
1005          */
1006         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1007                 return ERR_PTR(-EINVAL);
1008
1009         /*
1010          * Shared signal handlers imply shared VM. By way of the above,
1011          * thread groups also imply shared VM. Blocking this case allows
1012          * for various simplifications in other code.
1013          */
1014         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1015                 return ERR_PTR(-EINVAL);
1016
1017         /*
1018          * Siblings of global init remain as zombies on exit since they are
1019          * not reaped by their parent (swapper). To solve this and to avoid
1020          * multi-rooted process trees, prevent global and container-inits
1021          * from creating siblings.
1022          */
1023         if ((clone_flags & CLONE_PARENT) &&
1024                                 current->signal->flags & SIGNAL_UNKILLABLE)
1025                 return ERR_PTR(-EINVAL);
1026
1027         retval = security_task_create(clone_flags);
1028         if (retval)
1029                 goto fork_out;
1030
1031         retval = -ENOMEM;
1032         p = dup_task_struct(current);
1033         if (!p)
1034                 goto fork_out;
1035
1036         ftrace_graph_init_task(p);
1037
1038         rt_mutex_init_task(p);
1039
1040 #ifdef CONFIG_PROVE_LOCKING
1041         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1042         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1043 #endif
1044         retval = -EAGAIN;
1045         if (atomic_read(&p->real_cred->user->processes) >=
1046                         task_rlimit(p, RLIMIT_NPROC)) {
1047                 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1048                     p->real_cred->user != INIT_USER)
1049                         goto bad_fork_free;
1050         }
1051
1052         retval = copy_creds(p, clone_flags);
1053         if (retval < 0)
1054                 goto bad_fork_free;
1055
1056         /*
1057          * If multiple threads are within copy_process(), then this check
1058          * triggers too late. This doesn't hurt, the check is only there
1059          * to stop root fork bombs.
1060          */
1061         retval = -EAGAIN;
1062         if (nr_threads >= max_threads)
1063                 goto bad_fork_cleanup_count;
1064
1065         if (!try_module_get(task_thread_info(p)->exec_domain->module))
1066                 goto bad_fork_cleanup_count;
1067
1068         p->did_exec = 0;
1069         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1070         copy_flags(clone_flags, p);
1071         INIT_LIST_HEAD(&p->children);
1072         INIT_LIST_HEAD(&p->sibling);
1073         rcu_copy_process(p);
1074         p->vfork_done = NULL;
1075         spin_lock_init(&p->alloc_lock);
1076
1077         init_sigpending(&p->pending);
1078
1079         p->utime = cputime_zero;
1080         p->stime = cputime_zero;
1081         p->gtime = cputime_zero;
1082         p->utimescaled = cputime_zero;
1083         p->stimescaled = cputime_zero;
1084 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
1085         p->prev_utime = cputime_zero;
1086         p->prev_stime = cputime_zero;
1087 #endif
1088 #if defined(SPLIT_RSS_COUNTING)
1089         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1090 #endif
1091
1092         p->default_timer_slack_ns = current->timer_slack_ns;
1093
1094         task_io_accounting_init(&p->ioac);
1095         acct_clear_integrals(p);
1096
1097         posix_cpu_timers_init(p);
1098
1099         p->lock_depth = -1;             /* -1 = no lock */
1100         do_posix_clock_monotonic_gettime(&p->start_time);
1101         p->real_start_time = p->start_time;
1102         monotonic_to_bootbased(&p->real_start_time);
1103         p->io_context = NULL;
1104         p->audit_context = NULL;
1105         cgroup_fork(p);
1106 #ifdef CONFIG_NUMA
1107         p->mempolicy = mpol_dup(p->mempolicy);
1108         if (IS_ERR(p->mempolicy)) {
1109                 retval = PTR_ERR(p->mempolicy);
1110                 p->mempolicy = NULL;
1111                 goto bad_fork_cleanup_cgroup;
1112         }
1113         mpol_fix_fork_child_flag(p);
1114 #endif
1115 #ifdef CONFIG_TRACE_IRQFLAGS
1116         p->irq_events = 0;
1117 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1118         p->hardirqs_enabled = 1;
1119 #else
1120         p->hardirqs_enabled = 0;
1121 #endif
1122         p->hardirq_enable_ip = 0;
