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