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[linux-2.6] / kernel / 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/fdtable.h>
#include <linux/iocontext.h>
#include <linux/key.h>
#include <linux/binfmts.h>
#include <linux/mman.h>
#include <linux/mmu_notifier.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/hugetlb.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/jiffies.h>
#include <linux/tracehook.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/memcontrol.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 <linux/blkdev.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

#ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
static inline struct thread_info *alloc_thread_info(struct task_struct *tsk)
{
#ifdef CONFIG_DEBUG_STACK_USAGE
        gfp_t mask = GFP_KERNEL | __GFP_ZERO;
#else
        gfp_t mask = GFP_KERNEL;
#endif
        return (struct thread_info *)__get_free_pages(mask, THREAD_SIZE_ORDER);
}

static inline void free_thread_info(struct thread_info *ti)
{
        free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
}
#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);
}

/*
 * macro override instead of weak attribute alias, to workaround
 * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
 */
#ifndef arch_task_cache_init
#define arch_task_cache_init()
#endif

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

        /* do the arch specific task caches init */
        arch_task_cache_init();

        /*
         * 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];
}

int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
                                               struct task_struct *src)
{
        *dst = *src;
        return 0;
}

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;
        }

        err = arch_dup_task_struct(tsk, orig);
        if (err)
                goto out;

        tsk->stack = ti;

        err = prop_local_init_single(&tsk->dirties);
        if (err)
                goto out;

        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;

out:
        free_thread_info(ti);
        free_task_struct(tsk);
        return NULL;
}

#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_dup(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);
                }

                /*
                 * Clear hugetlb-related page reserves for children. This only
                 * affects MAP_PRIVATE mappings. Faults generated by the child
                 * are not guaranteed to succeed, even if read-only
                 */
                if (is_vm_hugetlb_page(tmp))
                        reset_vma_resv_huge_pages(tmp);

                /*
                 * 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, 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, struct task_struct *p)
{
        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_state = NULL;
        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;
        mm_init_owner(mm, p);

        if (likely(!mm_alloc_pgd(mm))) {
                mm->def_flags = 0;
                mmu_notifier_mm_init(mm);
                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, current);
        }
        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 __mmdrop(struct mm_struct *mm)
{
        BUG_ON(mm == &init_mm);
        mm_free_pgd(mm);
        destroy_context(mm);
        mmu_notifier_mm_destroy(mm);
        free_mm(mm);
}
EXPORT_SYMBOL_GPL(__mmdrop);

/*
 * 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);
                set_mm_exe_file(mm, NULL);
                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_KTHREAD (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_KTHREAD)
                        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.
 */
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, tsk))
                goto fail_nomem;

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

        dup_mm_exe_file(oldmm, mm);

        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->root = old->root;
                path_get(&old->root);
                fs->pwd = old->pwd;
                path_get(&old->pwd);
                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 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;
        }

        newf = dup_fd(oldf, &error);
        if (!newf)
                goto out;

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

static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
{
#ifdef CONFIG_BLOCK
        struct io_context *ioc = current->io_context;

        if (!ioc)
                return 0;
        /*
         * Share io context with parent, if CLONE_IO is set
         */
        if (clone_flags & CLONE_IO) {
                tsk->io_context = ioc_task_link(ioc);
                if (unlikely(!tsk->io_context))
                        return -ENOMEM;
        } else if (ioprio_valid(ioc->ioprio)) {
                tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
                if (unlikely(!tsk->io_context))
                        return -ENOMEM;

                tsk->io_context->ioprio = ioc->ioprio;
        }
#endif
        return 0;
}

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 = tsk;
        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->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;
        task_io_accounting_init(&sig->ioac);
        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;
        new_flags |= PF_STARTING;
        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
}

#ifdef CONFIG_MM_OWNER
void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
{
        mm->owner = p;
}
#endif /* CONFIG_MM_OWNER */

/*
 * 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 trace)
{
        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_PROVE_LOCKING
        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);
#ifdef CONFIG_PREEMPT_RCU
        p->rcu_read_lock_nesting = 0;
        p->rcu_flipctr_idx = 0;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
        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_DETECT_SOFTLOCKUP
        p->last_switch_count = 0;
        p->last_switch_timestamp = 0;
#endif

        task_io_accounting_init(&p->ioac);
        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->cap_bset = current->cap_bset;
        p->io_context = NULL;
        p->audit_context = NULL;
        cgroup_fork(p);
#ifdef CONFIG_NUMA
        p->mempolicy = mpol_dup(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;
        if ((retval = copy_io(clone_flags, p)))
                goto bad_fork_cleanup_namespaces;
        retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
        if (retval)
                goto bad_fork_cleanup_io;

