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/futex.h>
  41 #include <linux/compat.h>
  42 #include <linux/kthread.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/proc_fs.h>
  51 #include <linux/profile.h>
  52 #include <linux/rmap.h>
  53 #include <linux/ksm.h>
  54 #include <linux/acct.h>
  55 #include <linux/tsacct_kern.h>
  56 #include <linux/cn_proc.h>
  57 #include <linux/freezer.h>
  58 #include <linux/delayacct.h>
  59 #include <linux/taskstats_kern.h>
  60 #include <linux/random.h>
  61 #include <linux/tty.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 #include <linux/signalfd.h>
  71
  72 #include <asm/pgtable.h>
  73 #include <asm/pgalloc.h>
  74 #include <asm/uaccess.h>
  75 #include <asm/mmu_context.h>
  76 #include <asm/cacheflush.h>
  77 #include <asm/tlbflush.h>
  78
  79 #include <trace/events/sched.h>
  80
  81 #define CREATE_TRACE_POINTS
  82 #include <trace/events/task.h>
  83
  84 /*
  85  * Protected counters by write_lock_irq(&tasklist_lock)
  86  */
  87 unsigned long total_forks;      /* Handle normal Linux uptimes. */
  88 int nr_threads;                 /* The idle threads do not count.. */
  89
  90 int max_threads;                /* tunable limit on nr_threads */
  91
  92 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
  93
  94 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
  95
  96 #ifdef CONFIG_PROVE_RCU
  97 int lockdep_tasklist_lock_is_held(void)
  98 {
  99         return lockdep_is_held(&tasklist_lock);
 100 }
 101 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
 102 #endif /* #ifdef CONFIG_PROVE_RCU */
 103
 104 int nr_processes(void)
 105 {
 106         int cpu;
 107         int total = 0;
 108
 109         for_each_possible_cpu(cpu)
 110                 total += per_cpu(process_counts, cpu);
 111
 112         return total;
 113 }
 114
 115 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
 116 # define alloc_task_struct_node(node)           \
 117                 kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node)
 118 # define free_task_struct(tsk)                  \
 119                 kmem_cache_free(task_struct_cachep, (tsk))
 120 static struct kmem_cache *task_struct_cachep;
 121 #endif
 122
 123 #ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
 124 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 125                                                   int node)
 126 {
 127 #ifdef CONFIG_DEBUG_STACK_USAGE
 128         gfp_t mask = GFP_KERNEL | __GFP_ZERO;
 129 #else
 130         gfp_t mask = GFP_KERNEL;
 131 #endif
 132         struct page *page = alloc_pages_node(node, mask, THREAD_SIZE_ORDER);
 133
 134         return page ? page_address(page) : NULL;
 135 }
 136
 137 static inline void free_thread_info(struct thread_info *ti)
 138 {
 139         free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 140 }
 141 #endif
 142
 143 /* SLAB cache for signal_struct structures (tsk->signal) */
 144 static struct kmem_cache *signal_cachep;
 145
 146 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 147 struct kmem_cache *sighand_cachep;
 148
 149 /* SLAB cache for files_struct structures (tsk->files) */
 150 struct kmem_cache *files_cachep;
 151
 152 /* SLAB cache for fs_struct structures (tsk->fs) */
 153 struct kmem_cache *fs_cachep;
 154
 155 /* SLAB cache for vm_area_struct structures */
 156 struct kmem_cache *vm_area_cachep;
 157
 158 /* SLAB cache for mm_struct structures (tsk->mm) */
 159 static struct kmem_cache *mm_cachep;
 160
 161 static void account_kernel_stack(struct thread_info *ti, int account)
 162 {
 163         struct zone *zone = page_zone(virt_to_page(ti));
 164
 165         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
 166 }
 167
 168 void free_task(struct task_struct *tsk)
 169 {
 170         account_kernel_stack(tsk->stack, -1);
 171         free_thread_info(tsk->stack);
 172         rt_mutex_debug_task_free(tsk);
 173         ftrace_graph_exit_task(tsk);
 174         free_task_struct(tsk);
 175 }
 176 EXPORT_SYMBOL(free_task);
 177
 178 static inline void free_signal_struct(struct signal_struct *sig)
 179 {
 180         taskstats_tgid_free(sig);
 181         sched_autogroup_exit(sig);
 182         kmem_cache_free(signal_cachep, sig);
 183 }
 184
 185 static inline void put_signal_struct(struct signal_struct *sig)
 186 {
 187         if (atomic_dec_and_test(&sig->sigcnt))
 188                 free_signal_struct(sig);
 189 }
 190
 191 void __put_task_struct(struct task_struct *tsk)
 192 {
 193         WARN_ON(!tsk->exit_state);
 194         WARN_ON(atomic_read(&tsk->usage));
 195         WARN_ON(tsk == current);
 196
 197         security_task_free(tsk);
 198         exit_creds(tsk);
 199         delayacct_tsk_free(tsk);
 200         put_signal_struct(tsk->signal);
 201
 202         if (!profile_handoff_task(tsk))
 203                 free_task(tsk);
 204 }
 205 EXPORT_SYMBOL_GPL(__put_task_struct);
 206
 207 /*
 208  * macro override instead of weak attribute alias, to workaround
 209  * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
 210  */
 211 #ifndef arch_task_cache_init
 212 #define arch_task_cache_init()
 213 #endif
 214
 215 void __init fork_init(unsigned long mempages)
 216 {
 217 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
 218 #ifndef ARCH_MIN_TASKALIGN
 219 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
 220 #endif
 221         /* create a slab on which task_structs can be allocated */
 222         task_struct_cachep =
 223                 kmem_cache_create("task_struct", sizeof(struct task_struct),
 224                         ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
 225 #endif
 226
 227         /* do the arch specific task caches init */
 228         arch_task_cache_init();
 229
 230         /*
 231          * The default maximum number of threads is set to a safe
 232          * value: the thread structures can take up at most half
 233          * of memory.
