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fork.c

/*
 *  linux/kernel/fork.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 *  'fork.c' contains the help-routines for the 'fork' system call
 * (see also entry.S and others).
 * Fork is rather simple, once you get the hang of it, but the memory
 * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
 */

#include <linux/slab.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#include <linux/completion.h>
#include <linux/mnt_namespace.h>
#include <linux/personality.h>
#include <linux/mempolicy.h>
#include <linux/sem.h>
#include <linux/file.h>
#include <linux/key.h>
#include <linux/binfmts.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/nsproxy.h>
#include <linux/capability.h>
#include <linux/cpu.h>
#include <linux/cgroup.h>
#include <linux/security.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/jiffies.h>
#include <linux/futex.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/rcupdate.h>
#include <linux/ptrace.h>
#include <linux/mount.h>
#include <linux/audit.h>
#include <linux/profile.h>
#include <linux/rmap.h>
#include <linux/acct.h>
#include <linux/tsacct_kern.h>
#include <linux/cn_proc.h>
#include <linux/freezer.h>
#include <linux/delayacct.h>
#include <linux/taskstats_kern.h>
#include <linux/random.h>
#include <linux/tty.h>
#include <linux/proc_fs.h>

#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

/*
 * Protected counters by write_lock_irq(&tasklist_lock)
 */
unsigned long total_forks;    /* Handle normal Linux uptimes. */
int nr_threads;         /* The idle threads do not count.. */

int max_threads;        /* tunable limit on nr_threads */

DEFINE_PER_CPU(unsigned long, process_counts) = 0;

__cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */

int nr_processes(void)
{
      int cpu;
      int total = 0;

      for_each_online_cpu(cpu)
            total += per_cpu(process_counts, cpu);

      return total;
}

#ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
# define alloc_task_struct()  kmem_cache_alloc(task_struct_cachep, GFP_KERNEL)
# define free_task_struct(tsk)      kmem_cache_free(task_struct_cachep, (tsk))
static struct kmem_cache *task_struct_cachep;
#endif

/* SLAB cache for signal_struct structures (tsk->signal) */
static struct kmem_cache *signal_cachep;

/* SLAB cache for sighand_struct structures (tsk->sighand) */
struct kmem_cache *sighand_cachep;

/* SLAB cache for files_struct structures (tsk->files) */
struct kmem_cache *files_cachep;

/* SLAB cache for fs_struct structures (tsk->fs) */
struct kmem_cache *fs_cachep;

/* SLAB cache for vm_area_struct structures */
struct kmem_cache *vm_area_cachep;

/* SLAB cache for mm_struct structures (tsk->mm) */
static struct kmem_cache *mm_cachep;

void free_task(struct task_struct *tsk)
{
      prop_local_destroy_single(&tsk->dirties);
      free_thread_info(tsk->stack);
      rt_mutex_debug_task_free(tsk);
      free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);

void __put_task_struct(struct task_struct *tsk)
{
      WARN_ON(!tsk->exit_state);
      WARN_ON(atomic_read(&tsk->usage));
      WARN_ON(tsk == current);

      security_task_free(tsk);
      free_uid(tsk->user);
      put_group_info(tsk->group_info);
      delayacct_tsk_free(tsk);

      if (!profile_handoff_task(tsk))
            free_task(tsk);
}

void __init fork_init(unsigned long mempages)
{
#ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
#ifndef ARCH_MIN_TASKALIGN
#define ARCH_MIN_TASKALIGN    L1_CACHE_BYTES
#endif
      /* create a slab on which task_structs can be allocated */
      task_struct_cachep =
            kmem_cache_create("task_struct", sizeof(struct task_struct),
                  ARCH_MIN_TASKALIGN, SLAB_PANIC, NULL);
#endif

      /*
       * The default maximum number of threads is set to a safe
       * value: the thread structures can take up at most half
       * of memory.
       */
      max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);

      /*
       * we need to allow at least 20 threads to boot a system
       */
      if(max_threads < 20)
            max_threads = 20;

      init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
      init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
      init_task.signal->rlim[RLIMIT_SIGPENDING] =
            init_task.signal->rlim[RLIMIT_NPROC];
}

static struct task_struct *dup_task_struct(struct task_struct *orig)
{
      struct task_struct *tsk;
      struct thread_info *ti;
      int err;

      prepare_to_copy(orig);

      tsk = alloc_task_struct();
      if (!tsk)
            return NULL;

      ti = alloc_thread_info(tsk);
      if (!ti) {
            free_task_struct(tsk);
            return NULL;
      }

      *tsk = *orig;
      tsk->stack = ti;

      err = prop_local_init_single(&tsk->dirties);
      if (err) {
            free_thread_info(ti);
            free_task_struct(tsk);
            return NULL;
      }

      setup_thread_stack(tsk, orig);

#ifdef CONFIG_CC_STACKPROTECTOR
      tsk->stack_canary = get_random_int();
#endif

      /* One for us, one for whoever does the "release_task()" (usually parent) */
      atomic_set(&tsk->usage,2);
      atomic_set(&tsk->fs_excl, 0);
#ifdef CONFIG_BLK_DEV_IO_TRACE
      tsk->btrace_seq = 0;
#endif
      tsk->splice_pipe = NULL;
      return tsk;
}

#ifdef CONFIG_MMU
static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
{
      struct vm_area_struct *mpnt, *tmp, **pprev;
      struct rb_node **rb_link, *rb_parent;
      int retval;
      unsigned long charge;
      struct mempolicy *pol;

      down_write(&oldmm->mmap_sem);
      flush_cache_dup_mm(oldmm);
      /*
       * Not linked in yet - no deadlock potential:
       */
      down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);

      mm->locked_vm = 0;
      mm->mmap = NULL;
      mm->mmap_cache = NULL;
      mm->free_area_cache = oldmm->mmap_base;
      mm->cached_hole_size = ~0UL;
      mm->map_count = 0;
      cpus_clear(mm->cpu_vm_mask);
      mm->mm_rb = RB_ROOT;
      rb_link = &mm->mm_rb.rb_node;
      rb_parent = NULL;
      pprev = &mm->mmap;

      for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
            struct file *file;

