kernel/fork.c

   1 /*
   2  *  linux/kernel/fork.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 /*
   8  *  'fork.c' contains the help-routines for the 'fork' system call
   9  * (see also entry.S and others).
  10  * Fork is rather simple, once you get the hang of it, but the memory
  11  * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
  12  */
  13
  14 #include <linux/slab.h>
  15 #include <linux/init.h>
  16 #include <linux/unistd.h>
  17 #include <linux/module.h>
  18 #include <linux/vmalloc.h>
  19 #include <linux/completion.h>
  20 #include <linux/personality.h>
  21 #include <linux/mempolicy.h>
  22 #include <linux/sem.h>
  23 #include <linux/file.h>
  24 #include <linux/fdtable.h>
  25 #include <linux/iocontext.h>
  26 #include <linux/key.h>
  27 #include <linux/binfmts.h>
  28 #include <linux/mman.h>
  29 #include <linux/mmu_notifier.h>
  30 #include <linux/fs.h>
  31 #include <linux/nsproxy.h>
  32 #include <linux/capability.h>
  33 #include <linux/cpu.h>
  34 #include <linux/cgroup.h>
  35 #include <linux/security.h>
  36 #include <linux/hugetlb.h>
  37 #include <linux/swap.h>
  38 #include <linux/syscalls.h>
  39 #include <linux/jiffies.h>
  40 #include <linux/tracehook.h>
  41 #include <linux/futex.h>
  42 #include <linux/compat.h>
  43 #include <linux/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 #include <linux/signalfd.h>
  71
  72 #include <asm/pgtable.h>
  73 #include <asm/pgalloc.h>
  74 #include <asm/uaccess.h>
  75 #include <asm/mmu_context.h>
  76 #include <asm/cacheflush.h>
  77 #include <asm/tlbflush.h>
  78
  79 #include <trace/events/sched.h>
  80
  81 /*
  82  * Protected counters by write_lock_irq(&tasklist_lock)
  83  */
  84 unsigned long total_forks;      /* Handle normal Linux uptimes. */
  85 int nr_threads;                 /* The idle threads do not count.. */
  86
  87 int max_threads;                /* tunable limit on nr_threads */
  88
  89 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
  90
  91 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
  92
  93 #ifdef CONFIG_PROVE_RCU
  94 int lockdep_tasklist_lock_is_held(void)
  95 {
  96         return lockdep_is_held(&tasklist_lock);
  97 }
  98 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
  99 #endif /* #ifdef CONFIG_PROVE_RCU */
 100
 101 int nr_processes(void)
 102 {
 103         int cpu;
 104         int total = 0;
 105
 106         for_each_possible_cpu(cpu)
 107                 total += per_cpu(process_counts, cpu);
 108
 109         return total;
 110 }
 111
 112 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
 113 # define alloc_task_struct_node(node)           \
 114                 kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node)
 115 # define free_task_struct(tsk)                  \
 116                 kmem_cache_free(task_struct_cachep, (tsk))
 117 static struct kmem_cache *task_struct_cachep;
 118 #endif
 119
 120 #ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
 121 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 122                                                   int node)
 123 {
 124 #ifdef CONFIG_DEBUG_STACK_USAGE
 125         gfp_t mask = GFP_KERNEL | __GFP_ZERO;
 126 #else
 127         gfp_t mask = GFP_KERNEL;
 128 #endif
 129         struct page *page = alloc_pages_node(node, mask, THREAD_SIZE_ORDER);
 130
 131         return page ? page_address(page) : NULL;
 132 }
 133
 134 static inline void free_thread_info(struct thread_info *ti)
 135 {
 136         free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 137 }
 138 #endif
 139
 140 /* SLAB cache for signal_struct structures (tsk->signal) */
 141 static struct kmem_cache *signal_cachep;
 142
 143 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 144 struct kmem_cache *sighand_cachep;
 145
 146 /* SLAB cache for files_struct structures (tsk->files) */
 147 struct kmem_cache *files_cachep;
 148
 149 /* SLAB cache for fs_struct structures (tsk->fs) */
 150 struct kmem_cache *fs_cachep;
 151
 152 /* SLAB cache for vm_area_struct structures */
 153 struct kmem_cache *vm_area_cachep;
 154
 155 /* SLAB cache for mm_struct structures (tsk->mm) */
 156 static struct kmem_cache *mm_cachep;
 157
 158 static void account_kernel_stack(struct thread_info *ti, int account)
 159 {
 160         struct zone *zone = page_zone(virt_to_page(ti));
 161
 162         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
 163 }
 164
 165 void free_task(struct task_struct *tsk)
 166 {
 167         prop_local_destroy_single(&tsk->dirties);
 168         account_kernel_stack(tsk->stack, -1);
 169         free_thread_info(tsk->stack);
 170         rt_mutex_debug_task_free(tsk);
 171         ftrace_graph_exit_task(tsk);
 172         free_task_struct(tsk);
 173 }
 174 EXPORT_SYMBOL(free_task);
 175
 176 static inline void free_signal_struct(struct signal_struct *sig)
 177 {
 178         taskstats_tgid_free(sig);
 179         sched_autogroup_exit(sig);
 180         kmem_cache_free(signal_cachep, sig);
 181 }
 182
 183 static inline void put_signal_struct(struct signal_struct *sig)
 184 {
 185         if (atomic_dec_and_test(&sig->sigcnt))
 186                 free_signal_struct(sig);
 187 }
 188
 189 void __put_task_struct(struct task_struct *tsk)
 190 {
 191         WARN_ON(!tsk->exit_state);
 192         WARN_ON(atomic_read(&tsk->usage));
 193         WARN_ON(tsk == current);
 194
 195         exit_creds(tsk);
 196         delayacct_tsk_free(tsk);
 197         put_signal_struct(tsk->signal);
 198
 199         if (!profile_handoff_task(tsk))
 200                 free_task(tsk);
 201 }
 202 EXPORT_SYMBOL_GPL(__put_task_struct);
 203
 204 /*
 205  * macro override instead of weak attribute alias, to workaround
 206  * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
 207  */
 208 #ifndef arch_task_cache_init
 209 #define arch_task_cache_init()
 210 #endif
 211
 212 void __init fork_init(unsigned long mempages)
 213 {
 214 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
 215 #ifndef ARCH_MIN_TASKALIGN
 216 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
 217 #endif
 218         /* create a slab on which task_structs can be allocated */
 219         task_struct_cachep =
 220                 kmem_cache_create("task_struct", sizeof(struct task_struct),
 221                         ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
 222 #endif
 223
 224         /* do the arch specific task caches init */
 225         arch_task_cache_init();
 226
 227         /*
 228          * The default maximum number of threads is set to a safe
 229          * value: the thread structures can take up at most half
 230          * of memory.