 234          */
 235         max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
 236
 237         /*
 238          * we need to allow at least 20 threads to boot a system
 239          */
 240         if (max_threads < 20)
 241                 max_threads = 20;
 242
 243         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 244         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
 245         init_task.signal->rlim[RLIMIT_SIGPENDING] =
 246                 init_task.signal->rlim[RLIMIT_NPROC];
 247 }
 248
 249 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
 250                                                struct task_struct *src)
 251 {
 252         *dst = *src;
 253         return 0;
 254 }
 255
 256 static struct task_struct *dup_task_struct(struct task_struct *orig)
 257 {
 258         struct task_struct *tsk;
 259         struct thread_info *ti;
 260         unsigned long *stackend;
 261         int node = tsk_fork_get_node(orig);
 262         int err;
 263
 264         prepare_to_copy(orig);
 265
 266         tsk = alloc_task_struct_node(node);
 267         if (!tsk)
 268                 return NULL;
 269
 270         ti = alloc_thread_info_node(tsk, node);
 271         if (!ti) {
 272                 free_task_struct(tsk);
 273                 return NULL;
 274         }
 275
 276         err = arch_dup_task_struct(tsk, orig);
 277         if (err)
 278                 goto out;
 279
 280         tsk->stack = ti;
 281
 282         setup_thread_stack(tsk, orig);
 283         clear_user_return_notifier(tsk);
 284         clear_tsk_need_resched(tsk);
 285         stackend = end_of_stack(tsk);
 286         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 287
 288 #ifdef CONFIG_CC_STACKPROTECTOR
 289         tsk->stack_canary = get_random_int();
 290 #endif
 291
 292         /*
 293          * One for us, one for whoever does the "release_task()" (usually
 294          * parent)
 295          */
 296         atomic_set(&tsk->usage, 2);
 297 #ifdef CONFIG_BLK_DEV_IO_TRACE
 298         tsk->btrace_seq = 0;
 299 #endif
 300         tsk->splice_pipe = NULL;
 301
 302         account_kernel_stack(ti, 1);
 303
 304         return tsk;
 305
 306 out:
 307         free_thread_info(ti);
 308         free_task_struct(tsk);
 309         return NULL;
 310 }
 311
 312 #ifdef CONFIG_MMU
 313 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 314 {
 315         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 316         struct rb_node **rb_link, *rb_parent;
 317         int retval;
 318         unsigned long charge;
 319         struct mempolicy *pol;
 320
 321         down_write(&oldmm->mmap_sem);
 322         flush_cache_dup_mm(oldmm);
 323         /*
 324          * Not linked in yet - no deadlock potential:
 325          */
 326         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 327
 328         mm->locked_vm = 0;
 329         mm->mmap = NULL;
 330         mm->mmap_cache = NULL;
 331         mm->free_area_cache = oldmm->mmap_base;
 332         mm->cached_hole_size = ~0UL;
 333         mm->map_count = 0;
 334         cpumask_clear(mm_cpumask(mm));
 335         mm->mm_rb = RB_ROOT;
 336         rb_link = &mm->mm_rb.rb_node;
 337         rb_parent = NULL;
 338         pprev = &mm->mmap;
 339         retval = ksm_fork(mm, oldmm);
 340         if (retval)
 341                 goto out;
 342         retval = khugepaged_fork(mm, oldmm);
 343         if (retval)
 344                 goto out;
 345
 346         prev = NULL;
 347         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 348                 struct file *file;
 349
 350                 if (mpnt->vm_flags & VM_DONTCOPY) {
 351                         long pages = vma_pages(mpnt);
 352                         mm->total_vm -= pages;
 353                         vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
 354                                                                 -pages);
 355                         continue;
 356                 }
 357                 charge = 0;
 358                 if (mpnt->vm_flags & VM_ACCOUNT) {
 359                         unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
 360                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
 361                                 goto fail_nomem;
 362                         charge = len;
 363                 }
 364                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 365                 if (!tmp)
 366                         goto fail_nomem;
 367                 *tmp = *mpnt;
 368                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
 369                 pol = mpol_dup(vma_policy(mpnt));
 370                 retval = PTR_ERR(pol);
 371                 if (IS_ERR(pol))
 372                         goto fail_nomem_policy;
 373                 vma_set_policy(tmp, pol);
 374                 tmp->vm_mm = mm;
 375                 if (anon_vma_fork(tmp, mpnt))
 376                         goto fail_nomem_anon_vma_fork;
 377                 tmp->vm_flags &= ~VM_LOCKED;
 378                 tmp->vm_next = tmp->vm_prev = NULL;
 379                 file = tmp->vm_file;
 380                 if (file) {
 381                         struct inode *inode = file->f_path.dentry->d_inode;
 382                         struct address_space *mapping = file->f_mapping;
 383
 384                         get_file(file);
 385                         if (tmp->vm_flags & VM_DENYWRITE)
 386                                 atomic_dec(&inode->i_writecount);
 387                         mutex_lock(&mapping->i_mmap_mutex);
 388                         if (tmp->vm_flags & VM_SHARED)
 389                                 mapping->i_mmap_writable++;
 390                         flush_dcache_mmap_lock(mapping);
 391                         /* insert tmp into the share list, just after mpnt */
 392                         vma_prio_tree_add(tmp, mpnt);
 393                         flush_dcache_mmap_unlock(mapping);
 394                         mutex_unlock(&mapping->i_mmap_mutex);
 395                 }
 396
 397                 /*
 398                  * Clear hugetlb-related page reserves for children. This only
 399                  * affects MAP_PRIVATE mappings. Faults generated by the child
 400                  * are not guaranteed to succeed, even if read-only
 401                  */
 402                 if (is_vm_hugetlb_page(tmp))
 403                         reset_vma_resv_huge_pages(tmp);
 404
 405                 /*
 406                  * Link in the new vma and copy the page table entries.
 407                  */
 408                 *pprev = tmp;
 409                 pprev = &tmp->vm_next;
 410                 tmp->vm_prev = prev;
 411                 prev = tmp;
 412
 413                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 414                 rb_link = &tmp->vm_rb.rb_right;
 415                 rb_parent = &tmp->vm_rb;
 416
 417                 mm->map_count++;
 418                 retval = copy_page_range(mm, oldmm, mpnt);
 419
 420                 if (tmp->vm_ops && tmp->vm_ops->open)
 421                         tmp->vm_ops->open(tmp);
 422
 423                 if (retval)
 424                         goto out;
 425         }
 426         /* a new mm has just been created */
 427         arch_dup_mmap(oldmm, mm);
 428         retval = 0;
 429 out:
 430         up_write(&mm->mmap_sem);
 431         flush_tlb_mm(oldmm);
 432         up_write(&oldmm->mmap_sem);
 433         return retval;
 434 fail_nomem_anon_vma_fork:
 435         mpol_put(pol);
 436 fail_nomem_policy:
 437         kmem_cache_free(vm_area_cachep, tmp);
 438 fail_nomem:
 439         retval = -ENOMEM;
 440         vm_unacct_memory(charge);
 441         goto out;
 442 }
 443
 444 static inline int mm_alloc_pgd(struct mm_struct *mm)
 445 {
 446         mm->pgd = pgd_alloc(mm);
 447         if (unlikely(!mm->pgd))
 448                 return -ENOMEM;
 449         return 0;
 450 }
 451
 452 static inline void mm_free_pgd(struct mm_struct *mm)
 453 {
 454         pgd_free(mm, mm->pgd);
 455 }
 456 #else
 457 #define dup_mmap(mm, oldmm)     (0)
 458 #define mm_alloc_pgd(mm)        (0)
 459 #define mm_free_pgd(mm)
 460 #endif /* CONFIG_MMU */
 461
 462 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 463
 464 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 465 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 466
 467 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 468
 469 static int __init coredump_filter_setup(char *s)
 470 {
 471         default_dump_filter =
 472                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 473                 MMF_DUMP_FILTER_MASK;
 474         return 1;
 475 }
 476
 477 __setup("coredump_filter=", coredump_filter_setup);
 478
 479 #include <linux/init_task.h>
 480
 481 static void mm_init_aio(struct mm_struct *mm)
 482 {
 483 #ifdef CONFIG_AIO
 484         spin_lock_init(&mm->ioctx_lock);
 485         INIT_HLIST_HEAD(&mm->ioctx_list);
 486 #endif
 487 }
 488
 489 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 490 {
 491         atomic_set(&mm->mm_users, 1);
 492         atomic_set(&mm->mm_count, 1);
 493         init_rwsem(&mm->mmap_sem);
 494         INIT_LIST_HEAD(&mm->mmlist);
 495         mm->flags = (current->mm) ?