1123         p->hardirq_enable_event = 0;
1124         p->hardirq_disable_ip = _THIS_IP_;
1125         p->hardirq_disable_event = 0;
1126         p->softirqs_enabled = 1;
1127         p->softirq_enable_ip = _THIS_IP_;
1128         p->softirq_enable_event = 0;
1129         p->softirq_disable_ip = 0;
1130         p->softirq_disable_event = 0;
1131         p->hardirq_context = 0;
1132         p->softirq_context = 0;
1133 #endif
1134 #ifdef CONFIG_LOCKDEP
1135         p->lockdep_depth = 0; /* no locks held yet */
1136         p->curr_chain_key = 0;
1137         p->lockdep_recursion = 0;
1138 #endif
1139
1140 #ifdef CONFIG_DEBUG_MUTEXES
1141         p->blocked_on = NULL; /* not blocked yet */
1142 #endif
1143 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1144         p->memcg_batch.do_batch = 0;
1145         p->memcg_batch.memcg = NULL;
1146 #endif
1147
1148         /* Perform scheduler related setup. Assign this task to a CPU. */
1149         sched_fork(p, clone_flags);
1150
1151         retval = perf_event_init_task(p);
1152         if (retval)
1153                 goto bad_fork_cleanup_policy;
1154
1155         if ((retval = audit_alloc(p)))
1156                 goto bad_fork_cleanup_policy;
1157         /* copy all the process information */
1158         if ((retval = copy_semundo(clone_flags, p)))
1159                 goto bad_fork_cleanup_audit;
1160         if ((retval = copy_files(clone_flags, p)))
1161                 goto bad_fork_cleanup_semundo;
1162         if ((retval = copy_fs(clone_flags, p)))
1163                 goto bad_fork_cleanup_files;
1164         if ((retval = copy_sighand(clone_flags, p)))
1165                 goto bad_fork_cleanup_fs;
1166         if ((retval = copy_signal(clone_flags, p)))
1167                 goto bad_fork_cleanup_sighand;
1168         if ((retval = copy_mm(clone_flags, p)))
1169                 goto bad_fork_cleanup_signal;
1170         if ((retval = copy_namespaces(clone_flags, p)))
1171                 goto bad_fork_cleanup_mm;
1172         if ((retval = copy_io(clone_flags, p)))
1173                 goto bad_fork_cleanup_namespaces;
1174         retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1175         if (retval)
1176                 goto bad_fork_cleanup_io;
1177
1178         if (pid != &init_struct_pid) {
1179                 retval = -ENOMEM;
1180                 pid = alloc_pid(p->nsproxy->pid_ns);
1181                 if (!pid)
1182                         goto bad_fork_cleanup_io;
1183
1184                 if (clone_flags & CLONE_NEWPID) {
1185                         retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
1186                         if (retval < 0)
1187                                 goto bad_fork_free_pid;
1188                 }
1189         }
1190
1191         p->pid = pid_nr(pid);
1192         p->tgid = p->pid;
1193         if (clone_flags & CLONE_THREAD)
1194                 p->tgid = current->tgid;
1195
1196         if (current->nsproxy != p->nsproxy) {
1197                 retval = ns_cgroup_clone(p, pid);
1198                 if (retval)
1199                         goto bad_fork_free_pid;
1200         }
1201
1202         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1203         /*
1204          * Clear TID on mm_release()?
1205          */
1206         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1207 #ifdef CONFIG_FUTEX
1208         p->robust_list = NULL;
1209 #ifdef CONFIG_COMPAT
1210         p->compat_robust_list = NULL;
1211 #endif
1212         INIT_LIST_HEAD(&p->pi_state_list);
1213         p->pi_state_cache = NULL;
1214 #endif
1215         /*
1216          * sigaltstack should be cleared when sharing the same VM
1217          */
1218         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1219                 p->sas_ss_sp = p->sas_ss_size = 0;
1220
1221         /*
1222          * Syscall tracing and stepping should be turned off in the
1223          * child regardless of CLONE_PTRACE.
1224          */
1225         user_disable_single_step(p);
1226         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1227 #ifdef TIF_SYSCALL_EMU
1228         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1229 #endif
1230         clear_all_latency_tracing(p);
1231
1232         /* ok, now we should be set up.. */
1233         p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1234         p->pdeath_signal = 0;
1235         p->exit_state = 0;
1236
1237         /*
1238          * Ok, make it visible to the rest of the system.
