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/file.h>
#include <linux/binfmts.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/security.h>
#include <linux/jiffies.h>
#include <linux/futex.h>
#include <linux/ptrace.h>
#include <linux/mount.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>

static kmem_cache_t *task_struct_cachep;

extern int copy_semundo(unsigned long clone_flags, struct task_struct *tsk);
extern void exit_semundo(struct task_struct *tsk);

/* The idle threads do not count.. */
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 */

/*
 * A per-CPU task cache - this relies on the fact that
 * the very last portion of sys_exit() is executed with
 * preemption turned off.
 */
static task_t *task_cache[NR_CPUS] __cacheline_aligned;

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

	for (cpu = 0; cpu < NR_CPUS; cpu++) {
		if (cpu_online(cpu))
			total += per_cpu(process_counts, cpu);
	}
	return total;
}

void __put_task_struct(struct task_struct *tsk)
{
	if (tsk != current) {
		free_thread_info(tsk->thread_info);
		kmem_cache_free(task_struct_cachep,tsk);
	} else {
		int cpu = get_cpu();

		tsk = task_cache[cpu];
		if (tsk) {
			free_thread_info(tsk->thread_info);
			kmem_cache_free(task_struct_cachep,tsk);
		}
		task_cache[cpu] = current;
		put_cpu();
	}
}

void 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);
}

void 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);
}

void 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);
}

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

	__set_current_state(state);
	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
	spin_lock_irqsave(&q->lock, flags);
	if (list_empty(&wait->task_list))
		__add_wait_queue(q, wait);
	spin_unlock_irqrestore(&q->lock, flags);
}

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

	__set_current_state(state);
	wait->flags |= WQ_FLAG_EXCLUSIVE;
	spin_lock_irqsave(&q->lock, flags);
	if (list_empty(&wait->task_list))
		__add_wait_queue_tail(q, wait);
	spin_unlock_irqrestore(&q->lock, flags);
}

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

	__set_current_state(TASK_RUNNING);
	if (!list_empty(&wait->task_list)) {
		spin_lock_irqsave(&q->lock, flags);
		list_del_init(&wait->task_list);
		spin_unlock_irqrestore(&q->lock, flags);
	}
}

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

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

void __init fork_init(unsigned long mempages)
{
	/* create a slab on which task_structs can be allocated */
	task_struct_cachep =
		kmem_cache_create("task_struct",
				  sizeof(struct task_struct),0,
				  SLAB_HWCACHE_ALIGN, NULL, NULL);
	if (!task_struct_cachep)
		panic("fork_init(): cannot create task_struct SLAB cache");

	/*
	 * 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;
	int cpu = get_cpu();

	tsk = task_cache[cpu];
	task_cache[cpu] = NULL;
	put_cpu();
	if (!tsk) {
		ti = alloc_thread_info();
		if (!ti)
			return NULL;

		tsk = kmem_cache_alloc(task_struct_cachep, GFP_KERNEL);
		if (!tsk) {
			free_thread_info(ti);
			return NULL;
		}
	} else
		ti = tsk->thread_info;

	*ti = *orig->thread_info;
	*tsk = *orig;
	tsk->thread_info = ti;
	ti->task = tsk;
	atomic_set(&tsk->usage,1);
	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;
	int retval;
	unsigned long charge = 0;

	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 = TASK_UNMAPPED_BASE;
	mm->map_count = 0;
	mm->rss = 0;
	mm->cpu_vm_mask = 0;
	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)
			continue;
		if (mpnt->vm_flags & VM_ACCOUNT) {
			unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
			if (!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;
		tmp->vm_flags &= ~VM_LOCKED;
		tmp->vm_mm = mm;
		tmp->vm_next = NULL;
		file = tmp->vm_file;
		INIT_LIST_HEAD(&tmp->shared);
		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 */
			down(&inode->i_mapping->i_shared_sem);
			list_add_tail(&tmp->shared, &mpnt->shared);
			up(&inode->i_mapping->i_shared_sem);
		}

		/*
		 * Link in the new vma and copy the page table entries:
		 * link in first so that swapoff can see swap entries.
		 */
		spin_lock(&mm->page_table_lock);
		*pprev = tmp;
		pprev = &tmp->vm_next;
		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 fail;
	}
	retval = 0;
	build_mmap_rb(mm);

out:
	flush_tlb_mm(current->mm);
	up_write(&oldmm->mmap_sem);
	return retval;
fail_nomem:
	retval = -ENOMEM;
  fail:
	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->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));
		return mm_init(mm);
	}
	return NULL;
}