 231          */
 232         max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
 233
 234         /*
 235          * we need to allow at least 20 threads to boot a system
 236          */
 237         if(max_threads < 20)
 238                 max_threads = 20;
 239
 240         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 241         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
 242         init_task.signal->rlim[RLIMIT_SIGPENDING] =
 243                 init_task.signal->rlim[RLIMIT_NPROC];
 244 }
 245
 246 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
 247                                                struct task_struct *src)
 248 {
 249         *dst = *src;
 250         return 0;
 251 }
 252
 253 static struct task_struct *dup_task_struct(struct task_struct *orig)
 254 {
 255         struct task_struct *tsk;
 256         struct thread_info *ti;
 257         unsigned long *stackend;
 258         int node = tsk_fork_get_node(orig);
 259         int err;
 260
 261         prepare_to_copy(orig);
 262
 263         tsk = alloc_task_struct_node(node);
 264         if (!tsk)
 265                 return NULL;
 266
 267         ti = alloc_thread_info_node(tsk, node);
 268         if (!ti) {
 269                 free_task_struct(tsk);
 270                 return NULL;
 271         }
 272
 273         err = arch_dup_task_struct(tsk, orig);
 274         if (err)
 275                 goto out;
 276
 277         tsk->stack = ti;
 278
 279         err = prop_local_init_single(&tsk->dirties);
 280         if (err)
 281                 goto out;
 282
 283         setup_thread_stack(tsk, orig);
 284         clear_user_return_notifier(tsk);
 285         clear_tsk_need_resched(tsk);
 286         stackend = end_of_stack(tsk);
 287         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 288
 289 #ifdef CONFIG_CC_STACKPROTECTOR
 290         tsk->stack_canary = get_random_int();
 291 #endif
 292
 293         /* One for us, one for whoever does the "release_task()" (usually parent) */
 294         atomic_set(&tsk->usage,2);
 295         atomic_set(&tsk->fs_excl, 0);
 296 #ifdef CONFIG_BLK_DEV_IO_TRACE
 297         tsk->btrace_seq = 0;
 298 #endif
 299         tsk->splice_pipe = NULL;
 300
 301         account_kernel_stack(ti, 1);
 302
 303         return tsk;
 304
 305 out:
 306         free_thread_info(ti);
 307         free_task_struct(tsk);
 308         return NULL;
 309 }
 310
 311 #ifdef CONFIG_MMU
 312 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 313 {
 314         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 315         struct rb_node **rb_link, *rb_parent;
 316         int retval;
 317         unsigned long charge;
 318         struct mempolicy *pol;
 319
 320         down_write(&oldmm->mmap_sem);
 321         flush_cache_dup_mm(oldmm);
 322         /*
 323          * Not linked in yet - no deadlock potential:
 324          */
 325         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 326
 327         mm->locked_vm = 0;
 328         mm->mmap = NULL;
 329         mm->mmap_cache = NULL;
 330         mm->free_area_cache = oldmm->mmap_base;
 331         mm->cached_hole_size = ~0UL;
 332         mm->map_count = 0;
 333         cpumask_clear(mm_cpumask(mm));
 334         mm->mm_rb = RB_ROOT;
 335         rb_link = &mm->mm_rb.rb_node;
 336         rb_parent = NULL;
 337         pprev = &mm->mmap;
 338         retval = ksm_fork(mm, oldmm);
 339         if (retval)
 340                 goto out;
 341         retval = khugepaged_fork(mm, oldmm);
 342         if (retval)
 343                 goto out;
 344
 345         prev = NULL;
 346         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 347                 struct file *file;
 348
 349                 if (mpnt->vm_flags & VM_DONTCOPY) {
 350                         long pages = vma_pages(mpnt);
 351                         mm->total_vm -= pages;
 352                         vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
 353                                                                 -pages);
 354                         continue;
 355                 }
 356                 charge = 0;
 357                 if (mpnt->vm_flags & VM_ACCOUNT) {
 358                         unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
 359                         if (security_vm_enough_memory(len))
 360                                 goto fail_nomem;
 361                         charge = len;
 362                 }
 363                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 364                 if (!tmp)
 365                         goto fail_nomem;
 366                 *tmp = *mpnt;
 367                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
 368                 pol = mpol_dup(vma_policy(mpnt));
 369                 retval = PTR_ERR(pol);
 370                 if (IS_ERR(pol))
 371                         goto fail_nomem_policy;
 372                 vma_set_policy(tmp, pol);
 373                 tmp->vm_mm = mm;
 374                 if (anon_vma_fork(tmp, mpnt))
 375                         goto fail_nomem_anon_vma_fork;
 376                 tmp->vm_flags &= ~VM_LOCKED;
 377                 tmp->vm_next = tmp->vm_prev = NULL;
 378                 file = tmp->vm_file;
 379                 if (file) {
 380                         struct inode *inode = file->f_path.dentry->d_inode;
 381                         struct address_space *mapping = file->f_mapping;
 382
 383                         get_file(file);
 384                         if (tmp->vm_flags & VM_DENYWRITE)
 385                                 atomic_dec(&inode->i_writecount);
 386                         mutex_lock(&mapping->i_mmap_mutex);
 387                         if (tmp->vm_flags & VM_SHARED)
 388                                 mapping->i_mmap_writable++;
 389                         flush_dcache_mmap_lock(mapping);
 390                         /* insert tmp into the share list, just after mpnt */
 391                         vma_prio_tree_add(tmp, mpnt);
 392                         flush_dcache_mmap_unlock(mapping);
 393                         mutex_unlock(&mapping->i_mmap_mutex);
 394                 }
 395
 396                 /*
 397                  * Clear hugetlb-related page reserves for children. This only
 398                  * affects MAP_PRIVATE mappings. Faults generated by the child
 399                  * are not guaranteed to succeed, even if read-only
 400                  */
 401                 if (is_vm_hugetlb_page(tmp))
 402                         reset_vma_resv_huge_pages(tmp);
 403
 404                 /*
 405                  * Link in the new vma and copy the page table entries.