1239          * We dont wake it up yet.
1240          */
1241         p->group_leader = p;
1242         INIT_LIST_HEAD(&p->thread_group);
1243
1244         /* Now that the task is set up, run cgroup callbacks if
1245          * necessary. We need to run them before the task is visible
1246          * on the tasklist. */
1247         cgroup_fork_callbacks(p);
1248         cgroup_callbacks_done = 1;
1249
1250         /* Need tasklist lock for parent etc handling! */
1251         write_lock_irq(&tasklist_lock);
1252
1253         /* CLONE_PARENT re-uses the old parent */
1254         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1255                 p->real_parent = current->real_parent;
1256                 p->parent_exec_id = current->parent_exec_id;
1257         } else {
1258                 p->real_parent = current;
1259                 p->parent_exec_id = current->self_exec_id;
1260         }
1261
1262         spin_lock(&current->sighand->siglock);
1263
1264         /*
1265          * Process group and session signals need to be delivered to just the
1266          * parent before the fork or both the parent and the child after the
1267          * fork. Restart if a signal comes in before we add the new process to
1268          * it's process group.
1269          * A fatal signal pending means that current will exit, so the new
1270          * thread can't slip out of an OOM kill (or normal SIGKILL).
1271          */
1272         recalc_sigpending();
1273         if (signal_pending(current)) {
1274                 spin_unlock(&current->sighand->siglock);
1275                 write_unlock_irq(&tasklist_lock);
1276                 retval = -ERESTARTNOINTR;
1277                 goto bad_fork_free_pid;
1278         }
1279
1280         if (clone_flags & CLONE_THREAD) {
1281                 current->signal->nr_threads++;
1282                 atomic_inc(&current->signal->live);
1283                 atomic_inc(&current->signal->sigcnt);
1284                 p->group_leader = current->group_leader;
1285                 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1286         }
1287
1288         if (likely(p->pid)) {
1289                 tracehook_finish_clone(p, clone_flags, trace);
1290
1291                 if (thread_group_leader(p)) {
1292                         if (clone_flags & CLONE_NEWPID)
1293                                 p->nsproxy->pid_ns->child_reaper = p;
1294
1295                         p->signal->leader_pid = pid;
1296                         p->signal->tty = tty_kref_get(current->signal->tty);
1297                         attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1298                         attach_pid(p, PIDTYPE_SID, task_session(current));
1299                         list_add_tail(&p->sibling, &p->real_parent->children);
1300                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1301                         __this_cpu_inc(process_counts);
1302                 }
1303                 attach_pid(p, PIDTYPE_PID, pid);
1304                 nr_threads++;
1305         }
1306
1307         total_forks++;
1308         spin_unlock(&current->sighand->siglock);
1309         write_unlock_irq(&tasklist_lock);
1310         proc_fork_connector(p);
1311         cgroup_post_fork(p);
1312         perf_event_fork(p);
1313         return p;
1314
1315 bad_fork_free_pid:
1316         if (pid != &init_struct_pid)
1317                 free_pid(pid);
1318 bad_fork_cleanup_io:
1319         if (p->io_context)
1320                 exit_io_context(p);
1321 bad_fork_cleanup_namespaces:
1322         exit_task_namespaces(p);
1323 bad_fork_cleanup_mm:
1324         if (p->mm) {
1325                 task_lock(p);
1326                 if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
1327                         atomic_dec(&p->mm->oom_disable_count);
1328                 task_unlock(p);
1329                 mmput(p->mm);
1330         }
1331 bad_fork_cleanup_signal:
1332         if (!(clone_flags & CLONE_THREAD))
1333                 free_signal_struct(p->signal);
1334 bad_fork_cleanup_sighand:
1335         __cleanup_sighand(p->sighand);
1336 bad_fork_cleanup_fs:
1337         exit_fs(p); /* blocking */
1338 bad_fork_cleanup_files:
1339         exit_files(p); /* blocking */
1340 bad_fork_cleanup_semundo:
1341         exit_sem(p);
1342 bad_fork_cleanup_audit:
1343         audit_free(p);
1344 bad_fork_cleanup_policy:
1345         perf_event_free_task(p);
1346 #ifdef CONFIG_NUMA
1347         mpol_put(p->mempolicy);
1348 bad_fork_cleanup_cgroup:
1349 #endif
1350         cgroup_exit(p, cgroup_callbacks_done);
1351         delayacct_tsk_free(p);
1352         module_put(task_thread_info(p)->exec_domain->module);
1353 bad_fork_cleanup_count:
1354         atomic_dec(&p->cred->user->processes);
1355         exit_creds(p);
1356 bad_fork_free:
1357         free_task(p);
1358 fork_out:
1359         return ERR_PTR(retval);
1360 }
1361
1362 noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1363 {
1364         memset(regs, 0, sizeof(struct pt_regs));
1365         return regs;
1366 }
1367
1368 static inline void init_idle_pids(struct pid_link *links)
1369 {
1370         enum pid_type type;
1371
1372         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1373                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1374                 links[type].pid = &init_struct_pid;
1375         }
1376 }
1377
1378 struct task_struct * __cpuinit fork_idle(int cpu)
1379 {
1380         struct task_struct *task;
1381         struct pt_regs regs;
1382
1383         task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
1384                             &init_struct_pid, 0);
1385         if (!IS_ERR(task)) {
1386                 init_idle_pids(task->pids);
1387                 init_idle(task, cpu);
1388         }
1389
1390         return task;
1391 }
1392
1393 /*
1394  *  Ok, this is the main fork-routine.