            if (mpnt->vm_flags & VM_DONTCOPY) {
                  long pages = vma_pages(mpnt);
                  mm->total_vm -= pages;
                  vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
                                                -pages);
                  continue;
            }
            charge = 0;
            if (mpnt->vm_flags & VM_ACCOUNT) {
                  unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
                  if (security_vm_enough_memory(len))
                        goto fail_nomem;
                  charge = len;
            }
            tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
            if (!tmp)
                  goto fail_nomem;
            *tmp = *mpnt;
            pol = mpol_copy(vma_policy(mpnt));
            retval = PTR_ERR(pol);
            if (IS_ERR(pol))
                  goto fail_nomem_policy;
            vma_set_policy(tmp, pol);
            tmp->vm_flags &= ~VM_LOCKED;
            tmp->vm_mm = mm;
            tmp->vm_next = NULL;
            anon_vma_link(tmp);
            file = tmp->vm_file;
            if (file) {
                  struct inode *inode = file->f_path.dentry->d_inode;
                  get_file(file);
                  if (tmp->vm_flags & VM_DENYWRITE)
                        atomic_dec(&inode->i_writecount);

                  /* insert tmp into the share list, just after mpnt */
                  spin_lock(&file->f_mapping->i_mmap_lock);
                  tmp->vm_truncate_count = mpnt->vm_truncate_count;
                  flush_dcache_mmap_lock(file->f_mapping);
                  vma_prio_tree_add(tmp, mpnt);
                  flush_dcache_mmap_unlock(file->f_mapping);
                  spin_unlock(&file->f_mapping->i_mmap_lock);
            }

            /*
             * Link in the new vma and copy the page table entries.
             */
            *pprev = tmp;
            pprev = &tmp->vm_next;

            __vma_link_rb(mm, tmp, rb_link, rb_parent);
            rb_link = &tmp->vm_rb.rb_right;
            rb_parent = &tmp->vm_rb;

            mm->map_count++;
            retval = copy_page_range(mm, oldmm, mpnt);

            if (tmp->vm_ops && tmp->vm_ops->open)
                  tmp->vm_ops->open(tmp);

            if (retval)
                  goto out;
      }
      /* a new mm has just been created */
      arch_dup_mmap(oldmm, mm);
      retval = 0;
out:
      up_write(&mm->mmap_sem);
      flush_tlb_mm(oldmm);
      up_write(&oldmm->mmap_sem);
      return retval;
fail_nomem_policy:
      kmem_cache_free(vm_area_cachep, tmp);
fail_nomem:
      retval = -ENOMEM;
      vm_unacct_memory(charge);
      goto out;
}

static inline int mm_alloc_pgd(struct mm_struct * mm)
{
      mm->pgd = pgd_alloc(mm);
      if (unlikely(!mm->pgd))
            return -ENOMEM;
      return 0;
}

static inline void mm_free_pgd(struct mm_struct * mm)
{
      pgd_free(mm->pgd);
}
#else
#define dup_mmap(mm, oldmm)   (0)
#define mm_alloc_pgd(mm)      (0)
#define mm_free_pgd(mm)
#endif /* CONFIG_MMU */

__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);

#define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
#define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))

#include <linux/init_task.h>

static struct mm_struct * mm_init(struct mm_struct * mm)
{
      atomic_set(&mm->mm_users, 1);
      atomic_set(&mm->mm_count, 1);
      init_rwsem(&mm->mmap_sem);
      INIT_LIST_HEAD(&mm->mmlist);
      mm->flags = (current->mm) ? current->mm->flags
                          : MMF_DUMP_FILTER_DEFAULT;
      mm->core_waiters = 0;
      mm->nr_ptes = 0;
      set_mm_counter(mm, file_rss, 0);
      set_mm_counter(mm, anon_rss, 0);
      spin_lock_init(&mm->page_table_lock);
      rwlock_init(&mm->ioctx_list_lock);
      mm->ioctx_list = NULL;
      mm->free_area_cache = TASK_UNMAPPED_BASE;
      mm->cached_hole_size = ~0UL;

      if (likely(!mm_alloc_pgd(mm))) {
            mm->def_flags = 0;
            return mm;
      }
      free_mm(mm);
      return NULL;
}

/*
 * Allocate and initialize an mm_struct.
 */
struct mm_struct * mm_alloc(void)
{
      struct mm_struct * mm;

      mm = allocate_mm();
      if (mm) {
            memset(mm, 0, sizeof(*mm));
            mm = mm_init(mm);
      }
      return mm;
}

/*
 * Called when the last reference to the mm
 * is dropped: either by a lazy thread or by
 * mmput. Free the page directory and the mm.
 */
void fastcall __mmdrop(struct mm_struct *mm)
{
      BUG_ON(mm == &init_mm);
      mm_free_pgd(mm);
      destroy_context(mm);
      free_mm(mm);
}

/*
 * Decrement the use count and release all resources for an mm.
 */
void mmput(struct mm_struct *mm)
{
      might_sleep();

      if (atomic_dec_and_test(&mm->mm_users)) {
            exit_aio(mm);
            exit_mmap(mm);
            if (!list_empty(&mm->mmlist)) {
                  spin_lock(&mmlist_lock);
                  list_del(&mm->mmlist);
                  spin_unlock(&mmlist_lock);
            }
            put_swap_token(mm);
            mmdrop(mm);
      }
}
EXPORT_SYMBOL_GPL(mmput);

/**
 * get_task_mm - acquire a reference to the task's mm
 *
 * Returns %NULL if the task has no mm.  Checks PF_BORROWED_MM (meaning
 * this kernel workthread has transiently adopted a user mm with use_mm,
 * to do its AIO) is not set and if so returns a reference to it, after
 * bumping up the use count.  User must release the mm via mmput()
 * after use.  Typically used by /proc and ptrace.
 */
struct mm_struct *get_task_mm(struct task_struct *task)
{
      struct mm_struct *mm;

      task_lock(task);
      mm = task->mm;
      if (mm) {
            if (task->flags & PF_BORROWED_MM)
                  mm = NULL;
            else
                  atomic_inc(&mm->mm_users);
      }
      task_unlock(task);
      return mm;
}
EXPORT_SYMBOL_GPL(get_task_mm);