 496                 (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
 497         mm->core_state = NULL;
 498         mm->nr_ptes = 0;
 499         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 500         spin_lock_init(&mm->page_table_lock);
 501         mm->free_area_cache = TASK_UNMAPPED_BASE;
 502         mm->cached_hole_size = ~0UL;
 503         mm_init_aio(mm);
 504         mm_init_owner(mm, p);
 505
 506         if (likely(!mm_alloc_pgd(mm))) {
 507                 mm->def_flags = 0;
 508                 mmu_notifier_mm_init(mm);
 509                 return mm;
 510         }
 511
 512         free_mm(mm);
 513         return NULL;
 514 }
 515
 516 static void check_mm(struct mm_struct *mm)
 517 {
 518         int i;
 519
 520         for (i = 0; i < NR_MM_COUNTERS; i++) {
 521                 long x = atomic_long_read(&mm->rss_stat.count[i]);
 522
 523                 if (unlikely(x))
 524                         printk(KERN_ALERT "BUG: Bad rss-counter state "
 525                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
 526         }
 527
 528 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 529         VM_BUG_ON(mm->pmd_huge_pte);
 530 #endif
 531 }
 532
 533 /*
 534  * Allocate and initialize an mm_struct.
 535  */
 536 struct mm_struct *mm_alloc(void)
 537 {
 538         struct mm_struct *mm;
 539
 540         mm = allocate_mm();
 541         if (!mm)
 542                 return NULL;
 543
 544         memset(mm, 0, sizeof(*mm));
 545         mm_init_cpumask(mm);
 546         return mm_init(mm, current);
 547 }
 548
 549 /*
 550  * Called when the last reference to the mm
 551  * is dropped: either by a lazy thread or by
 552  * mmput. Free the page directory and the mm.
 553  */
 554 void __mmdrop(struct mm_struct *mm)
 555 {
 556         BUG_ON(mm == &init_mm);
 557         mm_free_pgd(mm);
 558         destroy_context(mm);
 559         mmu_notifier_mm_destroy(mm);
 560         check_mm(mm);
 561         free_mm(mm);
 562 }
 563 EXPORT_SYMBOL_GPL(__mmdrop);
 564
 565 /*
 566  * Decrement the use count and release all resources for an mm.
 567  */
 568 void mmput(struct mm_struct *mm)
 569 {
 570         might_sleep();
 571
 572         if (atomic_dec_and_test(&mm->mm_users)) {
 573                 exit_aio(mm);
 574                 ksm_exit(mm);
 575                 khugepaged_exit(mm); /* must run before exit_mmap */
 576                 exit_mmap(mm);
 577                 set_mm_exe_file(mm, NULL);
 578                 if (!list_empty(&mm->mmlist)) {
 579                         spin_lock(&mmlist_lock);
 580                         list_del(&mm->mmlist);
 581                         spin_unlock(&mmlist_lock);
 582                 }
 583                 put_swap_token(mm);
 584                 if (mm->binfmt)
 585                         module_put(mm->binfmt->module);
 586                 mmdrop(mm);
 587         }
 588 }
 589 EXPORT_SYMBOL_GPL(mmput);
 590
 591 /*
 592  * We added or removed a vma mapping the executable. The vmas are only mapped
 593  * during exec and are not mapped with the mmap system call.
 594  * Callers must hold down_write() on the mm's mmap_sem for these
 595  */
 596 void added_exe_file_vma(struct mm_struct *mm)
 597 {
 598         mm->num_exe_file_vmas++;
 599 }
 600
 601 void removed_exe_file_vma(struct mm_struct *mm)
 602 {
 603         mm->num_exe_file_vmas--;
 604         if ((mm->num_exe_file_vmas == 0) && mm->exe_file) {
 605                 fput(mm->exe_file);
 606                 mm->exe_file = NULL;
 607         }
 608
 609 }
 610
 611 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 612 {
 613         if (new_exe_file)
 614                 get_file(new_exe_file);
 615         if (mm->exe_file)
 616                 fput(mm->exe_file);
 617         mm->exe_file = new_exe_file;
 618         mm->num_exe_file_vmas = 0;
 619 }
 620
 621 struct file *get_mm_exe_file(struct mm_struct *mm)
 622 {
 623         struct file *exe_file;
 624
 625         /* We need mmap_sem to protect against races with removal of
 626          * VM_EXECUTABLE vmas */
 627         down_read(&mm->mmap_sem);
 628         exe_file = mm->exe_file;
 629         if (exe_file)
 630                 get_file(exe_file);
 631         up_read(&mm->mmap_sem);
 632         return exe_file;
 633 }
 634
 635 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
 636 {
 637         /* It's safe to write the exe_file pointer without exe_file_lock because
 638          * this is called during fork when the task is not yet in /proc */
 639         newmm->exe_file = get_mm_exe_file(oldmm);
 640 }
 641
 642 /**
 643  * get_task_mm - acquire a reference to the task's mm
 644  *
 645  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
 646  * this kernel workthread has transiently adopted a user mm with use_mm,
 647  * to do its AIO) is not set and if so returns a reference to it, after
 648  * bumping up the use count.  User must release the mm via mmput()
 649  * after use.  Typically used by /proc and ptrace.
 650  */
 651 struct mm_struct *get_task_mm(struct task_struct *task)
 652 {
 653         struct mm_struct *mm;
 654
 655         task_lock(task);
 656         mm = task->mm;
 657         if (mm) {
 658                 if (task->flags & PF_KTHREAD)
 659                         mm = NULL;
 660                 else
 661                         atomic_inc(&mm->mm_users);
 662         }
 663         task_unlock(task);
 664         return mm;
 665 }
 666 EXPORT_SYMBOL_GPL(get_task_mm);
 667
 668 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 669 {
 670         struct mm_struct *mm;
 671         int err;
 672
 673         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
 674         if (err)
 675                 return ERR_PTR(err);
 676
 677         mm = get_task_mm(task);
 678         if (mm && mm != current->mm &&
 679                         !ptrace_may_access(task, mode)) {
 680                 mmput(mm);
 681                 mm = ERR_PTR(-EACCES);
 682         }
 683         mutex_unlock(&task->signal->cred_guard_mutex);
 684
 685         return mm;
 686 }
 687
 688 static void complete_vfork_done(struct task_struct *tsk)
 689 {
 690         struct completion *vfork;
 691
 692         task_lock(tsk);
 693         vfork = tsk->vfork_done;
 694         if (likely(vfork)) {
 695                 tsk->vfork_done = NULL;
 696                 complete(vfork);
 697         }
 698         task_unlock(tsk);
 699 }
 700
 701 static int wait_for_vfork_done(struct task_struct *child,
 702                                 struct completion *vfork)
 703 {
 704         int killed;
 705
 706         freezer_do_not_count();
 707         killed = wait_for_completion_killable(vfork);
 708         freezer_count();
 709
 710         if (killed) {
 711                 task_lock(child);
 712                 child->vfork_done = NULL;
 713                 task_unlock(child);
 714         }
 715
 716         put_task_struct(child);
 717         return killed;
 718 }
 719
 720 /* Please note the differences between mmput and mm_release.
 721  * mmput is called whenever we stop holding onto a mm_struct,
 722  * error success whatever.
 723  *
 724  * mm_release is called after a mm_struct has been removed
 725  * from the current process.
