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[linux-2.6.9-moxart.git] / 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/config.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#include <linux/completion.h>
#include <linux/namespace.h>
#include <linux/personality.h>
#include <linux/mempolicy.h>
#include <linux/sem.h>
#include <linux/file.h>
#include <linux/binfmts.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/cpu.h>
#include <linux/security.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/jiffies.h>
#include <linux/futex.h>
#include <linux/ptrace.h>
#include <linux/mount.h>
#include <linux/audit.h>
#include <linux/profile.h>
#include <linux/rmap.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>

/* The idle threads do not count..
 * Protected by write_lock_irq(&tasklist_lock)
 */
int nr_threads;

int max_threads;
unsigned long total_forks;      /* Handle normal Linux uptimes. */

DEFINE_PER_CPU(unsigned long, process_counts) = 0;

rwlock_t tasklist_lock __cacheline_aligned = RW_LOCK_UNLOCKED;  /* outer */

EXPORT_SYMBOL(tasklist_lock);

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 kmem_cache_t *task_struct_cachep;
#endif

void free_task(struct task_struct *tsk)
{
        free_thread_info(tsk->thread_info);
        free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);

void __put_task_struct(struct task_struct *tsk)
{
        WARN_ON(!(tsk->state & (TASK_DEAD | TASK_ZOMBIE)));
        WARN_ON(atomic_read(&tsk->usage));
        WARN_ON(tsk == current);

        if (unlikely(tsk->audit_context))
                audit_free(tsk);
        security_task_free(tsk);
        free_uid(tsk->user);
        put_group_info(tsk->group_info);

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

void fastcall add_wait_queue(wait_queue_head_t *q, wait_queue_t * wait)
{
        unsigned long flags;

        wait->flags &= ~WQ_FLAG_EXCLUSIVE;
        spin_lock_irqsave(&q->lock, flags);
        __add_wait_queue(q, wait);
        spin_unlock_irqrestore(&q->lock, flags);
}

EXPORT_SYMBOL(add_wait_queue);

void fastcall add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t * wait)
{
        unsigned long flags;

        wait->flags |= WQ_FLAG_EXCLUSIVE;
        spin_lock_irqsave(&q->lock, flags);
        __add_wait_queue_tail(q, wait);
        spin_unlock_irqrestore(&q->lock, flags);
}

EXPORT_SYMBOL(add_wait_queue_exclusive);

void fastcall remove_wait_queue(wait_queue_head_t *q, wait_queue_t * wait)
{
        unsigned long flags;

        spin_lock_irqsave(&q->lock, flags);
        __remove_wait_queue(q, wait);
        spin_unlock_irqrestore(&q->lock, flags);
}

EXPORT_SYMBOL(remove_wait_queue);


/*
 * Note: we use "set_current_state()" _after_ the wait-queue add,
 * because we need a memory barrier there on SMP, so that any
 * wake-function that tests for the wait-queue being active
 * will be guaranteed to see waitqueue addition _or_ subsequent
 * tests in this thread will see the wakeup having taken place.
 *
 * The spin_unlock() itself is semi-permeable and only protects
 * one way (it only protects stuff inside the critical region and
 * stops them from bleeding out - it would still allow subsequent
 * loads to move into the the critical region).
 */
void fastcall prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
        unsigned long flags;

        wait->flags &= ~WQ_FLAG_EXCLUSIVE;
        spin_lock_irqsave(&q->lock, flags);
        if (list_empty(&wait->task_list))
                __add_wait_queue(q, wait);
        /*
         * don't alter the task state if this is just going to
         * queue an async wait queue callback
         */
        if (is_sync_wait(wait))
                set_current_state(state);
        spin_unlock_irqrestore(&q->lock, flags);
}

EXPORT_SYMBOL(prepare_to_wait);

void fastcall
prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
        unsigned long flags;

        wait->flags |= WQ_FLAG_EXCLUSIVE;
        spin_lock_irqsave(&q->lock, flags);
        if (list_empty(&wait->task_list))
                __add_wait_queue_tail(q, wait);
        /*
         * don't alter the task state if this is just going to
         * queue an async wait queue callback
         */
        if (is_sync_wait(wait))
                set_current_state(state);
        spin_unlock_irqrestore(&q->lock, flags);
}

EXPORT_SYMBOL(prepare_to_wait_exclusive);

void fastcall finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
{
        unsigned long flags;