/* Please note the differences between mmput and mm_release.
 * mmput is called whenever we stop holding onto a mm_struct,
 * error success whatever.
 *
 * mm_release is called after a mm_struct has been removed
 * from the current process.
 *
 * This difference is important for error handling, when we
 * only half set up a mm_struct for a new process and need to restore
 * the old one.  Because we mmput the new mm_struct before
 * restoring the old one. . .
 * Eric Biederman 10 January 1998
 */
void mm_release(struct task_struct *tsk, struct mm_struct *mm)
{
      struct completion *vfork_done = tsk->vfork_done;

      /* Get rid of any cached register state */
      deactivate_mm(tsk, mm);

      /* notify parent sleeping on vfork() */
      if (vfork_done) {
            tsk->vfork_done = NULL;
            complete(vfork_done);
      }

      /*
       * If we're exiting normally, clear a user-space tid field if
       * requested.  We leave this alone when dying by signal, to leave
       * the value intact in a core dump, and to save the unnecessary
       * trouble otherwise.  Userland only wants this done for a sys_exit.
       */
      if (tsk->clear_child_tid
          && !(tsk->flags & PF_SIGNALED)
          && atomic_read(&mm->mm_users) > 1) {
            u32 __user * tidptr = tsk->clear_child_tid;
            tsk->clear_child_tid = NULL;

            /*
             * We don't check the error code - if userspace has
             * not set up a proper pointer then tough luck.
             */
            put_user(0, tidptr);
            sys_futex(tidptr, FUTEX_WAKE, 1, NULL, NULL, 0);
      }
}

/*
 * Allocate a new mm structure and copy contents from the
 * mm structure of the passed in task structure.
 */
static struct mm_struct *dup_mm(struct task_struct *tsk)
{
      struct mm_struct *mm, *oldmm = current->mm;
      int err;

      if (!oldmm)
            return NULL;

      mm = allocate_mm();
      if (!mm)
            goto fail_nomem;

      memcpy(mm, oldmm, sizeof(*mm));

      /* Initializing for Swap token stuff */
      mm->token_priority = 0;
      mm->last_interval = 0;

      if (!mm_init(mm))
            goto fail_nomem;

      if (init_new_context(tsk, mm))
            goto fail_nocontext;

      err = dup_mmap(mm, oldmm);
      if (err)
            goto free_pt;

      mm->hiwater_rss = get_mm_rss(mm);
      mm->hiwater_vm = mm->total_vm;

      return mm;

free_pt:
      mmput(mm);

fail_nomem:
      return NULL;

fail_nocontext:
      /*
       * If init_new_context() failed, we cannot use mmput() to free the mm
       * because it calls destroy_context()
       */
      mm_free_pgd(mm);
      free_mm(mm);
      return NULL;
}

static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
      struct mm_struct * mm, *oldmm;
      int retval;

      tsk->min_flt = tsk->maj_flt = 0;
      tsk->nvcsw = tsk->nivcsw = 0;

      tsk->mm = NULL;
      tsk->active_mm = NULL;

      /*
       * Are we cloning a kernel thread?
       *
       * We need to steal a active VM for that..
       */
      oldmm = current->mm;
      if (!oldmm)
            return 0;

      if (clone_flags & CLONE_VM) {
            atomic_inc(&oldmm->mm_users);
            mm = oldmm;
            goto good_mm;
      }

      retval = -ENOMEM;
      mm = dup_mm(tsk);
      if (!mm)
            goto fail_nomem;

good_mm:
      /* Initializing for Swap token stuff */
      mm->token_priority = 0;
      mm->last_interval = 0;

      tsk->mm = mm;
      tsk->active_mm = mm;
      return 0;

fail_nomem:
      return retval;
}

static struct fs_struct *__copy_fs_struct(struct fs_struct *old)
{
      struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
      /* We don't need to lock fs - think why ;-) */
      if (fs) {
            atomic_set(&fs->count, 1);
            rwlock_init(&fs->lock);
            fs->umask = old->umask;
            read_lock(&old->lock);
            fs->rootmnt = mntget(old->rootmnt);
            fs->root = dget(old->root);
            fs->pwdmnt = mntget(old->pwdmnt);
            fs->pwd = dget(old->pwd);
            if (old->altroot) {
                  fs->altrootmnt = mntget(old->altrootmnt);
                  fs->altroot = dget(old->altroot);
            } else {
                  fs->altrootmnt = NULL;
                  fs->altroot = NULL;
            }
            read_unlock(&old->lock);
      }
      return fs;
}

struct fs_struct *copy_fs_struct(struct fs_struct *old)
{
      return __copy_fs_struct(old);
}

EXPORT_SYMBOL_GPL(copy_fs_struct);

static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
{
      if (clone_flags & CLONE_FS) {
            atomic_inc(&current->fs->count);
            return 0;
      }
      tsk->fs = __copy_fs_struct(current->fs);
      if (!tsk->fs)
            return -ENOMEM;
      return 0;
}

static int count_open_files(struct fdtable *fdt)
{
      int size = fdt->max_fds;
      int i;

      /* Find the last open fd */
      for (i = size/(8*sizeof(long)); i > 0; ) {
            if (fdt->open_fds->fds_bits[--i])
                  break;
      }
      i = (i+1) * 8 * sizeof(long);
      return i;
}

static struct files_struct *alloc_files(void)
{
      struct files_struct *newf;
      struct fdtable *fdt;

      newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
      if (!newf)
            goto out;

      atomic_set(&newf->count, 1);

      spin_lock_init(&newf->file_lock);
      newf->next_fd = 0;
      fdt = &newf->fdtab;
      fdt->max_fds = NR_OPEN_DEFAULT;
      fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
      fdt->open_fds = (fd_set *)&newf->open_fds_init;
      fdt->fd = &newf->fd_array[0];
      INIT_RCU_HEAD(&fdt->rcu);
      fdt->next = NULL;
      rcu_assign_pointer(newf->fdt, fdt);
out:
      return newf;
}

/*
 * Allocate a new files structure and copy contents from the
 * passed in files structure.
 * errorp will be valid only when the returned files_struct is NULL.
 */
static struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
{
      struct files_struct *newf;
      struct file **old_fds, **new_fds;
      int open_files, size, i;
      struct fdtable *old_fdt, *new_fdt;