 726  *
 727  * This difference is important for error handling, when we
 728  * only half set up a mm_struct for a new process and need to restore
 729  * the old one.  Because we mmput the new mm_struct before
 730  * restoring the old one. . .
 731  * Eric Biederman 10 January 1998
 732  */
 733 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 734 {
 735         /* Get rid of any futexes when releasing the mm */
 736 #ifdef CONFIG_FUTEX
 737         if (unlikely(tsk->robust_list)) {
 738                 exit_robust_list(tsk);
 739                 tsk->robust_list = NULL;
 740         }
 741 #ifdef CONFIG_COMPAT
 742         if (unlikely(tsk->compat_robust_list)) {
 743                 compat_exit_robust_list(tsk);
 744                 tsk->compat_robust_list = NULL;
 745         }
 746 #endif
 747         if (unlikely(!list_empty(&tsk->pi_state_list)))
 748                 exit_pi_state_list(tsk);
 749 #endif
 750
 751         /* Get rid of any cached register state */
 752         deactivate_mm(tsk, mm);
 753
 754         if (tsk->vfork_done)
 755                 complete_vfork_done(tsk);
 756
 757         /*
 758          * If we're exiting normally, clear a user-space tid field if
 759          * requested.  We leave this alone when dying by signal, to leave
 760          * the value intact in a core dump, and to save the unnecessary
 761          * trouble, say, a killed vfork parent shouldn't touch this mm.
 762          * Userland only wants this done for a sys_exit.
 763          */
 764         if (tsk->clear_child_tid) {
 765                 if (!(tsk->flags & PF_SIGNALED) &&
 766                     atomic_read(&mm->mm_users) > 1) {
 767                         /*
 768                          * We don't check the error code - if userspace has
 769                          * not set up a proper pointer then tough luck.
 770                          */
 771                         put_user(0, tsk->clear_child_tid);
 772                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
 773                                         1, NULL, NULL, 0);
 774                 }
 775                 tsk->clear_child_tid = NULL;
 776         }
 777 }
 778
 779 /*
 780  * Allocate a new mm structure and copy contents from the
 781  * mm structure of the passed in task structure.
 782  */
 783 struct mm_struct *dup_mm(struct task_struct *tsk)
 784 {
 785         struct mm_struct *mm, *oldmm = current->mm;
 786         int err;
 787
 788         if (!oldmm)
 789                 return NULL;
 790
 791         mm = allocate_mm();
 792         if (!mm)
 793                 goto fail_nomem;
 794
 795         memcpy(mm, oldmm, sizeof(*mm));
 796         mm_init_cpumask(mm);
 797
 798         /* Initializing for Swap token stuff */
 799         mm->token_priority = 0;
 800         mm->last_interval = 0;
 801
 802 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 803         mm->pmd_huge_pte = NULL;
 804 #endif
 805
 806         if (!mm_init(mm, tsk))
 807                 goto fail_nomem;
 808
 809         if (init_new_context(tsk, mm))
 810                 goto fail_nocontext;
 811
 812         dup_mm_exe_file(oldmm, mm);
 813
 814         err = dup_mmap(mm, oldmm);
 815         if (err)
 816                 goto free_pt;
 817
 818         mm->hiwater_rss = get_mm_rss(mm);
 819         mm->hiwater_vm = mm->total_vm;
 820
 821         if (mm->binfmt && !try_module_get(mm->binfmt->module))
 822                 goto free_pt;
 823
 824         return mm;
 825
 826 free_pt:
 827         /* don't put binfmt in mmput, we haven't got module yet */
 828         mm->binfmt = NULL;
 829         mmput(mm);
 830
 831 fail_nomem:
 832         return NULL;
 833
 834 fail_nocontext:
 835         /*
 836          * If init_new_context() failed, we cannot use mmput() to free the mm
 837          * because it calls destroy_context()
 838          */
 839         mm_free_pgd(mm);
 840         free_mm(mm);
 841         return NULL;
 842 }
 843
 844 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 845 {
 846         struct mm_struct *mm, *oldmm;
 847         int retval;
 848
 849         tsk->min_flt = tsk->maj_flt = 0;
 850         tsk->nvcsw = tsk->nivcsw = 0;
 851 #ifdef CONFIG_DETECT_HUNG_TASK
 852         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 853 #endif
 854
 855         tsk->mm = NULL;
 856         tsk->active_mm = NULL;
 857
 858         /*
 859          * Are we cloning a kernel thread?
 860          *
 861          * We need to steal a active VM for that..
 862          */
 863         oldmm = current->mm;
 864         if (!oldmm)
 865                 return 0;
 866
 867         if (clone_flags & CLONE_VM) {
 868                 atomic_inc(&oldmm->mm_users);
 869                 mm = oldmm;
 870                 goto good_mm;
 871         }
 872
 873         retval = -ENOMEM;
 874         mm = dup_mm(tsk);
 875         if (!mm)
 876                 goto fail_nomem;
 877
 878 good_mm:
 879         /* Initializing for Swap token stuff */
 880         mm->token_priority = 0;
 881         mm->last_interval = 0;
 882
 883         tsk->mm = mm;
 884         tsk->active_mm = mm;
 885         return 0;
 886
 887 fail_nomem:
 888         return retval;
 889 }
 890
 891 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 892 {
 893         struct fs_struct *fs = current->fs;
 894         if (clone_flags & CLONE_FS) {
 895                 /* tsk->fs is already what we want */
 896                 spin_lock(&fs->lock);
 897                 if (fs->in_exec) {
 898                         spin_unlock(&fs->lock);
 899                         return -EAGAIN;
 900                 }
 901                 fs->users++;
 902                 spin_unlock(&fs->lock);
 903                 return 0;
 904         }
 905         tsk->fs = copy_fs_struct(fs);
 906         if (!tsk->fs)
 907                 return -ENOMEM;
 908         return 0;
 909 }
 910
 911 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
 912 {
 913         struct files_struct *oldf, *newf;
 914         int error = 0;
 915
 916         /*
 917          * A background process may not have any files ...
 918          */
 919         oldf = current->files;
 920         if (!oldf)
 921                 goto out;
 922
 923         if (clone_flags & CLONE_FILES) {
 924                 atomic_inc(&oldf->count);
 925                 goto out;
 926         }
 927
 928         newf = dup_fd(oldf, &error);
 929         if (!newf)
 930                 goto out;
 931
 932         tsk->files = newf;
 933         error = 0;
 934 out:
 935         return error;
 936 }
 937
 938 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 939 {
 940 #ifdef CONFIG_BLOCK
 941         struct io_context *ioc = current->io_context;
 942         struct io_context *new_ioc;
 943
 944         if (!ioc)
 945                 return 0;
 946         /*
 947          * Share io context with parent, if CLONE_IO is set
 948          */
 949         if (clone_flags & CLONE_IO) {
 950                 tsk->io_context = ioc_task_link(ioc);
 951                 if (unlikely(!tsk->io_context))
 952                         return -ENOMEM;
 953         } else if (ioprio_valid(ioc->ioprio)) {
 954                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
 955                 if (unlikely(!new_ioc))
 956                         return -ENOMEM;
 957
 958                 new_ioc->ioprio = ioc->ioprio;
 959                 put_io_context(new_ioc);
 960         }
 961 #endif
 962         return 0;
 963 }
 964
 965 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 966 {
 967         struct sighand_struct *sig;
 968
 969         if (clone_flags & CLONE_SIGHAND) {
 970                 atomic_inc(&current->sighand->count);
 971                 return 0;
 972         }
 973         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
 974         rcu_assign_pointer(tsk->sighand, sig);
 975         if (!sig)
 976                 return -ENOMEM;
 977         atomic_set(&sig->count, 1);
 978         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
 979         return 0;
 980 }
 981
 982 void __cleanup_sighand(struct sighand_struct *sighand)
 983 {
 984         if (atomic_dec_and_test(&sighand->count)) {
 985                 signalfd_cleanup(sighand);
 986                 kmem_cache_free(sighand_cachep, sighand);
 987         }
 988 }
 989
 990
 991 /*
 992  * Initialize POSIX timer handling for a thread group.