 406                  */
 407                 *pprev = tmp;
 408                 pprev = &tmp->vm_next;
 409                 tmp->vm_prev = prev;
 410                 prev = tmp;
 411
 412                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 413                 rb_link = &tmp->vm_rb.rb_right;
 414                 rb_parent = &tmp->vm_rb;
 415
 416                 mm->map_count++;
 417                 retval = copy_page_range(mm, oldmm, mpnt);
 418
 419                 if (tmp->vm_ops && tmp->vm_ops->open)
 420                         tmp->vm_ops->open(tmp);
 421
 422                 if (retval)
 423                         goto out;
 424         }
 425         /* a new mm has just been created */
 426         arch_dup_mmap(oldmm, mm);
 427         retval = 0;
 428 out:
 429         up_write(&mm->mmap_sem);
 430         flush_tlb_mm(oldmm);
 431         up_write(&oldmm->mmap_sem);
 432         return retval;
 433 fail_nomem_anon_vma_fork:
 434         mpol_put(pol);
 435 fail_nomem_policy:
 436         kmem_cache_free(vm_area_cachep, tmp);
 437 fail_nomem:
 438         retval = -ENOMEM;
 439         vm_unacct_memory(charge);
 440         goto out;
 441 }
 442
 443 static inline int mm_alloc_pgd(struct mm_struct * mm)
 444 {
 445         mm->pgd = pgd_alloc(mm);
 446         if (unlikely(!mm->pgd))
 447                 return -ENOMEM;
 448         return 0;
 449 }
 450
 451 static inline void mm_free_pgd(struct mm_struct * mm)
 452 {
 453         pgd_free(mm, mm->pgd);
 454 }
 455 #else
 456 #define dup_mmap(mm, oldmm)     (0)
 457 #define mm_alloc_pgd(mm)        (0)
 458 #define mm_free_pgd(mm)
 459 #endif /* CONFIG_MMU */
 460
 461 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 462
 463 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 464 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 465
 466 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 467
 468 static int __init coredump_filter_setup(char *s)
 469 {
 470         default_dump_filter =
 471                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 472                 MMF_DUMP_FILTER_MASK;
 473         return 1;
 474 }
 475
 476 __setup("coredump_filter=", coredump_filter_setup);
 477
 478 #include <linux/init_task.h>
 479
 480 static void mm_init_aio(struct mm_struct *mm)
 481 {
 482 #ifdef CONFIG_AIO
 483         spin_lock_init(&mm->ioctx_lock);
 484         INIT_HLIST_HEAD(&mm->ioctx_list);
 485 #endif
 486 }
 487
 488 static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
 489 {
 490         atomic_set(&mm->mm_users, 1);
 491         atomic_set(&mm->mm_count, 1);
 492         init_rwsem(&mm->mmap_sem);
 493         INIT_LIST_HEAD(&mm->mmlist);
 494         mm->flags = (current->mm) ?
 495                 (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
 496         mm->core_state = NULL;
 497         mm->nr_ptes = 0;
 498         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 499         spin_lock_init(&mm->page_table_lock);
 500         mm->free_area_cache = TASK_UNMAPPED_BASE;
 501         mm->cached_hole_size = ~0UL;
 502         mm_init_aio(mm);
 503         mm_init_owner(mm, p);
 504         atomic_set(&mm->oom_disable_count, 0);
 505
 506         if (likely(!mm_alloc_pgd(mm))) {
 507                 mm->def_flags = 0;
 508                 mmu_notifier_mm_init(mm);
 509                 return mm;
 510         }
 511
 512         free_mm(mm);
 513         return NULL;
 514 }
 515
 516 /*
 517  * Allocate and initialize an mm_struct.
 518  */
 519 struct mm_struct * mm_alloc(void)
 520 {
 521         struct mm_struct * mm;
 522
 523         mm = allocate_mm();
 524         if (!mm)
 525                 return NULL;
 526
 527         memset(mm, 0, sizeof(*mm));
 528         mm_init_cpumask(mm);
 529         return mm_init(mm, current);
 530 }
 531
 532 /*
 533  * Called when the last reference to the mm
 534  * is dropped: either by a lazy thread or by
 535  * mmput. Free the page directory and the mm.
 536  */
 537 void __mmdrop(struct mm_struct *mm)
 538 {
 539         BUG_ON(mm == &init_mm);
 540         mm_free_pgd(mm);
 541         destroy_context(mm);
 542         mmu_notifier_mm_destroy(mm);
 543 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 544         VM_BUG_ON(mm->pmd_huge_pte);
 545 #endif
 546         free_mm(mm);
 547 }
 548 EXPORT_SYMBOL_GPL(__mmdrop);
 549
 550 /*
 551  * Decrement the use count and release all resources for an mm.
 552  */
 553 void mmput(struct mm_struct *mm)
 554 {
 555         might_sleep();
 556
 557         if (atomic_dec_and_test(&mm->mm_users)) {
 558                 exit_aio(mm);
 559                 ksm_exit(mm);
 560                 khugepaged_exit(mm); /* must run before exit_mmap */
 561                 exit_mmap(mm);
 562                 set_mm_exe_file(mm, NULL);
 563                 if (!list_empty(&mm->mmlist)) {
 564                         spin_lock(&mmlist_lock);
 565                         list_del(&mm->mmlist);
 566                         spin_unlock(&mmlist_lock);
 567                 }
 568                 put_swap_token(mm);
 569                 if (mm->binfmt)
 570                         module_put(mm->binfmt->module);
 571                 mmdrop(mm);
 572         }
 573 }
 574 EXPORT_SYMBOL_GPL(mmput);
 575
 576 /*
 577  * We added or removed a vma mapping the executable. The vmas are only mapped
 578  * during exec and are not mapped with the mmap system call.
 579  * Callers must hold down_write() on the mm's mmap_sem for these
 580  */
 581 void added_exe_file_vma(struct mm_struct *mm)
 582 {
 583         mm->num_exe_file_vmas++;
 584 }
 585
 586 void removed_exe_file_vma(struct mm_struct *mm)
 587 {
 588         mm->num_exe_file_vmas--;
 589         if ((mm->num_exe_file_vmas == 0) && mm->exe_file){
 590                 fput(mm->exe_file);
 591                 mm->exe_file = NULL;
 592         }
 593
 594 }
 595
 596 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 597 {
 598         if (new_exe_file)
 599                 get_file(new_exe_file);
 600         if (mm->exe_file)
 601                 fput(mm->exe_file);
 602         mm->exe_file = new_exe_file;
 603         mm->num_exe_file_vmas = 0;
 604 }
 605
 606 struct file *get_mm_exe_file(struct mm_struct *mm)
 607 {
 608         struct file *exe_file;
 609
 610         /* We need mmap_sem to protect against races with removal of
 611          * VM_EXECUTABLE vmas */
 612         down_read(&mm->mmap_sem);
 613         exe_file = mm->exe_file;
 614         if (exe_file)
 615                 get_file(exe_file);
 616         up_read(&mm->mmap_sem);
 617         return exe_file;
 618 }
 619
 620 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
 621 {
 622         /* It's safe to write the exe_file pointer without exe_file_lock because
 623          * this is called during fork when the task is not yet in /proc */
 624         newmm->exe_file = get_mm_exe_file(oldmm);
 625 }
 626
 627 /**
 628  * get_task_mm - acquire a reference to the task's mm
 629  *
 630  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
 631  * this kernel workthread has transiently adopted a user mm with use_mm,
 632  * to do its AIO) is not set and if so returns a reference to it, after
 633  * bumping up the use count.  User must release the mm via mmput()
 634  * after use.  Typically used by /proc and ptrace.