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

                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;

        if (current->nsproxy != p->nsproxy) {
                retval = ns_cgroup_clone(p, pid);
                if (retval)
                        goto bad_fork_free_pid;
        }

        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
        clear_all_latency_tracing(p);

        /* 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);

        /* 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);

        /*
         * 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;
        p->rt.nr_cpus_allowed = current->rt.nr_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;

        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)) {
                list_add_tail(&p->sibling, &p->real_parent->children);
                tracehook_finish_clone(p, clone_flags, trace);

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

                        p->signal->leader_pid = pid;
                        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_io:
        put_io_context(p->io_context);
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_put(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 * __cpuinit __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, 0);
        if (!IS_ERR(task))
                init_idle(task, cpu);

        return task;
}

/*
 *  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;

        /*
         * We hope to recycle these flags after 2.6.26
         */
        if (unlikely(clone_flags & CLONE_STOPPED)) {
                static int __read_mostly count = 100;

                if (count > 0 && printk_ratelimit()) {
                        char comm[TASK_COMM_LEN];

                        count--;
                        printk(KERN_INFO "fork(): process `%s' used deprecated "
                                        "clone flags 0x%lx\n",
                                get_task_comm(comm, current),
                                clone_flags & CLONE_STOPPED);
                }
        }

        /*
         * When called from kernel_thread, don't do user tracing stuff.
         */
        if (likely(user_mode(regs)))
                trace = tracehook_prepare_clone(clone_flags);

        p = copy_process(clone_flags, stack_start, regs, stack_size,
                         child_tidptr, NULL, trace);
        /*
         * 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;

                nr = 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);
                }

                tracehook_report_clone(trace, regs, clone_flags, nr, p);

                /*
                 * We set PF_STARTING at creation in case tracing wants to
                 * use this to distinguish a fully live task from one that
                 * hasn't gotten to tracehook_report_clone() yet.  Now we
                 * clear it and set the child going.
                 */
                p->flags &= ~PF_STARTING;

                if (unlikely(clone_flags & CLONE_STOPPED)) {
                        /*
                         * We'll start up with an immediate SIGSTOP.
                         */
                        sigaddset(&p->pending.signal, SIGSTOP);
                        set_tsk_thread_flag(p, TIF_SIGPENDING);
                        __set_task_state(p, TASK_STOPPED);
                } else {
                        wake_up_new_task(p, clone_flags);
                }

                tracehook_report_clone_complete(trace, regs,
                                                clone_flags, nr, p);

                if (clone_flags & CLONE_VFORK) {
                        freezer_do_not_count();
                        wait_for_completion(&vfork);
                        freezer_count();
                        tracehook_report_vfork_done(p, nr);
                }
        } else {
                nr = PTR_ERR(p);
        }
        return nr;
}

#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif

static void sighand_ctor(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;
}

/*
 * 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 nsproxy *new_nsproxy = NULL;
        int do_sysvsem = 0;

        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;

        /*
         * CLONE_NEWIPC must also detach from the undolist: after switching
         * to a new ipc namespace, the semaphore arrays from the old
         * namespace are unreachable.
         */
        if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
                do_sysvsem = 1;
        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_nsproxy_namespaces(unshare_flags, &new_nsproxy,
                        new_fs)))
                goto bad_unshare_cleanup_fd;

        if (new_fs ||  new_mm || new_fd || do_sysvsem || new_nsproxy) {
                if (do_sysvsem) {
                        /*
                         * CLONE_SYSVSEM is equivalent to sys_exit().
                         */
                        exit_sem(current);
                }

                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_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;
}

/*
 *      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(struct files_struct **displaced)
{
        struct task_struct *task = current;
        struct files_struct *copy = NULL;
        int error;

        error = unshare_fd(CLONE_FILES, &copy);
        if (error || !copy) {
                *displaced = NULL;
                return error;
        }
        *displaced = task->files;
        task_lock(task);
        task->files = copy;
        task_unlock(task);
        return 0;
}