1395  *
1396  * It copies the process, and if successful kick-starts
1397  * it and waits for it to finish using the VM if required.
1398  */
1399 long do_fork(unsigned long clone_flags,
1400               unsigned long stack_start,
1401               struct pt_regs *regs,
1402               unsigned long stack_size,
1403               int __user *parent_tidptr,
1404               int __user *child_tidptr)
1405 {
1406         struct task_struct *p;
1407         int trace = 0;
1408         long nr;
1409
1410         /*
1411          * Do some preliminary argument and permissions checking before we
1412          * actually start allocating stuff
1413          */
1414         if (clone_flags & CLONE_NEWUSER) {
1415                 if (clone_flags & CLONE_THREAD)
1416                         return -EINVAL;
1417                 /* hopefully this check will go away when userns support is
1418                  * complete
1419                  */
1420                 if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1421                                 !capable(CAP_SETGID))
1422                         return -EPERM;
1423         }
1424
1425         /*
1426          * When called from kernel_thread, don't do user tracing stuff.
1427          */
1428         if (likely(user_mode(regs)))
1429                 trace = tracehook_prepare_clone(clone_flags);
1430
1431         p = copy_process(clone_flags, stack_start, regs, stack_size,
1432                          child_tidptr, NULL, trace);
1433         /*
1434          * Do this prior waking up the new thread - the thread pointer
1435          * might get invalid after that point, if the thread exits quickly.
1436          */
1437         if (!IS_ERR(p)) {
1438                 struct completion vfork;
1439
1440                 trace_sched_process_fork(current, p);
1441
1442                 nr = task_pid_vnr(p);
1443
1444                 if (clone_flags & CLONE_PARENT_SETTID)
1445                         put_user(nr, parent_tidptr);
1446
1447                 if (clone_flags & CLONE_VFORK) {
1448                         p->vfork_done = &vfork;
1449                         init_completion(&vfork);
1450                 }
1451
1452                 audit_finish_fork(p);
1453                 tracehook_report_clone(regs, clone_flags, nr, p);
1454
1455                 /*
1456                  * We set PF_STARTING at creation in case tracing wants to
1457                  * use this to distinguish a fully live task from one that
1458                  * hasn't gotten to tracehook_report_clone() yet.  Now we
1459                  * clear it and set the child going.