 635  */
 636 struct mm_struct *get_task_mm(struct task_struct *task)
 637 {
 638         struct mm_struct *mm;
 639
 640         task_lock(task);
 641         mm = task->mm;
 642         if (mm) {
 643                 if (task->flags & PF_KTHREAD)
 644                         mm = NULL;
 645                 else
 646                         atomic_inc(&mm->mm_users);
 647         }
 648         task_unlock(task);
 649         return mm;
 650 }
 651 EXPORT_SYMBOL_GPL(get_task_mm);
 652
 653 /* Please note the differences between mmput and mm_release.
 654  * mmput is called whenever we stop holding onto a mm_struct,
 655  * error success whatever.
 656  *
 657  * mm_release is called after a mm_struct has been removed
 658  * from the current process.
 659  *
 660  * This difference is important for error handling, when we
 661  * only half set up a mm_struct for a new process and need to restore
 662  * the old one.  Because we mmput the new mm_struct before
 663  * restoring the old one. . .
 664  * Eric Biederman 10 January 1998
 665  */
 666 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 667 {
 668         struct completion *vfork_done = tsk->vfork_done;
 669
 670         /* Get rid of any futexes when releasing the mm */
 671 #ifdef CONFIG_FUTEX
 672         if (unlikely(tsk->robust_list)) {
 673                 exit_robust_list(tsk);
 674                 tsk->robust_list = NULL;
 675         }
 676 #ifdef CONFIG_COMPAT
 677         if (unlikely(tsk->compat_robust_list)) {
 678                 compat_exit_robust_list(tsk);
 679                 tsk->compat_robust_list = NULL;
 680         }
 681 #endif
 682         if (unlikely(!list_empty(&tsk->pi_state_list)))
 683                 exit_pi_state_list(tsk);
 684 #endif
 685
 686         /* Get rid of any cached register state */
 687         deactivate_mm(tsk, mm);
 688
 689         /* notify parent sleeping on vfork() */
 690         if (vfork_done) {
 691                 tsk->vfork_done = NULL;
 692                 complete(vfork_done);
 693         }
 694
 695         /*
 696          * If we're exiting normally, clear a user-space tid field if
 697          * requested.  We leave this alone when dying by signal, to leave
 698          * the value intact in a core dump, and to save the unnecessary
 699          * trouble otherwise.  Userland only wants this done for a sys_exit.
 700          */
 701         if (tsk->clear_child_tid) {
 702                 if (!(tsk->flags & PF_SIGNALED) &&
 703                     atomic_read(&mm->mm_users) > 1) {
 704                         /*
 705                          * We don't check the error code - if userspace has
 706                          * not set up a proper pointer then tough luck.
 707                          */
 708                         put_user(0, tsk->clear_child_tid);
 709                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
 710                                         1, NULL, NULL, 0);
 711                 }
 712                 tsk->clear_child_tid = NULL;
 713         }
 714 }
 715
 716 /*
 717  * Allocate a new mm structure and copy contents from the
 718  * mm structure of the passed in task structure.
 719  */
 720 struct mm_struct *dup_mm(struct task_struct *tsk)
 721 {
 722         struct mm_struct *mm, *oldmm = current->mm;
 723         int err;
 724
 725         if (!oldmm)
 726                 return NULL;
 727
 728         mm = allocate_mm();
 729         if (!mm)
 730                 goto fail_nomem;
 731
 732         memcpy(mm, oldmm, sizeof(*mm));
 733         mm_init_cpumask(mm);
 734
 735         /* Initializing for Swap token stuff */
 736         mm->token_priority = 0;
 737         mm->last_interval = 0;
 738
 739 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 740         mm->pmd_huge_pte = NULL;
 741 #endif
 742
 743         if (!mm_init(mm, tsk))
 744                 goto fail_nomem;
 745
 746         if (init_new_context(tsk, mm))
 747                 goto fail_nocontext;
 748
 749         dup_mm_exe_file(oldmm, mm);
 750
 751         err = dup_mmap(mm, oldmm);
 752         if (err)
 753                 goto free_pt;
 754
 755         mm->hiwater_rss = get_mm_rss(mm);
 756         mm->hiwater_vm = mm->total_vm;
 757
 758         if (mm->binfmt && !try_module_get(mm->binfmt->module))
 759                 goto free_pt;
 760
 761         return mm;
 762
 763 free_pt:
 764         /* don't put binfmt in mmput, we haven't got module yet */
 765         mm->binfmt = NULL;
 766         mmput(mm);
 767
 768 fail_nomem:
 769         return NULL;
 770
 771 fail_nocontext:
 772         /*
 773          * If init_new_context() failed, we cannot use mmput() to free the mm
 774          * because it calls destroy_context()
 775          */
 776         mm_free_pgd(mm);
 777         free_mm(mm);
 778         return NULL;
 779 }
 780
 781 static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
 782 {
 783         struct mm_struct * mm, *oldmm;
 784         int retval;
 785
 786         tsk->min_flt = tsk->maj_flt = 0;
 787         tsk->nvcsw = tsk->nivcsw = 0;
 788 #ifdef CONFIG_DETECT_HUNG_TASK
 789         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 790 #endif
 791
 792         tsk->mm = NULL;
 793         tsk->active_mm = NULL;
 794
 795         /*
 796          * Are we cloning a kernel thread?
 797          *
 798          * We need to steal a active VM for that..
 799          */
 800         oldmm = current->mm;
 801         if (!oldmm)
 802                 return 0;
 803
 804         if (clone_flags & CLONE_VM) {
 805                 atomic_inc(&oldmm->mm_users);
 806                 mm = oldmm;
 807                 goto good_mm;
 808         }
 809
 810         retval = -ENOMEM;
 811         mm = dup_mm(tsk);
 812         if (!mm)
 813                 goto fail_nomem;
 814
 815 good_mm:
 816         /* Initializing for Swap token stuff */
 817         mm->token_priority = 0;
 818         mm->last_interval = 0;
 819         if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
 820                 atomic_inc(&mm->oom_disable_count);
 821
 822         tsk->mm = mm;
 823         tsk->active_mm = mm;
 824         return 0;
 825
 826 fail_nomem:
 827         return retval;
 828 }
 829
 830 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 831 {
 832         struct fs_struct *fs = current->fs;
 833         if (clone_flags & CLONE_FS) {
 834                 /* tsk->fs is already what we want */
 835                 spin_lock(&fs->lock);
 836                 if (fs->in_exec) {
 837                         spin_unlock(&fs->lock);
 838                         return -EAGAIN;
 839                 }
 840                 fs->users++;
 841                 spin_unlock(&fs->lock);
 842                 return 0;
 843         }
 844         tsk->fs = copy_fs_struct(fs);
 845         if (!tsk->fs)
 846                 return -ENOMEM;
 847         return 0;
 848 }
 849
 850 static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
 851 {
 852         struct files_struct *oldf, *newf;
 853         int error = 0;
 854
 855         /*
 856          * A background process may not have any files ...