      *errorp = -ENOMEM;
      newf = alloc_files();
      if (!newf)
            goto out;

      spin_lock(&oldf->file_lock);
      old_fdt = files_fdtable(oldf);
      new_fdt = files_fdtable(newf);
      open_files = count_open_files(old_fdt);

      /*
       * Check whether we need to allocate a larger fd array and fd set.
       * Note: we're not a clone task, so the open count won't change.
       */
      if (open_files > new_fdt->max_fds) {
            new_fdt->max_fds = 0;
            spin_unlock(&oldf->file_lock);
            spin_lock(&newf->file_lock);
            *errorp = expand_files(newf, open_files-1);
            spin_unlock(&newf->file_lock);
            if (*errorp < 0)
                  goto out_release;
            new_fdt = files_fdtable(newf);
            /*
             * Reacquire the oldf lock and a pointer to its fd table
             * who knows it may have a new bigger fd table. We need
             * the latest pointer.
             */
            spin_lock(&oldf->file_lock);
            old_fdt = files_fdtable(oldf);
      }

      old_fds = old_fdt->fd;
      new_fds = new_fdt->fd;

      memcpy(new_fdt->open_fds->fds_bits,
            old_fdt->open_fds->fds_bits, open_files/8);
      memcpy(new_fdt->close_on_exec->fds_bits,
            old_fdt->close_on_exec->fds_bits, open_files/8);

      for (i = open_files; i != 0; i--) {
            struct file *f = *old_fds++;
            if (f) {
                  get_file(f);
            } else {
                  /*
                   * The fd may be claimed in the fd bitmap but not yet
                   * instantiated in the files array if a sibling thread
                   * is partway through open().  So make sure that this
                   * fd is available to the new process.
                   */
                  FD_CLR(open_files - i, new_fdt->open_fds);
            }
            rcu_assign_pointer(*new_fds++, f);
      }
      spin_unlock(&oldf->file_lock);

      /* compute the remainder to be cleared */
      size = (new_fdt->max_fds - open_files) * sizeof(struct file *);

      /* This is long word aligned thus could use a optimized version */
      memset(new_fds, 0, size);

      if (new_fdt->max_fds > open_files) {
            int left = (new_fdt->max_fds-open_files)/8;
            int start = open_files / (8 * sizeof(unsigned long));

            memset(&new_fdt->open_fds->fds_bits[start], 0, left);
            memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
      }

      return newf;

out_release:
      kmem_cache_free(files_cachep, newf);
out:
      return NULL;
}

static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
      struct files_struct *oldf, *newf;
      int error = 0;

      /*
       * A background process may not have any files ...
       */
      oldf = current->files;
      if (!oldf)
            goto out;

      if (clone_flags & CLONE_FILES) {
            atomic_inc(&oldf->count);
            goto out;
      }

      /*
       * Note: we may be using current for both targets (See exec.c)
       * This works because we cache current->files (old) as oldf. Don't
       * break this.
       */
      tsk->files = NULL;
      newf = dup_fd(oldf, &error);
      if (!newf)
            goto out;

      tsk->files = newf;
      error = 0;
out:
      return error;
}

/*
 *    Helper to unshare the files of the current task.
 *    We don't want to expose copy_files internals to
 *    the exec layer of the kernel.
 */

int unshare_files(void)
{
      struct files_struct *files  = current->files;
      int rc;

      BUG_ON(!files);

      /* This can race but the race causes us to copy when we don't
         need to and drop the copy */
      if(atomic_read(&files->count) == 1)
      {
            atomic_inc(&files->count);
            return 0;
      }
      rc = copy_files(0, current);
      if(rc)
            current->files = files;
      return rc;
}

EXPORT_SYMBOL(unshare_files);

static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
{
      struct sighand_struct *sig;

      if (clone_flags & (CLONE_SIGHAND | CLONE_THREAD)) {
            atomic_inc(&current->sighand->count);
            return 0;
      }
      sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
      rcu_assign_pointer(tsk->sighand, sig);
      if (!sig)
            return -ENOMEM;
      atomic_set(&sig->count, 1);
      memcpy(sig->action, current->sighand->action, sizeof(sig->action));
      return 0;
}

void __cleanup_sighand(struct sighand_struct *sighand)
{
      if (atomic_dec_and_test(&sighand->count))
            kmem_cache_free(sighand_cachep, sighand);
}

static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
{
      struct signal_struct *sig;
      int ret;

      if (clone_flags & CLONE_THREAD) {
            atomic_inc(&current->signal->count);
            atomic_inc(&current->signal->live);
            return 0;
      }
      sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
      tsk->signal = sig;
      if (!sig)
            return -ENOMEM;

      ret = copy_thread_group_keys(tsk);
      if (ret < 0) {
            kmem_cache_free(signal_cachep, sig);
            return ret;
      }

      atomic_set(&sig->count, 1);
      atomic_set(&sig->live, 1);
      init_waitqueue_head(&sig->wait_chldexit);
      sig->flags = 0;
      sig->group_exit_code = 0;
      sig->group_exit_task = NULL;
      sig->group_stop_count = 0;
      sig->curr_target = NULL;
      init_sigpending(&sig->shared_pending);
      INIT_LIST_HEAD(&sig->posix_timers);

      hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
      sig->it_real_incr.tv64 = 0;
      sig->real_timer.function = it_real_fn;
      sig->tsk = tsk;

      sig->it_virt_expires = cputime_zero;
      sig->it_virt_incr = cputime_zero;
      sig->it_prof_expires = cputime_zero;
      sig->it_prof_incr = cputime_zero;

      sig->leader = 0;  /* session leadership doesn't inherit */
      sig->tty_old_pgrp = NULL;

      sig->utime = sig->stime = sig->cutime = sig->cstime = cputime_zero;
      sig->gtime = cputime_zero;
      sig->cgtime = cputime_zero;
      sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
      sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
      sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
      sig->sum_sched_runtime = 0;
      INIT_LIST_HEAD(&sig->cpu_timers[0]);
      INIT_LIST_HEAD(&sig->cpu_timers[1]);
      INIT_LIST_HEAD(&sig->cpu_timers[2]);
      taskstats_tgid_init(sig);

      task_lock(current->group_leader);
      memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
      task_unlock(current->group_leader);

      if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
            /*
             * New sole thread in the process gets an expiry time
             * of the whole CPU time limit.
             */
            tsk->it_prof_expires =
                  secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
      }
      acct_init_pacct(&sig->pacct);