 993  */
 994 static void posix_cpu_timers_init_group(struct signal_struct *sig)
 995 {
 996         unsigned long cpu_limit;
 997
 998         /* Thread group counters. */
 999         thread_group_cputime_init(sig);
1000
1001         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1002         if (cpu_limit != RLIM_INFINITY) {
1003                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1004                 sig->cputimer.running = 1;
1005         }
1006
1007         /* The timer lists. */
1008         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1009         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1010         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1011 }
1012
1013 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1014 {
1015         struct signal_struct *sig;
1016
1017         if (clone_flags & CLONE_THREAD)
1018                 return 0;
1019
1020         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1021         tsk->signal = sig;
1022         if (!sig)
1023                 return -ENOMEM;
1024
1025         sig->nr_threads = 1;
1026         atomic_set(&sig->live, 1);
1027         atomic_set(&sig->sigcnt, 1);
1028         init_waitqueue_head(&sig->wait_chldexit);
1029         if (clone_flags & CLONE_NEWPID)
1030                 sig->flags |= SIGNAL_UNKILLABLE;
1031         sig->curr_target = tsk;
1032         init_sigpending(&sig->shared_pending);
1033         INIT_LIST_HEAD(&sig->posix_timers);
1034
1035         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1036         sig->real_timer.function = it_real_fn;
1037
1038         task_lock(current->group_leader);
1039         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1040         task_unlock(current->group_leader);
1041
1042         posix_cpu_timers_init_group(sig);
1043
1044         tty_audit_fork(sig);
1045         sched_autogroup_fork(sig);
1046
1047 #ifdef CONFIG_CGROUPS
1048         init_rwsem(&sig->group_rwsem);
1049 #endif
1050
1051         sig->oom_adj = current->signal->oom_adj;
1052         sig->oom_score_adj = current->signal->oom_score_adj;
1053         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1054
1055         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1056                                    current->signal->is_child_subreaper;
1057
1058         mutex_init(&sig->cred_guard_mutex);
1059
1060         return 0;
1061 }
1062
1063 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
1064 {
1065         unsigned long new_flags = p->flags;
1066
1067         new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1068         new_flags |= PF_FORKNOEXEC;
1069         p->flags = new_flags;
1070 }
1071
1072 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1073 {
1074         current->clear_child_tid = tidptr;
1075
1076         return task_pid_vnr(current);
1077 }
1078
1079 static void rt_mutex_init_task(struct task_struct *p)
1080 {
1081         raw_spin_lock_init(&p->pi_lock);
1082 #ifdef CONFIG_RT_MUTEXES
1083         plist_head_init(&p->pi_waiters);
1084         p->pi_blocked_on = NULL;
1085 #endif
1086 }
1087
1088 #ifdef CONFIG_MM_OWNER
1089 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1090 {
1091         mm->owner = p;
1092 }
1093 #endif /* CONFIG_MM_OWNER */
1094
1095 /*
1096  * Initialize POSIX timer handling for a single task.
1097  */
1098 static void posix_cpu_timers_init(struct task_struct *tsk)
1099 {
1100         tsk->cputime_expires.prof_exp = 0;
1101         tsk->cputime_expires.virt_exp = 0;
1102         tsk->cputime_expires.sched_exp = 0;
1103         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1104         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1105         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1106 }
1107
1108 /*
1109  * This creates a new process as a copy of the old one,
1110  * but does not actually start it yet.
1111  *
1112  * It copies the registers, and all the appropriate
1113  * parts of the process environment (as per the clone
1114  * flags). The actual kick-off is left to the caller.
1115  */
1116 static struct task_struct *copy_process(unsigned long clone_flags,
1117                                         unsigned long stack_start,
1118                                         struct pt_regs *regs,
1119                                         unsigned long stack_size,
1120                                         int __user *child_tidptr,
1121                                         struct pid *pid,
1122                                         int trace)
1123 {
1124         int retval;
1125         struct task_struct *p;
1126         int cgroup_callbacks_done = 0;
1127
1128         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1129                 return ERR_PTR(-EINVAL);
1130
1131         /*
1132          * Thread groups must share signals as well, and detached threads
1133          * can only be started up within the thread group.
1134          */
1135         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1136                 return ERR_PTR(-EINVAL);
1137
1138         /*
1139          * Shared signal handlers imply shared VM. By way of the above,
1140          * thread groups also imply shared VM. Blocking this case allows
1141          * for various simplifications in other code.
1142          */
1143         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1144                 return ERR_PTR(-EINVAL);
1145
1146         /*
1147          * Siblings of global init remain as zombies on exit since they are
1148          * not reaped by their parent (swapper). To solve this and to avoid
1149          * multi-rooted process trees, prevent global and container-inits
1150          * from creating siblings.
1151          */
1152         if ((clone_flags & CLONE_PARENT) &&
1153                                 current->signal->flags & SIGNAL_UNKILLABLE)
1154                 return ERR_PTR(-EINVAL);
1155
1156         retval = security_task_create(clone_flags);
1157         if (retval)
1158                 goto fork_out;
1159
1160         retval = -ENOMEM;
1161         p = dup_task_struct(current);
1162         if (!p)
1163                 goto fork_out;
1164
1165         ftrace_graph_init_task(p);
1166
1167         rt_mutex_init_task(p);
1168
1169 #ifdef CONFIG_PROVE_LOCKING
1170         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1171         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1172 #endif
1173         retval = -EAGAIN;
1174         if (atomic_read(&p->real_cred->user->processes) >=
1175                         task_rlimit(p, RLIMIT_NPROC)) {
1176                 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1177                     p->real_cred->user != INIT_USER)
1178                         goto bad_fork_free;
1179         }
1180         current->flags &= ~PF_NPROC_EXCEEDED;
1181
1182         retval = copy_creds(p, clone_flags);
1183         if (retval < 0)
1184                 goto bad_fork_free;
1185
1186         /*
1187          * If multiple threads are within copy_process(), then this check
1188          * triggers too late. This doesn't hurt, the check is only there
1189          * to stop root fork bombs.