 857          */
 858         oldf = current->files;
 859         if (!oldf)
 860                 goto out;
 861
 862         if (clone_flags & CLONE_FILES) {
 863                 atomic_inc(&oldf->count);
 864                 goto out;
 865         }
 866
 867         newf = dup_fd(oldf, &error);
 868         if (!newf)
 869                 goto out;
 870
 871         tsk->files = newf;
 872         error = 0;
 873 out:
 874         return error;
 875 }
 876
 877 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 878 {
 879 #ifdef CONFIG_BLOCK
 880         struct io_context *ioc = current->io_context;
 881
 882         if (!ioc)
 883                 return 0;
 884         /*
 885          * Share io context with parent, if CLONE_IO is set
 886          */
 887         if (clone_flags & CLONE_IO) {
 888                 tsk->io_context = ioc_task_link(ioc);
 889                 if (unlikely(!tsk->io_context))
 890                         return -ENOMEM;
 891         } else if (ioprio_valid(ioc->ioprio)) {
 892                 tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
 893                 if (unlikely(!tsk->io_context))
 894                         return -ENOMEM;
 895
 896                 tsk->io_context->ioprio = ioc->ioprio;
 897         }
 898 #endif
 899         return 0;
 900 }
 901
 902 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 903 {
 904         struct sighand_struct *sig;
 905
 906         if (clone_flags & CLONE_SIGHAND) {
 907                 atomic_inc(&current->sighand->count);
 908                 return 0;
 909         }
 910         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
 911         rcu_assign_pointer(tsk->sighand, sig);
 912         if (!sig)
 913                 return -ENOMEM;
 914         atomic_set(&sig->count, 1);
 915         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
 916         return 0;
 917 }
 918
 919 void __cleanup_sighand(struct sighand_struct *sighand)
 920 {
 921         if (atomic_dec_and_test(&sighand->count)) {
 922                 signalfd_cleanup(sighand);
 923                 kmem_cache_free(sighand_cachep, sighand);
 924         }
 925 }
 926
 927
 928 /*
 929  * Initialize POSIX timer handling for a thread group.
 930  */
 931 static void posix_cpu_timers_init_group(struct signal_struct *sig)
 932 {
 933         unsigned long cpu_limit;
 934
 935         /* Thread group counters. */
 936         thread_group_cputime_init(sig);
 937
 938         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
 939         if (cpu_limit != RLIM_INFINITY) {
 940                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
 941                 sig->cputimer.running = 1;
 942         }
 943
 944         /* The timer lists. */
 945         INIT_LIST_HEAD(&sig->cpu_timers[0]);
 946         INIT_LIST_HEAD(&sig->cpu_timers[1]);
 947         INIT_LIST_HEAD(&sig->cpu_timers[2]);
 948 }
 949
 950 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 951 {
 952         struct signal_struct *sig;
 953
 954         if (clone_flags & CLONE_THREAD)
 955                 return 0;
 956
 957         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
 958         tsk->signal = sig;
 959         if (!sig)
 960                 return -ENOMEM;
 961
 962         sig->nr_threads = 1;
 963         atomic_set(&sig->live, 1);
 964         atomic_set(&sig->sigcnt, 1);
 965         init_waitqueue_head(&sig->wait_chldexit);
 966         if (clone_flags & CLONE_NEWPID)
 967                 sig->flags |= SIGNAL_UNKILLABLE;
 968         sig->curr_target = tsk;
 969         init_sigpending(&sig->shared_pending);
 970         INIT_LIST_HEAD(&sig->posix_timers);
 971
 972         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 973         sig->real_timer.function = it_real_fn;
 974
 975         task_lock(current->group_leader);
 976         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
 977         task_unlock(current->group_leader);
 978
 979         posix_cpu_timers_init_group(sig);
 980
 981         tty_audit_fork(sig);
 982         sched_autogroup_fork(sig);
 983
 984 #ifdef CONFIG_CGROUPS
 985         init_rwsem(&sig->threadgroup_fork_lock);
 986 #endif
 987
 988         sig->oom_adj = current->signal->oom_adj;
 989         sig->oom_score_adj = current->signal->oom_score_adj;
 990         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
 991
 992         mutex_init(&sig->cred_guard_mutex);
 993
 994         return 0;
 995 }
 996
 997 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
 998 {
 999         unsigned long new_flags = p->flags;
1000
1001         new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1002         new_flags |= PF_FORKNOEXEC;
1003         new_flags |= PF_STARTING;
1004         p->flags = new_flags;
1005         clear_freeze_flag(p);
1006 }
1007
1008 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1009 {
1010         current->clear_child_tid = tidptr;
1011
1012         return task_pid_vnr(current);
1013 }
1014
1015 static void rt_mutex_init_task(struct task_struct *p)
1016 {
1017         raw_spin_lock_init(&p->pi_lock);
1018 #ifdef CONFIG_RT_MUTEXES
1019         plist_head_init_raw(&p->pi_waiters, &p->pi_lock);
1020         p->pi_blocked_on = NULL;
1021 #endif
1022 }
1023
1024 #ifdef CONFIG_MM_OWNER
1025 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1026 {
1027         mm->owner = p;
1028 }
1029 #endif /* CONFIG_MM_OWNER */
1030
1031 /*
1032  * Initialize POSIX timer handling for a single task.
1033  */
1034 static void posix_cpu_timers_init(struct task_struct *tsk)
1035 {
1036         tsk->cputime_expires.prof_exp = cputime_zero;
1037         tsk->cputime_expires.virt_exp = cputime_zero;
1038         tsk->cputime_expires.sched_exp = 0;
1039         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1040         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1041         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1042 }
1043
1044 /*
1045  * This creates a new process as a copy of the old one,
1046  * but does not actually start it yet.
1047  *
1048  * It copies the registers, and all the appropriate
1049  * parts of the process environment (as per the clone
1050  * flags). The actual kick-off is left to the caller.
1051  */
1052 static struct task_struct *copy_process(unsigned long clone_flags,
1053                                         unsigned long stack_start,
1054                                         struct pt_regs *regs,
1055                                         unsigned long stack_size,
1056                                         int __user *child_tidptr,
1057                                         struct pid *pid,
1058                                         int trace)
1059 {
1060         int retval;
1061         struct task_struct *p;
1062         int cgroup_callbacks_done = 0;
1063
1064         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1065                 return ERR_PTR(-EINVAL);
1066
1067         /*
1068          * Thread groups must share signals as well, and detached threads
1069          * can only be started up within the thread group.
1070          */
1071         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1072                 return ERR_PTR(-EINVAL);
1073
1074         /*
1075          * Shared signal handlers imply shared VM. By way of the above,
1076          * thread groups also imply shared VM. Blocking this case allows
1077          * for various simplifications in other code.
1078          */
1079         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1080                 return ERR_PTR(-EINVAL);
1081
1082         /*
1083          * Siblings of global init remain as zombies on exit since they are
1084          * not reaped by their parent (swapper). To solve this and to avoid
1085          * multi-rooted process trees, prevent global and container-inits
1086          * from creating siblings.