      tty_audit_fork(sig);

      return 0;
}

void __cleanup_signal(struct signal_struct *sig)
{
      exit_thread_group_keys(sig);
      kmem_cache_free(signal_cachep, sig);
}

static void cleanup_signal(struct task_struct *tsk)
{
      struct signal_struct *sig = tsk->signal;

      atomic_dec(&sig->live);

      if (atomic_dec_and_test(&sig->count))
            __cleanup_signal(sig);
}

static void copy_flags(unsigned long clone_flags, struct task_struct *p)
{
      unsigned long new_flags = p->flags;

      new_flags &= ~PF_SUPERPRIV;
      new_flags |= PF_FORKNOEXEC;
      if (!(clone_flags & CLONE_PTRACE))
            p->ptrace = 0;
      p->flags = new_flags;
      clear_freeze_flag(p);
}

asmlinkage long sys_set_tid_address(int __user *tidptr)
{
      current->clear_child_tid = tidptr;

      return task_pid_vnr(current);
}

static void rt_mutex_init_task(struct task_struct *p)
{
      spin_lock_init(&p->pi_lock);
#ifdef CONFIG_RT_MUTEXES
      plist_head_init(&p->pi_waiters, &p->pi_lock);
      p->pi_blocked_on = NULL;
#endif
}

/*
 * This creates a new process as a copy of the old one,
 * but does not actually start it yet.
 *
 * It copies the registers, and all the appropriate
 * parts of the process environment (as per the clone
 * flags). The actual kick-off is left to the caller.
 */
static struct task_struct *copy_process(unsigned long clone_flags,
                              unsigned long stack_start,
                              struct pt_regs *regs,
                              unsigned long stack_size,
                              int __user *child_tidptr,
                              struct pid *pid)
{
      int retval;
      struct task_struct *p;
      int cgroup_callbacks_done = 0;

      if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
            return ERR_PTR(-EINVAL);

      /*
       * Thread groups must share signals as well, and detached threads
       * can only be started up within the thread group.
       */
      if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
            return ERR_PTR(-EINVAL);

      /*
       * Shared signal handlers imply shared VM. By way of the above,
       * thread groups also imply shared VM. Blocking this case allows
       * for various simplifications in other code.
       */
      if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
            return ERR_PTR(-EINVAL);

      retval = security_task_create(clone_flags);
      if (retval)
            goto fork_out;

      retval = -ENOMEM;
      p = dup_task_struct(current);
      if (!p)
            goto fork_out;

      rt_mutex_init_task(p);

#ifdef CONFIG_TRACE_IRQFLAGS
      DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
      DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
#endif
      retval = -EAGAIN;
      if (atomic_read(&p->user->processes) >=
                  p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
            if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
                p->user != current->nsproxy->user_ns->root_user)
                  goto bad_fork_free;
      }

      atomic_inc(&p->user->__count);
      atomic_inc(&p->user->processes);
      get_group_info(p->group_info);

      /*
       * If multiple threads are within copy_process(), then this check
       * triggers too late. This doesn't hurt, the check is only there
       * to stop root fork bombs.
       */
      if (nr_threads >= max_threads)
            goto bad_fork_cleanup_count;

      if (!try_module_get(task_thread_info(p)->exec_domain->module))
            goto bad_fork_cleanup_count;

      if (p->binfmt && !try_module_get(p->binfmt->module))
            goto bad_fork_cleanup_put_domain;

      p->did_exec = 0;
      delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
      copy_flags(clone_flags, p);
      INIT_LIST_HEAD(&p->children);
      INIT_LIST_HEAD(&p->sibling);
      p->vfork_done = NULL;
      spin_lock_init(&p->alloc_lock);

      clear_tsk_thread_flag(p, TIF_SIGPENDING);
      init_sigpending(&p->pending);

      p->utime = cputime_zero;
      p->stime = cputime_zero;
      p->gtime = cputime_zero;
      p->utimescaled = cputime_zero;
      p->stimescaled = cputime_zero;
      p->prev_utime = cputime_zero;
      p->prev_stime = cputime_zero;

#ifdef CONFIG_TASK_XACCT
      p->rchar = 0;           /* I/O counter: bytes read */
      p->wchar = 0;           /* I/O counter: bytes written */
      p->syscr = 0;           /* I/O counter: read syscalls */
      p->syscw = 0;           /* I/O counter: write syscalls */
#endif
      task_io_accounting_init(p);
      acct_clear_integrals(p);

      p->it_virt_expires = cputime_zero;
      p->it_prof_expires = cputime_zero;
      p->it_sched_expires = 0;
      INIT_LIST_HEAD(&p->cpu_timers[0]);
      INIT_LIST_HEAD(&p->cpu_timers[1]);
      INIT_LIST_HEAD(&p->cpu_timers[2]);

      p->lock_depth = -1;           /* -1 = no lock */
      do_posix_clock_monotonic_gettime(&p->start_time);
      p->real_start_time = p->start_time;
      monotonic_to_bootbased(&p->real_start_time);
#ifdef CONFIG_SECURITY
      p->security = NULL;
#endif
      p->io_context = NULL;
      p->audit_context = NULL;
      cgroup_fork(p);
#ifdef CONFIG_NUMA
      p->mempolicy = mpol_copy(p->mempolicy);
      if (IS_ERR(p->mempolicy)) {
            retval = PTR_ERR(p->mempolicy);
            p->mempolicy = NULL;
            goto bad_fork_cleanup_cgroup;
      }
      mpol_fix_fork_child_flag(p);
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
      p->irq_events = 0;
#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
      p->hardirqs_enabled = 1;
#else
      p->hardirqs_enabled = 0;
#endif
      p->hardirq_enable_ip = 0;
      p->hardirq_enable_event = 0;
      p->hardirq_disable_ip = _THIS_IP_;
      p->hardirq_disable_event = 0;
      p->softirqs_enabled = 1;
      p->softirq_enable_ip = _THIS_IP_;
      p->softirq_enable_event = 0;
      p->softirq_disable_ip = 0;
      p->softirq_disable_event = 0;
      p->hardirq_context = 0;
      p->softirq_context = 0;
#endif
#ifdef CONFIG_LOCKDEP
      p->lockdep_depth = 0; /* no locks held yet */
      p->curr_chain_key = 0;
      p->lockdep_recursion = 0;
#endif