        __set_current_state(TASK_RUNNING);
        /*
         * We can check for list emptiness outside the lock
         * IFF:
         *  - we use the "careful" check that verifies both
         *    the next and prev pointers, so that there cannot
         *    be any half-pending updates in progress on other
         *    CPU's that we haven't seen yet (and that might
         *    still change the stack area.
         * and
         *  - all other users take the lock (ie we can only
         *    have _one_ other CPU that looks at or modifies
         *    the list).
         */
        if (!list_empty_careful(&wait->task_list)) {
                spin_lock_irqsave(&q->lock, flags);
                list_del_init(&wait->task_list);
                spin_unlock_irqrestore(&q->lock, flags);
        }
}

EXPORT_SYMBOL(finish_wait);

int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
        int ret = default_wake_function(wait, mode, sync, key);

        if (ret)
                list_del_init(&wait->task_list);
        return ret;
}

EXPORT_SYMBOL(autoremove_wake_function);

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, 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 / (THREAD_SIZE/PAGE_SIZE) / 8;
        /*
         * we need to allow at least 20 threads to boot a system
         */
        if(max_threads < 20)
                max_threads = 20;

        init_task.rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
        init_task.rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
}

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

        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;
        }

        *ti = *orig->thread_info;
        *tsk = *orig;
        tsk->thread_info = ti;
        ti->task = tsk;

        /* One for us, one for whoever does the "release_task()" (usually parent) */
        atomic_set(&tsk->usage,2);
        return tsk;
}

#ifdef CONFIG_MMU
static inline 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_mm(current->mm);
        mm->locked_vm = 0;
        mm->mmap = NULL;
        mm->mmap_cache = NULL;
        mm->free_area_cache = oldmm->mmap_base;
        mm->map_count = 0;
        mm->rss = 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;

        /*
         * Add it to the mmlist after the parent.
         * Doing it this way means that we can order the list,
         * and fork() won't mess up the ordering significantly.
         * Add it first so that swapoff can see any swap entries.
         */
        spin_lock(&mmlist_lock);
        list_add(&mm->mmlist, &current->mm->mmlist);
        mmlist_nr++;
        spin_unlock(&mmlist_lock);

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

                if (mpnt->vm_flags & VM_DONTCOPY) {
                        __vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
                                                        -vma_pages(mpnt));
                        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, SLAB_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_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);
                        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:
                 * link in first so that swapoff can see swap entries,
                 * and try_to_unmap_one's find_vma find the new vma.
                 */
                spin_lock(&mm->page_table_lock);
                *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, current->mm, tmp);
                spin_unlock(&mm->page_table_lock);

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

                if (retval)
                        goto out;
        }
        retval = 0;

out:
        flush_tlb_mm(current->mm);
        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 */

spinlock_t mmlist_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
int mmlist_nr;

#define allocate_mm()   (kmem_cache_alloc(mm_cachep, SLAB_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);
        mm->core_waiters = 0;
        mm->page_table_lock = SPIN_LOCK_UNLOCKED;
        mm->ioctx_list_lock = RW_LOCK_UNLOCKED;
        mm->ioctx_list = NULL;
        mm->default_kioctx = (struct kioctx)INIT_KIOCTX(mm->default_kioctx, *mm);
        mm->free_area_cache = TASK_UNMAPPED_BASE;

        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)
{
        if (atomic_dec_and_lock(&mm->mm_users, &mmlist_lock)) {
                list_del(&mm->mmlist);
                mmlist_nr--;
                spin_unlock(&mmlist_lock);
                exit_aio(mm);
                exit_mmap(mm);
                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 if the use count
 * of the mm is non-zero 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.
 *
 * If the use count is zero, it means that this mm is going away,
 * so return %NULL.  This only happens in the case of an AIO daemon
 * which has temporarily adopted an mm (see use_mm), in the course
 * of its final mmput, before exit_aio has completed.
 */
struct mm_struct *get_task_mm(struct task_struct *task)
{
        struct mm_struct *mm;

        task_lock(task);
        mm = task->mm;
        if (mm) {
                spin_lock(&mmlist_lock);
                if (!atomic_read(&mm->mm_users))
                        mm = NULL;
                else
                        atomic_inc(&mm->mm_users);
                spin_unlock(&mmlist_lock);
        }
        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 (tsk->clear_child_tid && 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);
        }
}

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;
                /*
                 * There are cases where the PTL is held to ensure no
                 * new threads start up in user mode using an mm, which
                 * allows optimizing out ipis; the tlb_gather_mmu code
                 * is an example.
                 */
                spin_unlock_wait(&oldmm->page_table_lock);
                goto good_mm;
        }

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

        /* Copy the current MM stuff.. */
        memcpy(mm, oldmm, sizeof(*mm));
        if (!mm_init(mm))
                goto fail_nomem;

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

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

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

free_pt:
        mmput(mm);
fail_nomem:
        return retval;