1087          */
1088         if ((clone_flags & CLONE_PARENT) &&
1089                                 current->signal->flags & SIGNAL_UNKILLABLE)
1090                 return ERR_PTR(-EINVAL);
1091
1092         retval = security_task_create(clone_flags);
1093         if (retval)
1094                 goto fork_out;
1095
1096         retval = -ENOMEM;
1097         p = dup_task_struct(current);
1098         if (!p)
1099                 goto fork_out;
1100
1101         ftrace_graph_init_task(p);
1102
1103         rt_mutex_init_task(p);
1104
1105 #ifdef CONFIG_PROVE_LOCKING
1106         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1107         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1108 #endif
1109         retval = -EAGAIN;
1110         if (atomic_read(&p->real_cred->user->processes) >=
1111                         task_rlimit(p, RLIMIT_NPROC)) {
1112                 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1113                     p->real_cred->user != INIT_USER)
1114                         goto bad_fork_free;
1115         }
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_TRACE_IRQFLAGS
1182         p->irq_events = 0;
1183 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1184         p->hardirqs_enabled = 1;
1185 #else
1186         p->hardirqs_enabled = 0;
1187 #endif
1188         p->hardirq_enable_ip = 0;
1189         p->hardirq_enable_event = 0;
1190         p->hardirq_disable_ip = _THIS_IP_;
1191         p->hardirq_disable_event = 0;
1192         p->softirqs_enabled = 1;
1193         p->softirq_enable_ip = _THIS_IP_;
1194         p->softirq_enable_event = 0;
1195         p->softirq_disable_ip = 0;
1196         p->softirq_disable_event = 0;
1197         p->hardirq_context = 0;
1198         p->softirq_context = 0;
1199 #endif
1200 #ifdef CONFIG_LOCKDEP
1201         p->lockdep_depth = 0; /* no locks held yet */
1202         p->curr_chain_key = 0;
1203         p->lockdep_recursion = 0;
1204 #endif
1205
1206 #ifdef CONFIG_DEBUG_MUTEXES
1207         p->blocked_on = NULL; /* not blocked yet */
1208 #endif
1209 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1210         p->memcg_batch.do_batch = 0;
1211         p->memcg_batch.memcg = NULL;
1212 #endif
1213
1214         /* Perform scheduler related setup. Assign this task to a CPU. */
1215         sched_fork(p);
1216
1217         retval = perf_event_init_task(p);
1218         if (retval)
1219                 goto bad_fork_cleanup_policy;
1220
1221         if ((retval = audit_alloc(p)))
1222                 goto bad_fork_cleanup_policy;
1223         /* copy all the process information */
1224         if ((retval = copy_semundo(clone_flags, p)))
1225                 goto bad_fork_cleanup_audit;
1226         if ((retval = copy_files(clone_flags, p)))
1227                 goto bad_fork_cleanup_semundo;
1228         if ((retval = copy_fs(clone_flags, p)))
1229                 goto bad_fork_cleanup_files;
1230         if ((retval = copy_sighand(clone_flags, p)))
1231                 goto bad_fork_cleanup_fs;
1232         if ((retval = copy_signal(clone_flags, p)))
1233                 goto bad_fork_cleanup_sighand;
1234         if ((retval = copy_mm(clone_flags, p)))
1235                 goto bad_fork_cleanup_signal;
1236         if ((retval = copy_namespaces(clone_flags, p)))
1237                 goto bad_fork_cleanup_mm;
1238         if ((retval = copy_io(clone_flags, p)))
1239                 goto bad_fork_cleanup_namespaces;
1240         retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1241         if (retval)
1242                 goto bad_fork_cleanup_io;
1243
1244         if (pid != &init_struct_pid) {
1245                 retval = -ENOMEM;
1246                 pid = alloc_pid(p->nsproxy->pid_ns);
1247                 if (!pid)
1248                         goto bad_fork_cleanup_io;
1249         }
1250
1251         p->pid = pid_nr(pid);
1252         p->tgid = p->pid;
1253         if (clone_flags & CLONE_THREAD)
1254                 p->tgid = current->tgid;
1255
1256         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1257         /*
1258          * Clear TID on mm_release()?
1259          */
1260         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1261 #ifdef CONFIG_BLOCK
1262         p->plug = NULL;
1263 #endif
1264 #ifdef CONFIG_FUTEX
1265         p->robust_list = NULL;
1266 #ifdef CONFIG_COMPAT
1267         p->compat_robust_list = NULL;
1268 #endif
1269         INIT_LIST_HEAD(&p->pi_state_list);
1270         p->pi_state_cache = NULL;
1271 #endif
1272         /*
1273          * sigaltstack should be cleared when sharing the same VM
1274          */
1275         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1276                 p->sas_ss_sp = p->sas_ss_size = 0;
1277
1278         /*
1279          * Syscall tracing and stepping should be turned off in the
1280          * child regardless of CLONE_PTRACE.
1281          */
1282         user_disable_single_step(p);
1283         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1284 #ifdef TIF_SYSCALL_EMU
1285         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1286 #endif
1287         clear_all_latency_tracing(p);
1288
1289         /* ok, now we should be set up.. */
1290         p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1291         p->pdeath_signal = 0;
1292         p->exit_state = 0;
1293
1294         /*
1295          * Ok, make it visible to the rest of the system.
1296          * We dont wake it up yet.
1297          */
1298         p->group_leader = p;
1299         INIT_LIST_HEAD(&p->thread_group);
1300
1301         /* Now that the task is set up, run cgroup callbacks if
1302          * necessary. We need to run them before the task is visible
1303          * on the tasklist. */
1304         cgroup_fork_callbacks(p);
1305         cgroup_callbacks_done = 1;
1306
1307         /* Need tasklist lock for parent etc handling! */
1308         write_lock_irq(&tasklist_lock);
1309
1310         /* CLONE_PARENT re-uses the old parent */
1311         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1312                 p->real_parent = current->real_parent;
1313                 p->parent_exec_id = current->parent_exec_id;
1314         } else {
1315                 p->real_parent = current;
1316                 p->parent_exec_id = current->self_exec_id;
1317         }
1318
1319         spin_lock(&current->sighand->siglock);
1320
1321         /*
1322          * Process group and session signals need to be delivered to just the
1323          * parent before the fork or both the parent and the child after the
1324          * fork. Restart if a signal comes in before we add the new process to
1325          * it's process group.
1326          * A fatal signal pending means that current will exit, so the new
1327          * thread can't slip out of an OOM kill (or normal SIGKILL).