/*
 * 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.
 */
inline void __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);
		mmdrop(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) {
		int * tidptr = tsk->clear_child_tid;
		tsk->clear_child_tid = NULL;

		/*
		 * We dont check the error code - if userspace has
		 * not set up a proper pointer then tough luck.
		 */
		put_user(0, tidptr);
		sys_futex((unsigned long)tidptr, FUTEX_WAKE, 1, 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->cmin_flt = tsk->cmaj_flt = 0;
	tsk->nswap = tsk->cnswap = 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 free_pt;

	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;
}

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);
}

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 -1;
	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;
	}

	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	    = RW_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;
		write_lock(&newf->file_lock);
		error = expand_fdset(newf, size-1);
		write_unlock(&newf->file_lock);
		if (error)
			goto out_release;
	}
	read_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) {
		read_unlock(&oldf->file_lock);
		newf->max_fds = 0;
		write_lock(&newf->file_lock);
		error = expand_fd_array(newf, open_files-1);
		write_unlock(&newf->file_lock);
		if (error) 
			goto out_release;
		nfds = newf->max_fds;
		read_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;
	}
	read_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;
}

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 -1;
	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 -1;
	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);

	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 int sys_set_tid_address(int *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 struct task_struct *copy_process(unsigned long clone_flags,
			    unsigned long stack_start,
			    struct pt_regs *regs,
			    unsigned long stack_size,
			    int *parent_tidptr,
			    int *child_tidptr)
{
	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);
	if ((clone_flags & CLONE_DETACHED) && !(clone_flags & CLONE_THREAD))
		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))
			goto bad_fork_free;
	}

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

	/*
	 * Counter increases are protected by
	 * the kernel lock so nr_threads can't
	 * increase under us (but it may decrease).
	 */
	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;

#ifdef CONFIG_PREEMPT
	/*
	 * schedule_tail drops this_rq()->lock so we compensate with a count
	 * of 1.  Also, we want to start with kernel preemption disabled.
	 */
	p->thread_info->preempt_count = 1;
#endif
	p->did_exec = 0;
	p->state = TASK_UNINTERRUPTIBLE;

	copy_flags(clone_flags, p);
	if (clone_flags & CLONE_IDLETASK)
		p->pid = 0;
	else {
		p->pid = alloc_pidmap();
		if (p->pid == -1)
			goto bad_fork_cleanup;
	}
	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->run_list);

	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->switch_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->leader = 0;		/* session leadership doesn't inherit */
	p->tty_old_pgrp = 0;
	p->utime = p->stime = 0;
	p->cutime = p->cstime = 0;
	p->array = NULL;
	p->lock_depth = -1;		/* -1 = no lock */
	p->start_time = get_jiffies_64();
	p->security = NULL;

	retval = -ENOMEM;
	if (security_task_alloc(p))
		goto bad_fork_cleanup;
	/* copy all the process information */
	if (copy_semundo(clone_flags, p))
		goto bad_fork_cleanup_security;
	if (copy_files(clone_flags, p))
		goto bad_fork_cleanup_semundo;
	if (copy_fs(clone_flags, p))
		goto bad_fork_cleanup_files;
	if (copy_sighand(clone_flags, p))
		goto bad_fork_cleanup_fs;
	if (copy_signal(clone_flags, p))
		goto bad_fork_cleanup_sighand;
	if (copy_mm(clone_flags, p))
		goto bad_fork_cleanup_signal;
	if (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;

	if (clone_flags & CLONE_CHILD_SETTID)
		p->set_child_tid = child_tidptr;
	/*
	 * Clear TID on mm_release()?
	 */
	if (clone_flags & CLONE_CHILD_CLEARTID)
		p->clear_child_tid = child_tidptr;

	/*
	 * 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.. */
	if (clone_flags & CLONE_DETACHED)
		p->exit_signal = -1;
	else
		p->exit_signal = clone_flags & CSIGNAL;
	p->pdeath_signal = 0;