1190          */
1191         retval = -EAGAIN;
1192         if (nr_threads >= max_threads)
1193                 goto bad_fork_cleanup_count;
1194
1195         if (!try_module_get(task_thread_info(p)->exec_domain->module))
1196                 goto bad_fork_cleanup_count;
1197
1198         p->did_exec = 0;
1199         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1200         copy_flags(clone_flags, p);
1201         INIT_LIST_HEAD(&p->children);
1202         INIT_LIST_HEAD(&p->sibling);
1203         rcu_copy_process(p);
1204         p->vfork_done = NULL;
1205         spin_lock_init(&p->alloc_lock);
1206
1207         init_sigpending(&p->pending);
1208
1209         p->utime = p->stime = p->gtime = 0;
1210         p->utimescaled = p->stimescaled = 0;
1211 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
1212         p->prev_utime = p->prev_stime = 0;
1213 #endif
1214 #if defined(SPLIT_RSS_COUNTING)
1215         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1216 #endif
1217
1218         p->default_timer_slack_ns = current->timer_slack_ns;
1219
1220         task_io_accounting_init(&p->ioac);
1221         acct_clear_integrals(p);
1222
1223         posix_cpu_timers_init(p);
1224
1225         do_posix_clock_monotonic_gettime(&p->start_time);
1226         p->real_start_time = p->start_time;
1227         monotonic_to_bootbased(&p->real_start_time);
1228         p->io_context = NULL;
1229         p->audit_context = NULL;
1230         if (clone_flags & CLONE_THREAD)
1231                 threadgroup_change_begin(current);
1232         cgroup_fork(p);
1233 #ifdef CONFIG_NUMA
1234         p->mempolicy = mpol_dup(p->mempolicy);
1235         if (IS_ERR(p->mempolicy)) {
1236                 retval = PTR_ERR(p->mempolicy);
1237                 p->mempolicy = NULL;
1238                 goto bad_fork_cleanup_cgroup;
1239         }
1240         mpol_fix_fork_child_flag(p);
1241 #endif
1242 #ifdef CONFIG_CPUSETS
1243         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1244         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1245         seqcount_init(&p->mems_allowed_seq);
1246 #endif
1247 #ifdef CONFIG_TRACE_IRQFLAGS
1248         p->irq_events = 0;
1249 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1250         p->hardirqs_enabled = 1;
1251 #else
1252         p->hardirqs_enabled = 0;
1253 #endif
1254         p->hardirq_enable_ip = 0;
1255         p->hardirq_enable_event = 0;
1256         p->hardirq_disable_ip = _THIS_IP_;
1257         p->hardirq_disable_event = 0;
1258         p->softirqs_enabled = 1;
1259         p->softirq_enable_ip = _THIS_IP_;
1260         p->softirq_enable_event = 0;
1261         p->softirq_disable_ip = 0;
1262         p->softirq_disable_event = 0;
1263         p->hardirq_context = 0;
1264         p->softirq_context = 0;
1265 #endif
1266 #ifdef CONFIG_LOCKDEP
1267         p->lockdep_depth = 0; /* no locks held yet */
1268         p->curr_chain_key = 0;
1269         p->lockdep_recursion = 0;
1270 #endif
1271
1272 #ifdef CONFIG_DEBUG_MUTEXES
1273         p->blocked_on = NULL; /* not blocked yet */
1274 #endif
1275 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1276         p->memcg_batch.do_batch = 0;
1277         p->memcg_batch.memcg = NULL;
1278 #endif
1279
1280         /* Perform scheduler related setup. Assign this task to a CPU. */
1281         sched_fork(p);
1282
1283         retval = perf_event_init_task(p);
1284         if (retval)
1285                 goto bad_fork_cleanup_policy;
1286         retval = audit_alloc(p);
1287         if (retval)
1288                 goto bad_fork_cleanup_policy;
1289         /* copy all the process information */
1290         retval = copy_semundo(clone_flags, p);
1291         if (retval)
1292                 goto bad_fork_cleanup_audit;
1293         retval = copy_files(clone_flags, p);
1294         if (retval)
1295                 goto bad_fork_cleanup_semundo;
1296         retval = copy_fs(clone_flags, p);
1297         if (retval)
1298                 goto bad_fork_cleanup_files;
1299         retval = copy_sighand(clone_flags, p);
1300         if (retval)
1301                 goto bad_fork_cleanup_fs;
1302         retval = copy_signal(clone_flags, p);
1303         if (retval)
1304                 goto bad_fork_cleanup_sighand;
1305         retval = copy_mm(clone_flags, p);
1306         if (retval)
1307                 goto bad_fork_cleanup_signal;
1308         retval = copy_namespaces(clone_flags, p);
1309         if (retval)
1310                 goto bad_fork_cleanup_mm;
1311         retval = copy_io(clone_flags, p);
1312         if (retval)
1313                 goto bad_fork_cleanup_namespaces;
1314         retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1315         if (retval)
1316                 goto bad_fork_cleanup_io;
1317
1318         if (pid != &init_struct_pid) {
1319                 retval = -ENOMEM;
1320                 pid = alloc_pid(p->nsproxy->pid_ns);
1321                 if (!pid)
1322                         goto bad_fork_cleanup_io;
1323         }
1324
1325         p->pid = pid_nr(pid);
1326         p->tgid = p->pid;
1327         if (clone_flags & CLONE_THREAD)
1328                 p->tgid = current->tgid;
1329
1330         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1331         /*
1332          * Clear TID on mm_release()?
1333          */
1334         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1335 #ifdef CONFIG_BLOCK
1336         p->plug = NULL;
1337 #endif
1338 #ifdef CONFIG_FUTEX
1339         p->robust_list = NULL;
1340 #ifdef CONFIG_COMPAT
1341         p->compat_robust_list = NULL;
1342 #endif
1343         INIT_LIST_HEAD(&p->pi_state_list);
1344         p->pi_state_cache = NULL;
1345 #endif
1346         /*
1347          * sigaltstack should be cleared when sharing the same VM
1348          */
1349         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1350                 p->sas_ss_sp = p->sas_ss_size = 0;
1351
1352         /*
1353          * Syscall tracing and stepping should be turned off in the
1354          * child regardless of CLONE_PTRACE.
1355          */
1356         user_disable_single_step(p);
1357         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1358 #ifdef TIF_SYSCALL_EMU
1359         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1360 #endif
1361         clear_all_latency_tracing(p);
1362
1363         /* ok, now we should be set up.. */
1364         if (clone_flags & CLONE_THREAD)
1365                 p->exit_signal = -1;
1366         else if (clone_flags & CLONE_PARENT)
1367                 p->exit_signal = current->group_leader->exit_signal;
1368         else
1369                 p->exit_signal = (clone_flags & CSIGNAL);
1370
1371         p->pdeath_signal = 0;
1372         p->exit_state = 0;
1373
1374         p->nr_dirtied = 0;
1375         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1376         p->dirty_paused_when = 0;
1377
1378         /*
1379          * Ok, make it visible to the rest of the system.
1380          * We dont wake it up yet.
1381          */
1382         p->group_leader = p;
1383         INIT_LIST_HEAD(&p->thread_group);
1384
1385         /* Now that the task is set up, run cgroup callbacks if
1386          * necessary. We need to run them before the task is visible
1387          * on the tasklist. */
1388         cgroup_fork_callbacks(p);
1389         cgroup_callbacks_done = 1;
1390
1391         /* Need tasklist lock for parent etc handling! */
1392         write_lock_irq(&tasklist_lock);
1393
1394         /* CLONE_PARENT re-uses the old parent */
1395         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1396                 p->real_parent = current->real_parent;
1397                 p->parent_exec_id = current->parent_exec_id;
1398         } else {
1399                 p->real_parent = current;
1400                 p->parent_exec_id = current->self_exec_id;
1401         }
1402
1403         spin_lock(&current->sighand->siglock);
1404
1405         /*
1406          * Process group and session signals need to be delivered to just the
1407          * parent before the fork or both the parent and the child after the
1408          * fork. Restart if a signal comes in before we add the new process to
1409          * it's process group.