#ifdef CONFIG_DEBUG_MUTEXES
      p->blocked_on = NULL; /* not blocked yet */
#endif

      /* Perform scheduler related setup. Assign this task to a CPU. */
      sched_fork(p, clone_flags);

      if ((retval = security_task_alloc(p)))
            goto bad_fork_cleanup_policy;
      if ((retval = audit_alloc(p)))
            goto bad_fork_cleanup_security;
      /* copy all the process information */
      if ((retval = copy_semundo(clone_flags, p)))
            goto bad_fork_cleanup_audit;
      if ((retval = copy_files(clone_flags, p)))
            goto bad_fork_cleanup_semundo;
      if ((retval = copy_fs(clone_flags, p)))
            goto bad_fork_cleanup_files;
      if ((retval = copy_sighand(clone_flags, p)))
            goto bad_fork_cleanup_fs;
      if ((retval = copy_signal(clone_flags, p)))
            goto bad_fork_cleanup_sighand;
      if ((retval = copy_mm(clone_flags, p)))
            goto bad_fork_cleanup_signal;
      if ((retval = copy_keys(clone_flags, p)))
            goto bad_fork_cleanup_mm;
      if ((retval = copy_namespaces(clone_flags, p)))
            goto bad_fork_cleanup_keys;
      retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
      if (retval)
            goto bad_fork_cleanup_namespaces;

      if (pid != &init_struct_pid) {
            retval = -ENOMEM;
            pid = alloc_pid(task_active_pid_ns(p));
            if (!pid)
                  goto bad_fork_cleanup_namespaces;

            if (clone_flags & CLONE_NEWPID) {
                  retval = pid_ns_prepare_proc(task_active_pid_ns(p));
                  if (retval < 0)
                        goto bad_fork_free_pid;
            }
      }

      p->pid = pid_nr(pid);
      p->tgid = p->pid;
      if (clone_flags & CLONE_THREAD)
            p->tgid = current->tgid;

      p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
      /*
       * Clear TID on mm_release()?
       */
      p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
#ifdef CONFIG_FUTEX
      p->robust_list = NULL;
#ifdef CONFIG_COMPAT
      p->compat_robust_list = NULL;
#endif
      INIT_LIST_HEAD(&p->pi_state_list);
      p->pi_state_cache = NULL;
#endif
      /*
       * sigaltstack should be cleared when sharing the same VM
       */
      if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
            p->sas_ss_sp = p->sas_ss_size = 0;

      /*
       * Syscall tracing should be turned off in the child regardless
       * of CLONE_PTRACE.
       */
      clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
#ifdef TIF_SYSCALL_EMU
      clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
#endif

      /* Our parent execution domain becomes current domain
         These must match for thread signalling to apply */
      p->parent_exec_id = p->self_exec_id;

      /* ok, now we should be set up.. */
      p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
      p->pdeath_signal = 0;
      p->exit_state = 0;

      /*
       * Ok, make it visible to the rest of the system.
       * We dont wake it up yet.
       */
      p->group_leader = p;
      INIT_LIST_HEAD(&p->thread_group);
      INIT_LIST_HEAD(&p->ptrace_children);
      INIT_LIST_HEAD(&p->ptrace_list);

      /* Now that the task is set up, run cgroup callbacks if
       * necessary. We need to run them before the task is visible
       * on the tasklist. */
      cgroup_fork_callbacks(p);
      cgroup_callbacks_done = 1;

      /* Need tasklist lock for parent etc handling! */
      write_lock_irq(&tasklist_lock);

      /* for sys_ioprio_set(IOPRIO_WHO_PGRP) */
      p->ioprio = current->ioprio;

      /*
       * The task hasn't been attached yet, so its cpus_allowed mask will
       * not be changed, nor will its assigned CPU.
       *
       * The cpus_allowed mask of the parent may have changed after it was
       * copied first time - so re-copy it here, then check the child's CPU
       * to ensure it is on a valid CPU (and if not, just force it back to
       * parent's CPU). This avoids alot of nasty races.
       */
      p->cpus_allowed = current->cpus_allowed;
      if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed) ||
                  !cpu_online(task_cpu(p))))
            set_task_cpu(p, smp_processor_id());

      /* CLONE_PARENT re-uses the old parent */
      if (clone_flags & (CLONE_PARENT|CLONE_THREAD))
            p->real_parent = current->real_parent;
      else
            p->real_parent = current;
      p->parent = p->real_parent;

      spin_lock(&current->sighand->siglock);

      /*
       * Process group and session signals need to be delivered to just the
       * parent before the fork or both the parent and the child after the
       * fork. Restart if a signal comes in before we add the new process to
       * it's process group.
       * A fatal signal pending means that current will exit, so the new
       * thread can't slip out of an OOM kill (or normal SIGKILL).
       */
      recalc_sigpending();
      if (signal_pending(current)) {
            spin_unlock(&current->sighand->siglock);
            write_unlock_irq(&tasklist_lock);
            retval = -ERESTARTNOINTR;
            goto bad_fork_free_pid;
      }

      if (clone_flags & CLONE_THREAD) {
            p->group_leader = current->group_leader;
            list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);

            if (!cputime_eq(current->signal->it_virt_expires,
                        cputime_zero) ||
                !cputime_eq(current->signal->it_prof_expires,
                        cputime_zero) ||
                current->signal->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY ||
                !list_empty(&current->signal->cpu_timers[0]) ||
                !list_empty(&current->signal->cpu_timers[1]) ||
                !list_empty(&current->signal->cpu_timers[2])) {
                  /*
                   * Have child wake up on its first tick to check
                   * for process CPU timers.
                   */
                  p->it_prof_expires = jiffies_to_cputime(1);
            }
      }

      if (likely(p->pid)) {
            add_parent(p);
            if (unlikely(p->ptrace & PT_PTRACED))
                  __ptrace_link(p, current->parent);

            if (thread_group_leader(p)) {
                  if (clone_flags & CLONE_NEWPID)
                        p->nsproxy->pid_ns->child_reaper = p;