	/*
	 * Share the timeslice between parent and child, thus the
	 * total amount of pending timeslices in the system doesnt change,
	 * resulting in more scheduling fairness.
	 */
	local_irq_disable();
        p->time_slice = (current->time_slice + 1) >> 1;
	/*
	 * The remainder of the first timeslice might be recovered by
	 * the parent if the child exits early enough.
	 */
	p->first_time_slice = 1;
	current->time_slice >>= 1;
	p->sleep_timestamp = jiffies;
	if (!current->time_slice) {
		/*
	 	 * This case is rare, it happens when the parent has only
	 	 * a single jiffy left from its timeslice. Taking the
		 * runqueue lock is not a problem.
		 */
		current->time_slice = 1;
		preempt_disable();
		scheduler_tick(0, 0);
		local_irq_enable();
		preempt_enable();
	} else
		local_irq_enable();
	/*
	 * Ok, add it to the run-queues and make it
	 * visible to the rest of the system.
	 *
	 * Let it rip!
	 */
	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);
	/*
	 * 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)
		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);
			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 (p->ptrace & PT_PTRACED)
		__ptrace_link(p, current->parent);

	attach_pid(p, PIDTYPE_PID, p->pid);
	if (thread_group_leader(p)) {
		attach_pid(p, PIDTYPE_TGID, p->tgid);
		attach_pid(p, PIDTYPE_PGID, p->pgrp);
		attach_pid(p, PIDTYPE_SID, p->session);
		if (p->pid)
			per_cpu(process_counts, smp_processor_id())++;
	} else
		link_pid(p, p->pids + PIDTYPE_TGID, &p->group_leader->pids[PIDTYPE_TGID].pid);

	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:
	exit_mm(p);
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_semundo(p);
bad_fork_cleanup_security:
	security_task_free(p);
bad_fork_cleanup:
	if (p->pid > 0)
		free_pidmap(p->pid);
	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:
	atomic_dec(&p->user->processes);
	free_uid(p->user);
bad_fork_free:
	put_task_struct(p);
	goto fork_out;
}

static inline int fork_traceflag (unsigned clone_flags)
{
	if (clone_flags & (CLONE_UNTRACED | CLONE_IDLETASK))
		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.
 */
struct task_struct *do_fork(unsigned long clone_flags,
			    unsigned long stack_start,
			    struct pt_regs *regs,
			    unsigned long stack_size,
			    int *parent_tidptr,
			    int *child_tidptr)
{
	struct task_struct *p;
	int trace = 0;

	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);
	if (!IS_ERR(p)) {
		struct completion vfork;

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

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

		wake_up_forked_process(p);		/* do this last */
		++total_forks;

		if (unlikely (trace)) {
			current->ptrace_message = (unsigned long) p->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
			/*
			 * Let the child process run first, to avoid most of the
			 * COW overhead when the child exec()s afterwards.
			 */
			set_need_resched();
	}
	return p;
}

/* 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, NULL, NULL);
	if (!sighand_cachep)
		panic("Cannot create sighand SLAB cache");

	signal_cachep = kmem_cache_create("signal_cache",
			sizeof(struct signal_struct), 0,
			SLAB_HWCACHE_ALIGN, NULL, NULL);
	if (!signal_cachep)
		panic("Cannot create signal SLAB cache");

	files_cachep = kmem_cache_create("files_cache", 
			 sizeof(struct files_struct), 0, 
			 SLAB_HWCACHE_ALIGN, NULL, NULL);
	if (!files_cachep) 
		panic("Cannot create files SLAB cache");

	fs_cachep = kmem_cache_create("fs_cache", 
			 sizeof(struct fs_struct), 0, 
			 SLAB_HWCACHE_ALIGN, NULL, NULL);
	if (!fs_cachep) 
		panic("Cannot create fs_struct SLAB cache");
 
	vm_area_cachep = kmem_cache_create("vm_area_struct",
			sizeof(struct vm_area_struct), 0,
			0, NULL, NULL);
	if(!vm_area_cachep)
		panic("vma_init: Cannot alloc vm_area_struct SLAB cache");

	mm_cachep = kmem_cache_create("mm_struct",
			sizeof(struct mm_struct), 0,
			SLAB_HWCACHE_ALIGN, NULL, NULL);
	if(!mm_cachep)
		panic("vma_init: Cannot alloc mm_struct SLAB cache");
}