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