                  p->signal->tty = current->signal->tty;
                  set_task_pgrp(p, task_pgrp_nr(current));
                  set_task_session(p, task_session_nr(current));
                  attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
                  attach_pid(p, PIDTYPE_SID, task_session(current));
                  list_add_tail_rcu(&p->tasks, &init_task.tasks);
                  __get_cpu_var(process_counts)++;
            }
            attach_pid(p, PIDTYPE_PID, pid);
            nr_threads++;
      }

      total_forks++;
      spin_unlock(&current->sighand->siglock);
      write_unlock_irq(&tasklist_lock);
      proc_fork_connector(p);
      cgroup_post_fork(p);
      return p;

bad_fork_free_pid:
      if (pid != &init_struct_pid)
            free_pid(pid);
bad_fork_cleanup_namespaces:
      exit_task_namespaces(p);
bad_fork_cleanup_keys:
      exit_keys(p);
bad_fork_cleanup_mm:
      if (p->mm)
            mmput(p->mm);
bad_fork_cleanup_signal:
      cleanup_signal(p);
bad_fork_cleanup_sighand:
      __cleanup_sighand(p->sighand);
bad_fork_cleanup_fs:
      exit_fs(p); /* blocking */
bad_fork_cleanup_files:
      exit_files(p); /* blocking */
bad_fork_cleanup_semundo:
      exit_sem(p);
bad_fork_cleanup_audit:
      audit_free(p);
bad_fork_cleanup_security:
      security_task_free(p);
bad_fork_cleanup_policy:
#ifdef CONFIG_NUMA
      mpol_free(p->mempolicy);
bad_fork_cleanup_cgroup:
#endif
      cgroup_exit(p, cgroup_callbacks_done);
      delayacct_tsk_free(p);
      if (p->binfmt)
            module_put(p->binfmt->module);
bad_fork_cleanup_put_domain:
      module_put(task_thread_info(p)->exec_domain->module);
bad_fork_cleanup_count:
      put_group_info(p->group_info);
      atomic_dec(&p->user->processes);
      free_uid(p->user);
bad_fork_free:
      free_task(p);
fork_out:
      return ERR_PTR(retval);
}

noinline struct pt_regs * __devinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
{
      memset(regs, 0, sizeof(struct pt_regs));
      return regs;
}

struct task_struct * __cpuinit fork_idle(int cpu)
{
      struct task_struct *task;
      struct pt_regs regs;

      task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
                        &init_struct_pid);
      if (!IS_ERR(task))
            init_idle(task, cpu);

      return task;
}

static int fork_traceflag(unsigned clone_flags)
{
      if (clone_flags & CLONE_UNTRACED)
            return 0;
      else if (clone_flags & CLONE_VFORK) {
            if (current->ptrace & PT_TRACE_VFORK)
                  return PTRACE_EVENT_VFORK;
      } else if ((clone_flags & CSIGNAL) != SIGCHLD) {
            if (current->ptrace & PT_TRACE_CLONE)
                  return PTRACE_EVENT_CLONE;
      } else if (current->ptrace & PT_TRACE_FORK)
            return PTRACE_EVENT_FORK;

      return 0;
}

/*
 *  Ok, this is the main fork-routine.
 *
 * It copies the process, and if successful kick-starts
 * it and waits for it to finish using the VM if required.
 */
long do_fork(unsigned long clone_flags,
            unsigned long stack_start,
            struct pt_regs *regs,
            unsigned long stack_size,
            int __user *parent_tidptr,
            int __user *child_tidptr)
{
      struct task_struct *p;
      int trace = 0;
      long nr;

      if (unlikely(current->ptrace)) {
            trace = fork_traceflag (clone_flags);
            if (trace)
                  clone_flags |= CLONE_PTRACE;
      }

      p = copy_process(clone_flags, stack_start, regs, stack_size,
                  child_tidptr, NULL);
      /*
       * Do this prior waking up the new thread - the thread pointer
       * might get invalid after that point, if the thread exits quickly.
       */
      if (!IS_ERR(p)) {
            struct completion vfork;

            /*
             * this is enough to call pid_nr_ns here, but this if
             * improves optimisation of regular fork()
             */
            nr = (clone_flags & CLONE_NEWPID) ?
                  task_pid_nr_ns(p, current->nsproxy->pid_ns) :
                        task_pid_vnr(p);

            if (clone_flags & CLONE_PARENT_SETTID)
                  put_user(nr, parent_tidptr);

            if (clone_flags & CLONE_VFORK) {
                  p->vfork_done = &vfork;
                  init_completion(&vfork);
            }

            if ((p->ptrace & PT_PTRACED) || (clone_flags & CLONE_STOPPED)) {
                  /*
                   * We'll start up with an immediate SIGSTOP.
                   */
                  sigaddset(&p->pending.signal, SIGSTOP);
                  set_tsk_thread_flag(p, TIF_SIGPENDING);
            }

            if (!(clone_flags & CLONE_STOPPED))
                  wake_up_new_task(p, clone_flags);
            else
                  p->state = TASK_STOPPED;

            if (unlikely (trace)) {
                  current->ptrace_message = nr;
                  ptrace_notify ((trace << 8) | SIGTRAP);
            }

            if (clone_flags & CLONE_VFORK) {
                  freezer_do_not_count();
                  wait_for_completion(&vfork);
                  freezer_count();
                  if (unlikely (current->ptrace & PT_TRACE_VFORK_DONE)) {
                        current->ptrace_message = nr;
                        ptrace_notify ((PTRACE_EVENT_VFORK_DONE << 8) | SIGTRAP);
                  }
            }
      } else {
            nr = PTR_ERR(p);
      }
      return nr;
}

#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif

static void sighand_ctor(struct kmem_cache *cachep, void *data)
{
      struct sighand_struct *sighand = data;

      spin_lock_init(&sighand->siglock);
      init_waitqueue_head(&sighand->signalfd_wqh);
}

void __init proc_caches_init(void)
{
      sighand_cachep = kmem_cache_create("sighand_cache",
                  sizeof(struct sighand_struct), 0,
                  SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU,
                  sighand_ctor);
      signal_cachep = kmem_cache_create("signal_cache",
                  sizeof(struct signal_struct), 0,
                  SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
      files_cachep = kmem_cache_create("files_cache",
                  sizeof(struct files_struct), 0,
                  SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
      fs_cachep = kmem_cache_create("fs_cache",
                  sizeof(struct fs_struct), 0,
                  SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
      vm_area_cachep = kmem_cache_create("vm_area_struct",
                  sizeof(struct vm_area_struct), 0,
                  SLAB_PANIC, NULL);
      mm_cachep = kmem_cache_create("mm_struct",
                  sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
                  SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
}