1328          */
1329         recalc_sigpending();
1330         if (signal_pending(current)) {
1331                 spin_unlock(&current->sighand->siglock);
1332                 write_unlock_irq(&tasklist_lock);
1333                 retval = -ERESTARTNOINTR;
1334                 goto bad_fork_free_pid;
1335         }
1336
1337         if (clone_flags & CLONE_THREAD) {
1338                 current->signal->nr_threads++;
1339                 atomic_inc(&current->signal->live);
1340                 atomic_inc(&current->signal->sigcnt);
1341                 p->group_leader = current->group_leader;
1342                 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1343         }
1344
1345         if (likely(p->pid)) {
1346                 tracehook_finish_clone(p, clone_flags, trace);
1347
1348                 if (thread_group_leader(p)) {
1349                         if (is_child_reaper(pid))
1350                                 p->nsproxy->pid_ns->child_reaper = p;
1351
1352                         p->signal->leader_pid = pid;
1353                         p->signal->tty = tty_kref_get(current->signal->tty);
1354                         attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1355                         attach_pid(p, PIDTYPE_SID, task_session(current));
1356                         list_add_tail(&p->sibling, &p->real_parent->children);
1357                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1358                         __this_cpu_inc(process_counts);
1359                 }
1360                 attach_pid(p, PIDTYPE_PID, pid);
1361                 nr_threads++;
1362         }
1363
1364         total_forks++;
1365         spin_unlock(&current->sighand->siglock);
1366         write_unlock_irq(&tasklist_lock);
1367         proc_fork_connector(p);
1368         cgroup_post_fork(p);
1369         if (clone_flags & CLONE_THREAD)
1370                 threadgroup_fork_read_unlock(current);
1371         perf_event_fork(p);
1372         return p;
1373
1374 bad_fork_free_pid:
1375         if (pid != &init_struct_pid)
1376                 free_pid(pid);
1377 bad_fork_cleanup_io:
1378         if (p->io_context)
1379                 exit_io_context(p);
1380 bad_fork_cleanup_namespaces:
1381         exit_task_namespaces(p);
1382 bad_fork_cleanup_mm:
1383         if (p->mm) {
1384                 task_lock(p);
1385                 if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
1386                         atomic_dec(&p->mm->oom_disable_count);
1387                 task_unlock(p);
1388                 mmput(p->mm);
1389         }
1390 bad_fork_cleanup_signal:
1391         if (!(clone_flags & CLONE_THREAD))
1392                 free_signal_struct(p->signal);
1393 bad_fork_cleanup_sighand:
1394         __cleanup_sighand(p->sighand);
1395 bad_fork_cleanup_fs:
1396         exit_fs(p); /* blocking */
1397 bad_fork_cleanup_files:
1398         exit_files(p); /* blocking */
1399 bad_fork_cleanup_semundo:
1400         exit_sem(p);
1401 bad_fork_cleanup_audit:
1402         audit_free(p);
1403 bad_fork_cleanup_policy:
1404         perf_event_free_task(p);
1405 #ifdef CONFIG_NUMA
1406         mpol_put(p->mempolicy);
1407 bad_fork_cleanup_cgroup:
1408 #endif
1409         if (clone_flags & CLONE_THREAD)
1410                 threadgroup_fork_read_unlock(current);
1411         cgroup_exit(p, cgroup_callbacks_done);
1412         delayacct_tsk_free(p);
1413         module_put(task_thread_info(p)->exec_domain->module);
1414 bad_fork_cleanup_count:
1415         atomic_dec(&p->cred->user->processes);
1416         exit_creds(p);
1417 bad_fork_free:
1418         free_task(p);
1419 fork_out:
1420         return ERR_PTR(retval);
1421 }
1422
1423 noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1424 {
1425         memset(regs, 0, sizeof(struct pt_regs));
1426         return regs;
1427 }
1428
1429 static inline void init_idle_pids(struct pid_link *links)
1430 {
1431         enum pid_type type;
1432
1433         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1434                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1435                 links[type].pid = &init_struct_pid;
1436         }
1437 }
1438
1439 struct task_struct * __cpuinit fork_idle(int cpu)
1440 {
1441         struct task_struct *task;
1442         struct pt_regs regs;
1443
1444         task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
1445                             &init_struct_pid, 0);
1446         if (!IS_ERR(task)) {
1447                 init_idle_pids(task->pids);
1448                 init_idle(task, cpu);
1449         }
1450
1451         return task;
1452 }
1453
1454 /*
1455  *  Ok, this is the main fork-routine.
1456  *
1457  * It copies the process, and if successful kick-starts
1458  * it and waits for it to finish using the VM if required.
1459  */
1460 long do_fork(unsigned long clone_flags,
1461               unsigned long stack_start,
1462               struct pt_regs *regs,
1463               unsigned long stack_size,
1464               int __user *parent_tidptr,
1465               int __user *child_tidptr)
1466 {
1467         struct task_struct *p;
1468         int trace = 0;
1469         long nr;
1470
1471         /*
1472          * Do some preliminary argument and permissions checking before we
1473          * actually start allocating stuff
1474          */
1475         if (clone_flags & CLONE_NEWUSER) {
1476                 if (clone_flags & CLONE_THREAD)
1477                         return -EINVAL;
1478                 /* hopefully this check will go away when userns support is
1479                  * complete
1480                  */
1481                 if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1482                                 !capable(CAP_SETGID))
1483                         return -EPERM;
1484         }
1485
1486         /*
1487          * When called from kernel_thread, don't do user tracing stuff.
1488          */
1489         if (likely(user_mode(regs)))
1490                 trace = tracehook_prepare_clone(clone_flags);
1491
1492         p = copy_process(clone_flags, stack_start, regs, stack_size,
1493                          child_tidptr, NULL, trace);
1494         /*
1495          * Do this prior waking up the new thread - the thread pointer
1496          * might get invalid after that point, if the thread exits quickly.
1497          */
1498         if (!IS_ERR(p)) {
1499                 struct completion vfork;
1500
1501                 trace_sched_process_fork(current, p);
1502
1503                 nr = task_pid_vnr(p);
1504
1505                 if (clone_flags & CLONE_PARENT_SETTID)
1506                         put_user(nr, parent_tidptr);
1507
1508                 if (clone_flags & CLONE_VFORK) {
1509                         p->vfork_done = &vfork;
1510                         init_completion(&vfork);
1511                 }
1512
1513                 audit_finish_fork(p);
1514                 tracehook_report_clone(regs, clone_flags, nr, p);
1515
1516                 /*
1517                  * We set PF_STARTING at creation in case tracing wants to
1518                  * use this to distinguish a fully live task from one that
1519                  * hasn't gotten to tracehook_report_clone() yet.  Now we
1520                  * clear it and set the child going.