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 retval;
}

static inline 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);
                fs->lock = RW_LOCK_UNLOCKED;
                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 inline 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 files_struct *files, int size)
{
        int i;

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

static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
        struct files_struct *oldf, *newf;
        struct file **old_fds, **new_fds;
        int open_files, nfds, size, i, 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;
        error = -ENOMEM;
        newf = kmem_cache_alloc(files_cachep, SLAB_KERNEL);
        if (!newf) 
                goto out;

        atomic_set(&newf->count, 1);

        newf->file_lock     = SPIN_LOCK_UNLOCKED;
        newf->next_fd       = 0;
        newf->max_fds       = NR_OPEN_DEFAULT;
        newf->max_fdset     = __FD_SETSIZE;
        newf->close_on_exec = &newf->close_on_exec_init;
        newf->open_fds      = &newf->open_fds_init;
        newf->fd            = &newf->fd_array[0];

        /* We don't yet have the oldf readlock, but even if the old
           fdset gets grown now, we'll only copy up to "size" fds */
        size = oldf->max_fdset;
        if (size > __FD_SETSIZE) {
                newf->max_fdset = 0;
                spin_lock(&newf->file_lock);
                error = expand_fdset(newf, size-1);
                spin_unlock(&newf->file_lock);
                if (error)
                        goto out_release;
        }
        spin_lock(&oldf->file_lock);

        open_files = count_open_files(oldf, size);

        /*
         * Check whether we need to allocate a larger fd array.
         * Note: we're not a clone task, so the open count won't
         * change.
         */
        nfds = NR_OPEN_DEFAULT;
        if (open_files > nfds) {
                spin_unlock(&oldf->file_lock);
                newf->max_fds = 0;
                spin_lock(&newf->file_lock);
                error = expand_fd_array(newf, open_files-1);
                spin_unlock(&newf->file_lock);
                if (error) 
                        goto out_release;
                nfds = newf->max_fds;
                spin_lock(&oldf->file_lock);
        }

        old_fds = oldf->fd;
        new_fds = newf->fd;

        memcpy(newf->open_fds->fds_bits, oldf->open_fds->fds_bits, open_files/8);
        memcpy(newf->close_on_exec->fds_bits, oldf->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);
                *new_fds++ = f;
        }
        spin_unlock(&oldf->file_lock);

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

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

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

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

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

out_release:
        free_fdset (newf->close_on_exec, newf->max_fdset);
        free_fdset (newf->open_fds, newf->max_fdset);
        kmem_cache_free(files_cachep, newf);
        goto out;
}

/*
 *      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;

        if(!files)
                BUG();

        /* 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 inline 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);
        tsk->sighand = sig;
        if (!sig)
                return -ENOMEM;
        spin_lock_init(&sig->siglock);
        atomic_set(&sig->count, 1);
        memcpy(sig->action, current->sighand->action, sizeof(sig->action));
        return 0;
}

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

        if (clone_flags & CLONE_THREAD) {
                atomic_inc(&current->signal->count);
                return 0;
        }
        sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
        tsk->signal = sig;
        if (!sig)
                return -ENOMEM;
        atomic_set(&sig->count, 1);
        sig->group_exit = 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);

        sig->tty = current->signal->tty;
        sig->pgrp = process_group(current);
        sig->session = current->signal->session;
        sig->leader = 0;        /* session leadership doesn't inherit */
        sig->tty_old_pgrp = 0;

        sig->utime = sig->stime = sig->cutime = sig->cstime = 0;
        sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
        sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;

        return 0;
}

static inline 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;
}

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

        return current->pid;
}

/*
 * 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 task_t *copy_process(unsigned long clone_flags,
                                 unsigned long stack_start,
                                 struct pt_regs *regs,
                                 unsigned long stack_size,
                                 int __user *parent_tidptr,
                                 int __user *child_tidptr,
                                 int pid)
{
        int retval;
        struct task_struct *p = NULL;

        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;

        retval = -EAGAIN;
        if (atomic_read(&p->user->processes) >=
                        p->rlim[RLIMIT_NPROC].rlim_cur) {
                if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
                                p->user != &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(p->thread_info->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;
        copy_flags(clone_flags, p);
        p->pid = pid;
        retval = -EFAULT;
        if (clone_flags & CLONE_PARENT_SETTID)
                if (put_user(p->pid, parent_tidptr))
                        goto bad_fork_cleanup;

        p->proc_dentry = NULL;

        INIT_LIST_HEAD(&p->children);
        INIT_LIST_HEAD(&p->sibling);
        init_waitqueue_head(&p->wait_chldexit);
        p->vfork_done = NULL;
        spin_lock_init(&p->alloc_lock);
        spin_lock_init(&p->proc_lock);

