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