1410          * A fatal signal pending means that current will exit, so the new
1411          * thread can't slip out of an OOM kill (or normal SIGKILL).
1412         */
1413         recalc_sigpending();
1414         if (signal_pending(current)) {
1415                 spin_unlock(&current->sighand->siglock);
1416                 write_unlock_irq(&tasklist_lock);
1417                 retval = -ERESTARTNOINTR;
1418                 goto bad_fork_free_pid;
1419         }
1420
1421         if (clone_flags & CLONE_THREAD) {
1422                 current->signal->nr_threads++;
1423                 atomic_inc(&current->signal->live);
1424                 atomic_inc(&current->signal->sigcnt);
1425                 p->group_leader = current->group_leader;
1426                 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1427         }
1428
1429         if (likely(p->pid)) {
1430                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1431
1432                 if (thread_group_leader(p)) {
1433                         if (is_child_reaper(pid))
1434                                 p->nsproxy->pid_ns->child_reaper = p;
1435
1436                         p->signal->leader_pid = pid;
1437                         p->signal->tty = tty_kref_get(current->signal->tty);
1438                         attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1439                         attach_pid(p, PIDTYPE_SID, task_session(current));
1440                         list_add_tail(&p->sibling, &p->real_parent->children);
1441                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1442                         __this_cpu_inc(process_counts);
1443                 }
1444                 attach_pid(p, PIDTYPE_PID, pid);
1445                 nr_threads++;
1446         }
1447
1448         total_forks++;
1449         spin_unlock(&current->sighand->siglock);
1450         write_unlock_irq(&tasklist_lock);
1451         proc_fork_connector(p);
1452         cgroup_post_fork(p);
1453         if (clone_flags & CLONE_THREAD)
1454                 threadgroup_change_end(current);
1455         perf_event_fork(p);
1456
1457         trace_task_newtask(p, clone_flags);
1458
1459         return p;
1460
1461 bad_fork_free_pid:
1462         if (pid != &init_struct_pid)
1463                 free_pid(pid);
1464 bad_fork_cleanup_io:
1465         if (p->io_context)
1466                 exit_io_context(p);
1467 bad_fork_cleanup_namespaces:
1468         if (unlikely(clone_flags & CLONE_NEWPID))
1469                 pid_ns_release_proc(p->nsproxy->pid_ns);
1470         exit_task_namespaces(p);
1471 bad_fork_cleanup_mm:
1472         if (p->mm)
1473                 mmput(p->mm);
1474 bad_fork_cleanup_signal:
1475         if (!(clone_flags & CLONE_THREAD))
1476                 free_signal_struct(p->signal);
1477 bad_fork_cleanup_sighand:
1478         __cleanup_sighand(p->sighand);
1479 bad_fork_cleanup_fs:
1480         exit_fs(p); /* blocking */
1481 bad_fork_cleanup_files:
1482         exit_files(p); /* blocking */
1483 bad_fork_cleanup_semundo:
1484         exit_sem(p);
1485 bad_fork_cleanup_audit:
1486         audit_free(p);
1487 bad_fork_cleanup_policy:
1488         perf_event_free_task(p);
1489 #ifdef CONFIG_NUMA
1490         mpol_put(p->mempolicy);
1491 bad_fork_cleanup_cgroup:
1492 #endif
1493         if (clone_flags & CLONE_THREAD)
1494                 threadgroup_change_end(current);
1495         cgroup_exit(p, cgroup_callbacks_done);
1496         delayacct_tsk_free(p);
1497         module_put(task_thread_info(p)->exec_domain->module);
1498 bad_fork_cleanup_count:
1499         atomic_dec(&p->cred->user->processes);
1500         exit_creds(p);
1501 bad_fork_free:
1502         free_task(p);
1503 fork_out:
1504         return ERR_PTR(retval);
1505 }
1506
1507 noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1508 {
1509         memset(regs, 0, sizeof(struct pt_regs));
1510         return regs;
1511 }
1512
1513 static inline void init_idle_pids(struct pid_link *links)
1514 {
1515         enum pid_type type;
1516
1517         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1518                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1519                 links[type].pid = &init_struct_pid;
1520         }
1521 }
1522
1523 struct task_struct * __cpuinit fork_idle(int cpu)
1524 {
1525         struct task_struct *task;
1526         struct pt_regs regs;
1527
1528         task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
1529                             &init_struct_pid, 0);
1530         if (!IS_ERR(task)) {
1531                 init_idle_pids(task->pids);
1532                 init_idle(task, cpu);
1533         }
1534
1535         return task;
1536 }
1537
1538 /*
1539  *  Ok, this is the main fork-routine.
1540  *
1541  * It copies the process, and if successful kick-starts
1542  * it and waits for it to finish using the VM if required.
1543  */
1544 long do_fork(unsigned long clone_flags,
1545               unsigned long stack_start,
1546               struct pt_regs *regs,
1547               unsigned long stack_size,
1548               int __user *parent_tidptr,
1549               int __user *child_tidptr)
1550 {
1551         struct task_struct *p;
1552         int trace = 0;
1553         long nr;
1554
1555         /*
1556          * Do some preliminary argument and permissions checking before we
1557          * actually start allocating stuff
1558          */
1559         if (clone_flags & CLONE_NEWUSER) {
1560                 if (clone_flags & CLONE_THREAD)
1561                         return -EINVAL;
1562                 /* hopefully this check will go away when userns support is
1563                  * complete
1564                  */
1565                 if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1566                                 !capable(CAP_SETGID))
1567                         return -EPERM;
1568         }
1569
1570         /*
1571          * Determine whether and which event to report to ptracer.  When
1572          * called from kernel_thread or CLONE_UNTRACED is explicitly
1573          * requested, no event is reported; otherwise, report if the event
1574          * for the type of forking is enabled.
1575          */
1576         if (likely(user_mode(regs)) && !(clone_flags & CLONE_UNTRACED)) {
1577                 if (clone_flags & CLONE_VFORK)
1578                         trace = PTRACE_EVENT_VFORK;
1579                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1580                         trace = PTRACE_EVENT_CLONE;
1581                 else
1582                         trace = PTRACE_EVENT_FORK;
1583
1584                 if (likely(!ptrace_event_enabled(current, trace)))
1585                         trace = 0;
1586         }
1587
1588         p = copy_process(clone_flags, stack_start, regs, stack_size,
1589                          child_tidptr, NULL, trace);
1590         /*
1591          * Do this prior waking up the new thread - the thread pointer
1592          * might get invalid after that point, if the thread exits quickly.
