path: root/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_tables()'
 */

#include <linux/config.h>
#include <linux/malloc.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/vmalloc.h>

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

/* The idle threads do not count.. */
int nr_threads;
int nr_running;

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

/* SLAB cache for mm_struct's. */
kmem_cache_t *mm_cachep;

struct task_struct *pidhash[PIDHASH_SZ];

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

	wq_write_lock_irqsave(&q->lock, flags);
	__add_wait_queue(q, wait);
	wq_write_unlock_irqrestore(&q->lock, flags);
}

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

	wq_write_lock_irqsave(&q->lock, flags);
	__add_wait_queue_tail(q, wait);
	wq_write_unlock_irqrestore(&q->lock, flags);
}

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

	wq_write_lock_irqsave(&q->lock, flags);
	__remove_wait_queue(q, wait);
	wq_write_unlock_irqrestore(&q->lock, flags);
}

void __init fork_init(unsigned long mempages)
{
	/*
	 * 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) / 2;

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

/* Protects next_safe and last_pid. */
spinlock_t lastpid_lock = SPIN_LOCK_UNLOCKED;

static int get_pid(unsigned long flags)
{
	static int next_safe = PID_MAX;
	struct task_struct *p;

	if (flags & CLONE_PID)
		return current->pid;

	spin_lock(&lastpid_lock);
	if((++last_pid) & 0xffff8000) {
		last_pid = 300;		/* Skip daemons etc. */
		goto inside;
	}
	if(last_pid >= next_safe) {
inside:
		next_safe = PID_MAX;
		read_lock(&tasklist_lock);
	repeat:
		for_each_task(p) {
			if(p->pid == last_pid	||
			   p->pgrp == last_pid	||
			   p->session == last_pid) {
				if(++last_pid >= next_safe) {
					if(last_pid & 0xffff8000)
						last_pid = 300;
					next_safe = PID_MAX;
				}
				goto repeat;
			}
			if(p->pid > last_pid && next_safe > p->pid)
				next_safe = p->pid;
			if(p->pgrp > last_pid && next_safe > p->pgrp)
				next_safe = p->pgrp;
			if(p->session > last_pid && next_safe > p->session)
				next_safe = p->session;
		}
		read_unlock(&tasklist_lock);
	}
	spin_unlock(&lastpid_lock);

	return last_pid;
}

static inline int dup_mmap(struct mm_struct * mm)
{
	struct vm_area_struct * mpnt, *tmp, **pprev;
	int retval;

	/* Kill me slowly. UGLY! FIXME! */
	memcpy(&mm->start_code, &current->mm->start_code, 15*sizeof(unsigned long));

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

		retval = -ENOMEM;
		if(mpnt->vm_flags & VM_DONTCOPY)
			continue;
		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;
		mm->map_count++;
		tmp->vm_next = NULL;
		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(&inode->i_mapping->i_shared_lock);
			if((tmp->vm_next_share = mpnt->vm_next_share) != NULL)
				mpnt->vm_next_share->vm_pprev_share =
					&tmp->vm_next_share;
			mpnt->vm_next_share = tmp;
			tmp->vm_pprev_share = &mpnt->vm_next_share;
			spin_unlock(&inode->i_mapping->i_shared_lock);
		}

		/* Copy the pages, but defer checking for errors */
		retval = copy_page_range(mm, current->mm, tmp);
		if (!retval && tmp->vm_ops && tmp->vm_ops->open)
			tmp->vm_ops->open(tmp);

		/*
		 * Link in the new vma even if an error occurred,
		 * so that exit_mmap() can clean up the mess.
		 */
		tmp->vm_next = *pprev;
		*pprev = tmp;

		pprev = &tmp->vm_next;
		if (retval)
			goto fail_nomem;
	}
	retval = 0;
	if (mm->map_count >= AVL_MIN_MAP_COUNT)
		build_mmap_avl(mm);

fail_nomem:
	flush_tlb_mm(current->mm);
	return retval;
}

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

	mm = kmem_cache_alloc(mm_cachep, SLAB_KERNEL);
	if (mm) {
		memset(mm, 0, sizeof(*mm));
		atomic_set(&mm->mm_users, 1);
		atomic_set(&mm->mm_count, 1);
		init_MUTEX(&mm->mmap_sem);
		mm->page_table_lock = SPIN_LOCK_UNLOCKED;
		mm->pgd = pgd_alloc();
		if (mm->pgd)
			return mm;
		kmem_cache_free(mm_cachep, 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)
{
	if (mm == &init_mm) BUG();
	pgd_free(mm->pgd);
	destroy_context(mm);
	kmem_cache_free(mm_cachep, mm);
}

/*
 * Decrement the use count and release all resources for an mm.
 */
void mmput(struct mm_struct *mm)
{
	if (atomic_dec_and_test(&mm->mm_users)) {
		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(void)
{
	struct task_struct *tsk = current;

	/* notify parent sleeping on vfork() */
	if (tsk->flags & PF_VFORK) {
		tsk->flags &= ~PF_VFORK;
		up(tsk->p_opptr->vfork_sem);
	}
}

static inline int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
	struct mm_struct * mm;
	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..
	 */
	mm = current->mm;
	if (!mm)
		return 0;