/*
 * Check constraints on flags passed to the unshare system call and
 * force unsharing of additional process context as appropriate.
 */
static void check_unshare_flags(unsigned long *flags_ptr)
{
      /*
       * If unsharing a thread from a thread group, must also
       * unshare vm.
       */
      if (*flags_ptr & CLONE_THREAD)
            *flags_ptr |= CLONE_VM;

      /*
       * If unsharing vm, must also unshare signal handlers.
       */
      if (*flags_ptr & CLONE_VM)
            *flags_ptr |= CLONE_SIGHAND;

      /*
       * If unsharing signal handlers and the task was created
       * using CLONE_THREAD, then must unshare the thread
       */
      if ((*flags_ptr & CLONE_SIGHAND) &&
          (atomic_read(&current->signal->count) > 1))
            *flags_ptr |= CLONE_THREAD;

      /*
       * If unsharing namespace, must also unshare filesystem information.
       */
      if (*flags_ptr & CLONE_NEWNS)
            *flags_ptr |= CLONE_FS;
}

/*
 * Unsharing of tasks created with CLONE_THREAD is not supported yet
 */
static int unshare_thread(unsigned long unshare_flags)
{
      if (unshare_flags & CLONE_THREAD)
            return -EINVAL;

      return 0;
}

/*
 * Unshare the filesystem structure if it is being shared
 */
static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
{
      struct fs_struct *fs = current->fs;

      if ((unshare_flags & CLONE_FS) &&
          (fs && atomic_read(&fs->count) > 1)) {
            *new_fsp = __copy_fs_struct(current->fs);
            if (!*new_fsp)
                  return -ENOMEM;
      }

      return 0;
}

/*
 * Unsharing of sighand is not supported yet
 */
static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
{
      struct sighand_struct *sigh = current->sighand;

      if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)
            return -EINVAL;
      else
            return 0;
}

/*
 * Unshare vm if it is being shared
 */
static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
{
      struct mm_struct *mm = current->mm;

      if ((unshare_flags & CLONE_VM) &&
          (mm && atomic_read(&mm->mm_users) > 1)) {
            return -EINVAL;
      }

      return 0;
}

/*
 * Unshare file descriptor table if it is being shared
 */
static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
{
      struct files_struct *fd = current->files;
      int error = 0;

      if ((unshare_flags & CLONE_FILES) &&
          (fd && atomic_read(&fd->count) > 1)) {
            *new_fdp = dup_fd(fd, &error);
            if (!*new_fdp)
                  return error;
      }

      return 0;
}

/*
 * Unsharing of semundo for tasks created with CLONE_SYSVSEM is not
 * supported yet
 */
static int unshare_semundo(unsigned long unshare_flags, struct sem_undo_list **new_ulistp)
{
      if (unshare_flags & CLONE_SYSVSEM)
            return -EINVAL;

      return 0;
}

/*
 * unshare allows a process to 'unshare' part of the process
 * context which was originally shared using clone.  copy_*
 * functions used by do_fork() cannot be used here directly
 * because they modify an inactive task_struct that is being
 * constructed. Here we are modifying the current, active,
 * task_struct.
 */
asmlinkage long sys_unshare(unsigned long unshare_flags)
{
      int err = 0;
      struct fs_struct *fs, *new_fs = NULL;
      struct sighand_struct *new_sigh = NULL;
      struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
      struct files_struct *fd, *new_fd = NULL;
      struct sem_undo_list *new_ulist = NULL;
      struct nsproxy *new_nsproxy = NULL;

      check_unshare_flags(&unshare_flags);

      /* Return -EINVAL for all unsupported flags */
      err = -EINVAL;
      if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
                        CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
                        CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|
                        CLONE_NEWNET))
            goto bad_unshare_out;

      if ((err = unshare_thread(unshare_flags)))
            goto bad_unshare_out;
      if ((err = unshare_fs(unshare_flags, &new_fs)))
            goto bad_unshare_cleanup_thread;
      if ((err = unshare_sighand(unshare_flags, &new_sigh)))
            goto bad_unshare_cleanup_fs;
      if ((err = unshare_vm(unshare_flags, &new_mm)))
            goto bad_unshare_cleanup_sigh;
      if ((err = unshare_fd(unshare_flags, &new_fd)))
            goto bad_unshare_cleanup_vm;
      if ((err = unshare_semundo(unshare_flags, &new_ulist)))
            goto bad_unshare_cleanup_fd;
      if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
                  new_fs)))
            goto bad_unshare_cleanup_semundo;

      if (new_fs ||  new_mm || new_fd || new_ulist || new_nsproxy) {

            if (new_nsproxy) {
                  switch_task_namespaces(current, new_nsproxy);
                  new_nsproxy = NULL;
            }

            task_lock(current);

            if (new_fs) {
                  fs = current->fs;
                  current->fs = new_fs;
                  new_fs = fs;
            }

            if (new_mm) {
                  mm = current->mm;
                  active_mm = current->active_mm;
                  current->mm = new_mm;
                  current->active_mm = new_mm;
                  activate_mm(active_mm, new_mm);
                  new_mm = mm;
            }

            if (new_fd) {
                  fd = current->files;
                  current->files = new_fd;
                  new_fd = fd;
            }

            task_unlock(current);
      }

      if (new_nsproxy)
            put_nsproxy(new_nsproxy);

bad_unshare_cleanup_semundo:
bad_unshare_cleanup_fd:
      if (new_fd)
            put_files_struct(new_fd);

bad_unshare_cleanup_vm:
      if (new_mm)
            mmput(new_mm);

bad_unshare_cleanup_sigh:
      if (new_sigh)
            if (atomic_dec_and_test(&new_sigh->count))
                  kmem_cache_free(sighand_cachep, new_sigh);

bad_unshare_cleanup_fs:
      if (new_fs)
            put_fs_struct(new_fs);

bad_unshare_cleanup_thread:
bad_unshare_out:
      return err;
}

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