1593          */
1594         if (!IS_ERR(p)) {
1595                 struct completion vfork;
1596
1597                 trace_sched_process_fork(current, p);
1598
1599                 nr = task_pid_vnr(p);
1600
1601                 if (clone_flags & CLONE_PARENT_SETTID)
1602                         put_user(nr, parent_tidptr);
1603
1604                 if (clone_flags & CLONE_VFORK) {
1605                         p->vfork_done = &vfork;
1606                         init_completion(&vfork);
1607                         get_task_struct(p);
1608                 }
1609
1610                 wake_up_new_task(p);
1611
1612                 /* forking complete and child started to run, tell ptracer */
1613                 if (unlikely(trace))
1614                         ptrace_event(trace, nr);
1615
1616                 if (clone_flags & CLONE_VFORK) {
1617                         if (!wait_for_vfork_done(p, &vfork))
1618                                 ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
1619                 }
1620         } else {
1621                 nr = PTR_ERR(p);
1622         }
1623         return nr;
1624 }
1625
1626 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1627 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1628 #endif
1629
1630 static void sighand_ctor(void *data)
1631 {
1632         struct sighand_struct *sighand = data;
1633
1634         spin_lock_init(&sighand->siglock);
1635         init_waitqueue_head(&sighand->signalfd_wqh);
1636 }
1637
1638 void __init proc_caches_init(void)
1639 {
1640         sighand_cachep = kmem_cache_create("sighand_cache",
1641                         sizeof(struct sighand_struct), 0,
1642                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1643                         SLAB_NOTRACK, sighand_ctor);
1644         signal_cachep = kmem_cache_create("signal_cache",
1645                         sizeof(struct signal_struct), 0,
1646                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1647         files_cachep = kmem_cache_create("files_cache",
1648                         sizeof(struct files_struct), 0,
1649                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1650         fs_cachep = kmem_cache_create("fs_cache",
1651                         sizeof(struct fs_struct), 0,
1652                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1653         /*
1654          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1655          * whole struct cpumask for the OFFSTACK case. We could change
1656          * this to *only* allocate as much of it as required by the
1657          * maximum number of CPU's we can ever have.  The cpumask_allocation
1658          * is at the end of the structure, exactly for that reason.
1659          */
1660         mm_cachep = kmem_cache_create("mm_struct",
1661                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1662                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1663         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1664         mmap_init();
1665         nsproxy_cache_init();
1666 }
1667
1668 /*
1669  * Check constraints on flags passed to the unshare system call.
1670  */
1671 static int check_unshare_flags(unsigned long unshare_flags)
1672 {
1673         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1674                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1675                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1676                 return -EINVAL;
1677         /*
1678          * Not implemented, but pretend it works if there is nothing to
1679          * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1680          * needs to unshare vm.
1681          */
1682         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1683                 /* FIXME: get_task_mm() increments ->mm_users */
1684                 if (atomic_read(&current->mm->mm_users) > 1)
1685                         return -EINVAL;
1686         }
1687
1688         return 0;
1689 }
1690
1691 /*
1692  * Unshare the filesystem structure if it is being shared
1693  */
1694 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1695 {
1696         struct fs_struct *fs = current->fs;
1697
1698         if (!(unshare_flags & CLONE_FS) || !fs)
1699                 return 0;
1700
1701         /* don't need lock here; in the worst case we'll do useless copy */
1702         if (fs->users == 1)
1703                 return 0;
1704
1705         *new_fsp = copy_fs_struct(fs);
1706         if (!*new_fsp)
1707                 return -ENOMEM;
1708
1709         return 0;
1710 }
1711
1712 /*
1713  * Unshare file descriptor table if it is being shared
1714  */
1715 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1716 {
1717         struct files_struct *fd = current->files;
1718         int error = 0;
1719
1720         if ((unshare_flags & CLONE_FILES) &&
1721             (fd && atomic_read(&fd->count) > 1)) {
1722                 *new_fdp = dup_fd(fd, &error);
1723                 if (!*new_fdp)
1724                         return error;
1725         }
1726
1727         return 0;
1728 }
1729
1730 /*
1731  * unshare allows a process to 'unshare' part of the process
1732  * context which was originally shared using clone.  copy_*
1733  * functions used by do_fork() cannot be used here directly
1734  * because they modify an inactive task_struct that is being
1735  * constructed. Here we are modifying the current, active,
1736  * task_struct.
1737  */
1738 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1739 {
1740         struct fs_struct *fs, *new_fs = NULL;
1741         struct files_struct *fd, *new_fd = NULL;
1742         struct nsproxy *new_nsproxy = NULL;
1743         int do_sysvsem = 0;
1744         int err;
1745
1746         err = check_unshare_flags(unshare_flags);
1747         if (err)
1748                 goto bad_unshare_out;
1749
1750         /*
1751          * If unsharing namespace, must also unshare filesystem information.
1752          */
1753         if (unshare_flags & CLONE_NEWNS)
1754                 unshare_flags |= CLONE_FS;
1755         /*
1756          * CLONE_NEWIPC must also detach from the undolist: after switching
1757          * to a new ipc namespace, the semaphore arrays from the old
1758          * namespace are unreachable.
1759          */
1760         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1761                 do_sysvsem = 1;
1762         err = unshare_fs(unshare_flags, &new_fs);
1763         if (err)
1764                 goto bad_unshare_out;
1765         err = unshare_fd(unshare_flags, &new_fd);
1766         if (err)
1767                 goto bad_unshare_cleanup_fs;
1768         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy, new_fs);
1769         if (err)
1770                 goto bad_unshare_cleanup_fd;
1771
1772         if (new_fs || new_fd || do_sysvsem || new_nsproxy) {
1773                 if (do_sysvsem) {
1774                         /*
1775                          * CLONE_SYSVSEM is equivalent to sys_exit().
1776                          */
1777                         exit_sem(current);
1778                 }
1779
1780                 if (new_nsproxy) {
1781                         switch_task_namespaces(current, new_nsproxy);
1782                         new_nsproxy = NULL;
1783                 }
1784
1785                 task_lock(current);
1786
1787                 if (new_fs) {
1788                         fs = current->fs;
1789                         spin_lock(&fs->lock);
1790                         current->fs = new_fs;
1791                         if (--fs->users)
1792                                 new_fs = NULL;
1793                         else
1794                                 new_fs = fs;
1795                         spin_unlock(&fs->lock);
1796                 }
1797
1798                 if (new_fd) {
1799                         fd = current->files;
1800                         current->files = new_fd;
1801                         new_fd = fd;
1802                 }
1803
1804                 task_unlock(current);
1805         }
1806
1807         if (new_nsproxy)
1808                 put_nsproxy(new_nsproxy);
1809
1810 bad_unshare_cleanup_fd:
1811         if (new_fd)
1812                 put_files_struct(new_fd);
1813
1814 bad_unshare_cleanup_fs:
1815         if (new_fs)
1816                 free_fs_struct(new_fs);
1817
1818 bad_unshare_out:
1819         return err;
1820 }
1821
1822 /*
1823  *      Helper to unshare the files of the current task.
1824  *      We don't want to expose copy_files internals to
1825  *      the exec layer of the kernel.
1826  */
1827
1828 int unshare_files(struct files_struct **displaced)
1829 {
1830         struct task_struct *task = current;
1831         struct files_struct *copy = NULL;
1832         int error;
1833
1834         error = unshare_fd(CLONE_FILES, &copy);
1835         if (error || !copy) {
1836                 *displaced = NULL;
1837                 return error;
1838         }
1839         *displaced = task->files;
1840         task_lock(task);
1841         task->files = copy;
1842         task_unlock(task);
1843         return 0;
1844 }