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

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

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

	/*
	 * child gets a private LDT (if there was an LDT in the parent)
	 */
	copy_segments(tsk, mm);

	down(&current->mm->mmap_sem);
	retval = dup_mmap(mm);
	up(&current->mm->mmap_sem);
	if (retval)
		goto free_pt;

good_mm:
	tsk->mm = mm;
	tsk->active_mm = mm;
	init_new_context(tsk,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 = kmalloc(sizeof(*old), 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);
		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);
		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)
{
	if (clone_flags & CLONE_SIGHAND) {
		atomic_inc(&current->sig->count);
		return 0;
	}
	tsk->sig = kmalloc(sizeof(*tsk->sig), GFP_KERNEL);
	if (!tsk->sig)
		return -1;
	spin_lock_init(&tsk->sig->siglock);
	atomic_set(&tsk->sig->count, 1);
	memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
	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 | PF_USEDFPU | PF_VFORK);
	new_flags |= PF_FORKNOEXEC;
	if (!(clone_flags & CLONE_PTRACE))
		p->ptrace = 0;
	if (clone_flags & CLONE_VFORK)
		new_flags |= PF_VFORK;
	p->flags = new_flags;
}

/*
 *  Ok, this is the main fork-routine. It copies the system process
 * information (task[nr]) and sets up the necessary registers. It
 * also copies the data segment in its entirety.
 */
int do_fork(unsigned long clone_flags, unsigned long usp, struct pt_regs *regs)
{
	int retval = -ENOMEM;
	struct task_struct *p;
	DECLARE_MUTEX_LOCKED(sem);

	if (clone_flags & CLONE_PID) {
		/* This is only allowed from the boot up thread */
		if (current->pid)
			return -EPERM;
	}
	
	current->vfork_sem = &sem;

	p = alloc_task_struct();
	if (!p)
		goto fork_out;

	*p = *current;

	lock_kernel();

	retval = -EAGAIN;
	if (atomic_read(&p->user->processes) >= p->rlim[RLIMIT_NPROC].rlim_cur)
		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 (p->exec_domain && p->exec_domain->module)
		__MOD_INC_USE_COUNT(p->exec_domain->module);
	if (p->binfmt && p->binfmt->module)
		__MOD_INC_USE_COUNT(p->binfmt->module);

	p->did_exec = 0;
	p->swappable = 0;
	p->state = TASK_UNINTERRUPTIBLE;

	copy_flags(clone_flags, p);
	p->pid = get_pid(clone_flags);

	p->run_list.next = NULL;
	p->run_list.prev = NULL;

	if ((clone_flags & CLONE_VFORK) || !(clone_flags & CLONE_PARENT)) {
		p->p_opptr = current;
		if (!(p->ptrace & PT_PTRACED))
			p->p_pptr = current;
	}
	p->p_cptr = NULL;
	init_waitqueue_head(&p->wait_chldexit);
	p->vfork_sem = NULL;
	spin_lock_init(&p->alloc_lock);

	p->sigpending = 0;
	sigemptyset(&p->signal);
	p->sigqueue = NULL;
	p->sigqueue_tail = &p->sigqueue;

	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->times.tms_utime = p->times.tms_stime = 0;
	p->times.tms_cutime = p->times.tms_cstime = 0;
#ifdef CONFIG_SMP
	{
		int i;
		p->has_cpu = 0;
		p->processor = current->processor;
		/* ?? should we just memset this ?? */
		for(i = 0; i < smp_num_cpus; i++)
			p->per_cpu_utime[i] = p->per_cpu_stime[i] = 0;
		spin_lock_init(&p->sigmask_lock);
	}
#endif
	p->lock_depth = -1;		/* -1 = no lock */
	p->start_time = jiffies;

	retval = -ENOMEM;
	/* copy all the process information */
	if (copy_files(clone_flags, p))
		goto bad_fork_cleanup;
	if (copy_fs(clone_flags, p))
		goto bad_fork_cleanup_files;
	if (copy_sighand(clone_flags, p))
		goto bad_fork_cleanup_fs;
	if (copy_mm(clone_flags, p))
		goto bad_fork_cleanup_sighand;
	retval = copy_thread(0, clone_flags, usp, p, regs);
	if (retval)
		goto bad_fork_cleanup_sighand;
	p->semundo = NULL;
	
	/* 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->swappable = 1;
	p->exit_signal = clone_flags & CSIGNAL;
	p->pdeath_signal = 0;

	/*
	 * "share" dynamic priority between parent and child, thus the
	 * total amount of dynamic priorities in the system doesnt change,
	 * more scheduling fairness. This is only important in the first
	 * timeslice, on the long run the scheduling behaviour is unchanged.
	 */
	p->counter = (current->counter + 1) >> 1;
	current->counter >>= 1;
	if (!current->counter)
		current->need_resched = 1;

	/*
	 * Ok, add it to the run-queues and make it
	 * visible to the rest of the system.
	 *
	 * Let it rip!
	 */
	retval = p->pid;
	write_lock_irq(&tasklist_lock);
	SET_LINKS(p);
	hash_pid(p);
	nr_threads++;
	write_unlock_irq(&tasklist_lock);

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

bad_fork:
	unlock_kernel();
fork_out:
	if ((clone_flags & CLONE_VFORK) && (retval > 0)) 
		down(&sem);
	return retval;

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:
	put_exec_domain(p->exec_domain);
	if (p->binfmt && p->binfmt->module)
		__MOD_DEC_USE_COUNT(p->binfmt->module);
bad_fork_cleanup_count:
	atomic_dec(&p->user->processes);
	free_uid(p->user);
bad_fork_free:
	free_task_struct(p);
	goto bad_fork;
}