1460                  */
1461                 p->flags &= ~PF_STARTING;
1462
1463                 wake_up_new_task(p, clone_flags);
1464
1465                 tracehook_report_clone_complete(trace, regs,
1466                                                 clone_flags, nr, p);
1467
1468                 if (clone_flags & CLONE_VFORK) {
1469                         freezer_do_not_count();
1470                         wait_for_completion(&vfork);
1471                         freezer_count();
1472                         tracehook_report_vfork_done(p, nr);
1473                 }
1474         } else {
1475                 nr = PTR_ERR(p);
1476         }
1477         return nr;
1478 }
1479
1480 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1481 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1482 #endif
1483
1484 static void sighand_ctor(void *data)
1485 {
1486         struct sighand_struct *sighand = data;
1487
1488         spin_lock_init(&sighand->siglock);
1489         init_waitqueue_head(&sighand->signalfd_wqh);
1490 }
1491
1492 void __init proc_caches_init(void)
1493 {
1494         sighand_cachep = kmem_cache_create("sighand_cache",
1495                         sizeof(struct sighand_struct), 0,
1496                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1497                         SLAB_NOTRACK, sighand_ctor);
1498         signal_cachep = kmem_cache_create("signal_cache",
1499                         sizeof(struct signal_struct), 0,
1500                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1501         files_cachep = kmem_cache_create("files_cache",
1502                         sizeof(struct files_struct), 0,
1503                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1504         fs_cachep = kmem_cache_create("fs_cache",
1505                         sizeof(struct fs_struct), 0,
1506                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1507         mm_cachep = kmem_cache_create("mm_struct",
1508                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1509                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1510         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1511         mmap_init();
1512 }
1513
1514 /*
1515  * Check constraints on flags passed to the unshare system call and
1516  * force unsharing of additional process context as appropriate.
1517  */
1518 static void check_unshare_flags(unsigned long *flags_ptr)
1519 {
1520         /*
1521          * If unsharing a thread from a thread group, must also
1522          * unshare vm.
1523          */
1524         if (*flags_ptr & CLONE_THREAD)
1525                 *flags_ptr |= CLONE_VM;
1526
1527         /*
1528          * If unsharing vm, must also unshare signal handlers.
1529          */
1530         if (*flags_ptr & CLONE_VM)
1531                 *flags_ptr |= CLONE_SIGHAND;
1532
1533         /*
1534          * If unsharing namespace, must also unshare filesystem information.
1535          */
1536         if (*flags_ptr & CLONE_NEWNS)
1537                 *flags_ptr |= CLONE_FS;
1538 }
1539
1540 /*
1541  * Unsharing of tasks created with CLONE_THREAD is not supported yet
1542  */
1543 static int unshare_thread(unsigned long unshare_flags)
1544 {
1545         if (unshare_flags & CLONE_THREAD)
1546                 return -EINVAL;
1547
1548         return 0;
1549 }
1550
1551 /*
1552  * Unshare the filesystem structure if it is being shared
1553  */
1554 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1555 {
1556         struct fs_struct *fs = current->fs;
1557
1558         if (!(unshare_flags & CLONE_FS) || !fs)
1559                 return 0;
1560
1561         /* don't need lock here; in the worst case we'll do useless copy */
1562         if (fs->users == 1)
1563                 return 0;
1564
1565         *new_fsp = copy_fs_struct(fs);
1566         if (!*new_fsp)
1567                 return -ENOMEM;
1568
1569         return 0;
1570 }
1571
1572 /*
1573  * Unsharing of sighand is not supported yet
1574  */
1575 static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
1576 {
1577         struct sighand_struct *sigh = current->sighand;
1578
1579         if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)
1580                 return -EINVAL;
1581         else
1582                 return 0;
1583 }
1584
1585 /*
1586  * Unshare vm if it is being shared
1587  */
1588 static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
1589 {
1590         struct mm_struct *mm = current->mm;
1591
1592         if ((unshare_flags & CLONE_VM) &&
1593             (mm && atomic_read(&mm->mm_users) > 1)) {
1594                 return -EINVAL;
1595         }
1596
1597         return 0;
1598 }
1599
1600 /*
1601  * Unshare file descriptor table if it is being shared
1602  */
1603 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1604 {
1605         struct files_struct *fd = current->files;
1606         int error = 0;
1607
1608         if ((unshare_flags & CLONE_FILES) &&
1609             (fd && atomic_read(&fd->count) > 1)) {
1610                 *new_fdp = dup_fd(fd, &error);
1611                 if (!*new_fdp)
1612                         return error;
1613         }
1614
1615         return 0;
1616 }
1617
1618 /*
1619  * unshare allows a process to 'unshare' part of the process
1620  * context which was originally shared using clone.  copy_*
1621  * functions used by do_fork() cannot be used here directly
1622  * because they modify an inactive task_struct that is being
1623  * constructed. Here we are modifying the current, active,
1624  * task_struct.