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

        p->it_real_value = p->it_virt_value = p->it_prof_value = 0;
        p->it_real_incr = p->it_virt_incr = p->it_prof_incr = 0;
        init_timer(&p->real_timer);
        p->real_timer.data = (unsigned long) p;

        p->utime = p->stime = 0;
        p->lock_depth = -1;             /* -1 = no lock */
        do_posix_clock_monotonic_gettime(&p->start_time);
        p->security = NULL;
        p->io_context = NULL;
        p->io_wait = NULL;
        p->audit_context = NULL;
#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;
        }
#endif

        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_namespace(clone_flags, p)))
                goto bad_fork_cleanup_mm;
        retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
        if (retval)
                goto bad_fork_cleanup_namespace;

        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;

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

        /* 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;

        /* Perform scheduler related setup */
        sched_fork(p);

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

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

        /*
         * The task hasn't been attached yet, so cpus_allowed mask cannot
         * have changed. The cpus_allowed mask of the parent may have
         * changed after it was copied first time, and it may then move to
         * another CPU - so we re-copy it here and set the child's CPU to
         * the parent's CPU. This avoids alot of nasty races.
         */
        p->cpus_allowed = current->cpus_allowed;
        set_task_cpu(p, smp_processor_id());

        /*
         * Check for pending SIGKILL! The new thread should not be allowed
         * to slip out of an OOM kill. (or normal SIGKILL.)
         */
        if (sigismember(&current->pending.signal, SIGKILL)) {
                write_unlock_irq(&tasklist_lock);
                retval = -EINTR;
                goto bad_fork_cleanup_namespace;
        }

        /* 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;

        if (clone_flags & CLONE_THREAD) {
                spin_lock(&current->sighand->siglock);
                /*
                 * Important: if an exit-all has been started then
                 * do not create this new thread - the whole thread
                 * group is supposed to exit anyway.
                 */
                if (current->signal->group_exit) {
                        spin_unlock(&current->sighand->siglock);
                        write_unlock_irq(&tasklist_lock);
                        retval = -EAGAIN;
                        goto bad_fork_cleanup_namespace;
                }
                p->tgid = current->tgid;
                p->group_leader = current->group_leader;

                if (current->signal->group_stop_count > 0) {
                        /*
                         * There is an all-stop in progress for the group.
                         * We ourselves will stop as soon as we check signals.
                         * Make the new thread part of that group stop too.
                         */
                        current->signal->group_stop_count++;
                        set_tsk_thread_flag(p, TIF_SIGPENDING);
                }

                spin_unlock(&current->sighand->siglock);
        }

        SET_LINKS(p);
        if (unlikely(p->ptrace & PT_PTRACED))
                __ptrace_link(p, current->parent);

        attach_pid(p, PIDTYPE_PID, p->pid);
        attach_pid(p, PIDTYPE_TGID, p->tgid);
        if (thread_group_leader(p)) {
                attach_pid(p, PIDTYPE_PGID, process_group(p));
                attach_pid(p, PIDTYPE_SID, p->signal->session);
                if (p->pid)
                        __get_cpu_var(process_counts)++;
        }

        nr_threads++;
        write_unlock_irq(&tasklist_lock);
        retval = 0;

fork_out:
        if (retval)
                return ERR_PTR(retval);
        return p;

bad_fork_cleanup_namespace:
        exit_namespace(p);
bad_fork_cleanup_mm:
        if (p->mm)
                mmput(p->mm);
bad_fork_cleanup_signal:
        exit_signal(p);
bad_fork_cleanup_sighand:
        exit_sighand(p);
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);
#endif
bad_fork_cleanup:
        if (p->binfmt)
                module_put(p->binfmt->module);
bad_fork_cleanup_put_domain:
        module_put(p->thread_info->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);
        goto fork_out;
}

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

task_t * __devinit fork_idle(int cpu)
{
        task_t *task;
        struct pt_regs regs;

        task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL, NULL, 0);
        if (!task)
                return ERR_PTR(-ENOMEM);
        init_idle(task, cpu);
        unhash_process(task);
        return task;
}

static inline 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 pid = alloc_pidmap();

        if (pid < 0)
                return -EAGAIN;
        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, parent_tidptr, child_tidptr, pid);
        /*
         * 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;

                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;
                ++total_forks;

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

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

/* SLAB cache for signal_struct structures (tsk->signal) */
kmem_cache_t *signal_cachep;

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

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

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

/* SLAB cache for vm_area_struct structures */
kmem_cache_t *vm_area_cachep;

/* SLAB cache for mm_struct structures (tsk->mm) */
kmem_cache_t *mm_cachep;

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