1521                  */
1522                 p->flags &= ~PF_STARTING;
1523
1524                 wake_up_new_task(p);
1525
1526                 tracehook_report_clone_complete(trace, regs,
1527                                                 clone_flags, nr, p);
1528
1529                 if (clone_flags & CLONE_VFORK) {
1530                         freezer_do_not_count();
1531                         wait_for_completion(&vfork);
1532                         freezer_count();
1533                         tracehook_report_vfork_done(p, nr);
1534                 }
1535         } else {
1536                 nr = PTR_ERR(p);
1537         }
1538         return nr;
1539 }
1540
1541 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1542 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1543 #endif
1544
1545 static void sighand_ctor(void *data)
1546 {
1547         struct sighand_struct *sighand = data;
1548
1549         spin_lock_init(&sighand->siglock);
1550         init_waitqueue_head(&sighand->signalfd_wqh);
1551 }
1552
1553 void __init proc_caches_init(void)
1554 {
1555         sighand_cachep = kmem_cache_create("sighand_cache",
1556                         sizeof(struct sighand_struct), 0,
1557                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1558                         SLAB_NOTRACK, sighand_ctor);
1559         signal_cachep = kmem_cache_create("signal_cache",
1560                         sizeof(struct signal_struct), 0,
1561                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1562         files_cachep = kmem_cache_create("files_cache",
1563                         sizeof(struct files_struct), 0,
1564                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1565         fs_cachep = kmem_cache_create("fs_cache",
1566                         sizeof(struct fs_struct), 0,
1567                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1568         /*
1569          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1570          * whole struct cpumask for the OFFSTACK case. We could change
1571          * this to *only* allocate as much of it as required by the
1572          * maximum number of CPU's we can ever have.  The cpumask_allocation
1573          * is at the end of the structure, exactly for that reason.
1574          */
1575         mm_cachep = kmem_cache_create("mm_struct",
1576                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1577                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1578         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1579         mmap_init();
1580 }
1581
1582 /*
1583  * Check constraints on flags passed to the unshare system call.
1584  */
1585 static int check_unshare_flags(unsigned long unshare_flags)
1586 {
1587         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1588                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1589                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1590                 return -EINVAL;
1591         /*
1592          * Not implemented, but pretend it works if there is nothing to
1593          * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1594          * needs to unshare vm.
1595          */
1596         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1597                 /* FIXME: get_task_mm() increments ->mm_users */
1598                 if (atomic_read(&current->mm->mm_users) > 1)
1599                         return -EINVAL;
1600         }
1601
1602         return 0;
1603 }
1604
1605 /*
1606  * Unshare the filesystem structure if it is being shared
1607  */
1608 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1609 {
1610         struct fs_struct *fs = current->fs;
1611
1612         if (!(unshare_flags & CLONE_FS) || !fs)
1613                 return 0;
1614
1615         /* don't need lock here; in the worst case we'll do useless copy */
1616         if (fs->users == 1)
1617                 return 0;
1618
1619         *new_fsp = copy_fs_struct(fs);
1620         if (!*new_fsp)
1621                 return -ENOMEM;
1622
1623         return 0;
1624 }
1625
1626 /*
1627  * Unshare file descriptor table if it is being shared
1628  */
1629 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1630 {
1631         struct files_struct *fd = current->files;
1632         int error = 0;
1633
1634         if ((unshare_flags & CLONE_FILES) &&
1635             (fd && atomic_read(&fd->count) > 1)) {
1636                 *new_fdp = dup_fd(fd, &error);
1637                 if (!*new_fdp)
1638                         return error;
1639         }
1640
1641         return 0;
1642 }
1643
1644 /*
1645  * unshare allows a process to 'unshare' part of the process
1646  * context which was originally shared using clone.  copy_*
1647  * functions used by do_fork() cannot be used here directly
1648  * because they modify an inactive task_struct that is being
1649  * constructed. Here we are modifying the current, active,
1650  * task_struct.
1651  */
1652 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1653 {
1654         struct fs_struct *fs, *new_fs = NULL;
1655         struct files_struct *fd, *new_fd = NULL;
1656         struct nsproxy *new_nsproxy = NULL;
1657         int do_sysvsem = 0;
1658         int err;
1659
1660         err = check_unshare_flags(unshare_flags);
1661         if (err)
1662                 goto bad_unshare_out;
1663
1664         /*
1665          * If unsharing namespace, must also unshare filesystem information.
1666          */
1667         if (unshare_flags & CLONE_NEWNS)
1668                 unshare_flags |= CLONE_FS;
1669         /*
1670          * CLONE_NEWIPC must also detach from the undolist: after switching
1671          * to a new ipc namespace, the semaphore arrays from the old
1672          * namespace are unreachable.
1673          */
1674         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1675                 do_sysvsem = 1;
1676         if ((err = unshare_fs(unshare_flags, &new_fs)))
1677                 goto bad_unshare_out;
1678         if ((err = unshare_fd(unshare_flags, &new_fd)))
1679                 goto bad_unshare_cleanup_fs;
1680         if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1681                         new_fs)))
1682                 goto bad_unshare_cleanup_fd;
1683
1684         if (new_fs || new_fd || do_sysvsem || new_nsproxy) {
1685                 if (do_sysvsem) {
1686                         /*
1687                          * CLONE_SYSVSEM is equivalent to sys_exit().
1688                          */
1689                         exit_sem(current);
1690                 }
1691
1692                 if (new_nsproxy) {
1693                         switch_task_namespaces(current, new_nsproxy);
1694                         new_nsproxy = NULL;
1695                 }
1696
1697                 task_lock(current);
1698
1699                 if (new_fs) {
1700                         fs = current->fs;
1701                         spin_lock(&fs->lock);
1702                         current->fs = new_fs;
1703                         if (--fs->users)
1704                                 new_fs = NULL;
1705                         else
1706                                 new_fs = fs;
1707                         spin_unlock(&fs->lock);
1708                 }
1709
1710                 if (new_fd) {
1711                         fd = current->files;
1712                         current->files = new_fd;
1713                         new_fd = fd;
1714                 }
1715
1716                 task_unlock(current);
1717         }
1718
1719         if (new_nsproxy)
1720                 put_nsproxy(new_nsproxy);
1721
1722 bad_unshare_cleanup_fd:
1723         if (new_fd)
1724                 put_files_struct(new_fd);
1725
1726 bad_unshare_cleanup_fs:
1727         if (new_fs)
1728                 free_fs_struct(new_fs);
1729
1730 bad_unshare_out:
1731         return err;
1732 }
1733
1734 /*
1735  *      Helper to unshare the files of the current task.
1736  *      We don't want to expose copy_files internals to
1737  *      the exec layer of the kernel.
1738  */
1739
1740 int unshare_files(struct files_struct **displaced)
1741 {
1742         struct task_struct *task = current;
1743         struct files_struct *copy = NULL;
1744         int error;
1745
1746         error = unshare_fd(CLONE_FILES, &copy);
1747         if (error || !copy) {
1748                 *displaced = NULL;
1749                 return error;
1750         }
1751         *displaced = task->files;
1752         task_lock(task);
1753         task->files = copy;
1754         task_unlock(task);
1755         return 0;
1756 }