1625  */
1626 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1627 {
1628         int err = 0;
1629         struct fs_struct *fs, *new_fs = NULL;
1630         struct sighand_struct *new_sigh = NULL;
1631         struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
1632         struct files_struct *fd, *new_fd = NULL;
1633         struct nsproxy *new_nsproxy = NULL;
1634         int do_sysvsem = 0;
1635
1636         check_unshare_flags(&unshare_flags);
1637
1638         /* Return -EINVAL for all unsupported flags */
1639         err = -EINVAL;
1640         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1641                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1642                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1643                 goto bad_unshare_out;
1644
1645         /*
1646          * CLONE_NEWIPC must also detach from the undolist: after switching
1647          * to a new ipc namespace, the semaphore arrays from the old
1648          * namespace are unreachable.
1649          */
1650         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1651                 do_sysvsem = 1;
1652         if ((err = unshare_thread(unshare_flags)))
1653                 goto bad_unshare_out;
1654         if ((err = unshare_fs(unshare_flags, &new_fs)))
1655                 goto bad_unshare_cleanup_thread;
1656         if ((err = unshare_sighand(unshare_flags, &new_sigh)))
1657                 goto bad_unshare_cleanup_fs;
1658         if ((err = unshare_vm(unshare_flags, &new_mm)))
1659                 goto bad_unshare_cleanup_sigh;
1660         if ((err = unshare_fd(unshare_flags, &new_fd)))
1661                 goto bad_unshare_cleanup_vm;
1662         if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1663                         new_fs)))
1664                 goto bad_unshare_cleanup_fd;
1665
1666         if (new_fs ||  new_mm || new_fd || do_sysvsem || new_nsproxy) {
1667                 if (do_sysvsem) {
1668                         /*
1669                          * CLONE_SYSVSEM is equivalent to sys_exit().
1670                          */
1671                         exit_sem(current);
1672                 }
1673
1674                 if (new_nsproxy) {
1675                         switch_task_namespaces(current, new_nsproxy);
1676                         new_nsproxy = NULL;
1677                 }
1678
1679                 task_lock(current);
1680
1681                 if (new_fs) {
1682                         fs = current->fs;
1683                         spin_lock(&fs->lock);
1684                         current->fs = new_fs;
1685                         if (--fs->users)
1686                                 new_fs = NULL;
1687                         else
1688                                 new_fs = fs;
1689                         spin_unlock(&fs->lock);
1690                 }
1691
1692                 if (new_mm) {
1693                         mm = current->mm;
1694                         active_mm = current->active_mm;
1695                         current->mm = new_mm;
1696                         current->active_mm = new_mm;
1697                         if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
1698                                 atomic_dec(&mm->oom_disable_count);
1699                                 atomic_inc(&new_mm->oom_disable_count);
1700                         }
1701                         activate_mm(active_mm, new_mm);
1702                         new_mm = mm;
1703                 }
1704
1705                 if (new_fd) {
1706                         fd = current->files;
1707                         current->files = new_fd;
1708                         new_fd = fd;
1709                 }
1710
1711                 task_unlock(current);
1712         }
1713
1714         if (new_nsproxy)
1715                 put_nsproxy(new_nsproxy);
1716
1717 bad_unshare_cleanup_fd:
1718         if (new_fd)
1719                 put_files_struct(new_fd);
1720
1721 bad_unshare_cleanup_vm:
1722         if (new_mm)
1723                 mmput(new_mm);
1724
1725 bad_unshare_cleanup_sigh:
1726         if (new_sigh)
1727                 if (atomic_dec_and_test(&new_sigh->count))
1728                         kmem_cache_free(sighand_cachep, new_sigh);
1729
1730 bad_unshare_cleanup_fs:
1731         if (new_fs)
1732                 free_fs_struct(new_fs);
1733
1734 bad_unshare_cleanup_thread:
1735 bad_unshare_out:
1736         return err;
1737 }
1738
1739 /*
1740  *      Helper to unshare the files of the current task.
1741  *      We don't want to expose copy_files internals to
1742  *      the exec layer of the kernel.
1743  */
1744
1745 int unshare_files(struct files_struct **displaced)
1746 {
1747         struct task_struct *task = current;
1748         struct files_struct *copy = NULL;
1749         int error;
1750
1751         error = unshare_fd(CLONE_FILES, &copy);
1752         if (error || !copy) {
1753                 *displaced = NULL;
1754                 return error;
1755         }
1756         *displaced = task->files;
1757         task_lock(task);
1758         task->files = copy;
1759         task_unlock(task);
1760         return 0;
1761 }