locks.c

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 * Wake up processes that are blocked waiting for this lock,
 * notify the FS that the lock has been cleared and
 * finally free the lock.
 */
static inline void _delete_lock(struct file_lock *fl, unsigned int wait)
{
	fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
	if (fl->fl_fasync != NULL){
		printk(KERN_ERR "locks_delete_lock: fasync == %p\n", fl->fl_fasync);
		fl->fl_fasync = NULL;
	}

	if (fl->fl_remove)
		fl->fl_remove(fl);

	locks_wake_up_blocks(fl, wait);
	locks_free_lock(fl);
}

/*
 * Delete a lock and then free it.
 */
static void locks_delete_lock(struct file_lock **thisfl_p, unsigned int wait)
{
	struct file_lock *fl = *thisfl_p;

	_unhash_lock(thisfl_p);
	_delete_lock(fl, wait);
}

/*
 * Call back client filesystem in order to get it to unregister a lock,
 * then delete lock. Essentially useful only in locks_remove_*().
 * Note: this must be called with the semaphore already held!
 */
static inline void locks_unlock_delete(struct file_lock **thisfl_p)
{
	struct file_lock *fl = *thisfl_p;
	int (*lock)(struct file *, int, struct file_lock *);

	_unhash_lock(thisfl_p);
	if (fl->fl_file->f_op &&
	    (lock = fl->fl_file->f_op->lock) != NULL) {
		fl->fl_type = F_UNLCK;
		lock(fl->fl_file, F_SETLK, fl);
	}
	_delete_lock(fl, 0);
}

/* Determine if lock sys_fl blocks lock caller_fl. Common functionality
 * checks for shared/exclusive status of overlapping locks.
 */
static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
	switch (caller_fl->fl_type) {
	case F_RDLCK:
		return (sys_fl->fl_type == F_WRLCK);

	case F_WRLCK:
		return (1);

	default:
		printk(KERN_ERR "locks_conflict(): impossible lock type - %d\n",
		       caller_fl->fl_type);
		break;
	}
	return (0);	/* This should never happen */
}

/* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
 * checking before calling the locks_conflict().
 */
static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
	/* POSIX locks owned by the same process do not conflict with
	 * each other.
	 */
	if (!(sys_fl->fl_flags & FL_POSIX) ||
	    locks_same_owner(caller_fl, sys_fl))
		return (0);

	/* Check whether they overlap */
	if (!locks_overlap(caller_fl, sys_fl))
		return 0;

	return (locks_conflict(caller_fl, sys_fl));
}

/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
 * checking before calling the locks_conflict().
 */
static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
	/* FLOCK locks referring to the same filp do not conflict with
	 * each other.
	 */
	if (!(sys_fl->fl_flags & FL_FLOCK) ||
	    (caller_fl->fl_file == sys_fl->fl_file))
		return (0);
#ifdef MSNFS
	if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
		return 0;
#endif

	return (locks_conflict(caller_fl, sys_fl));
}

static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout)
{
	int result = 0;
	DECLARE_WAITQUEUE(wait, current);

	current->state = TASK_INTERRUPTIBLE;
	add_wait_queue(fl_wait, &wait);
	if (timeout == 0)
		schedule();
	else
		result = schedule_timeout(timeout);
	if (signal_pending(current))
		result = -ERESTARTSYS;
	remove_wait_queue(fl_wait, &wait);
	current->state = TASK_RUNNING;
	return result;
}

static int locks_block_on(struct file_lock *blocker, struct file_lock *waiter)
{
	int result;
	locks_insert_block(blocker, waiter);
	result = interruptible_sleep_on_locked(&waiter->fl_wait, 0);
	locks_delete_block(waiter);
	return result;
}

static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time)
{
	int result;
	locks_insert_block(blocker, waiter);
	result = interruptible_sleep_on_locked(&waiter->fl_wait, time);
	locks_delete_block(waiter);
	return result;
}

struct file_lock *
posix_test_lock(struct file *filp, struct file_lock *fl)
{
	struct file_lock *cfl;

	lock_kernel();
	for (cfl = filp->f_dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
		if (!(cfl->fl_flags & FL_POSIX))
			continue;
		if (posix_locks_conflict(cfl, fl))
			break;
	}
	unlock_kernel();

	return (cfl);
}

/* This function tests for deadlock condition before putting a process to
 * sleep. The detection scheme is no longer recursive. Recursive was neat,
 * but dangerous - we risked stack corruption if the lock data was bad, or
 * if the recursion was too deep for any other reason.
 *
 * We rely on the fact that a task can only be on one lock's wait queue
 * at a time. When we find blocked_task on a wait queue we can re-search
 * with blocked_task equal to that queue's owner, until either blocked_task
 * isn't found, or blocked_task is found on a queue owned by my_task.
 *
 * Note: the above assumption may not be true when handling lock requests
 * from a broken NFS client. But broken NFS clients have a lot more to
 * worry about than proper deadlock detection anyway... --okir
 */
int posix_locks_deadlock(struct file_lock *caller_fl,
				struct file_lock *block_fl)
{
	struct list_head *tmp;
	fl_owner_t caller_owner, blocked_owner;
	unsigned int	 caller_pid, blocked_pid;

	caller_owner = caller_fl->fl_owner;
	caller_pid = caller_fl->fl_pid;
	blocked_owner = block_fl->fl_owner;
	blocked_pid = block_fl->fl_pid;

next_task:
	if (caller_owner == blocked_owner && caller_pid == blocked_pid)
		return 1;
	list_for_each(tmp, &blocked_list) {
		struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
		if ((fl->fl_owner == blocked_owner)
		    && (fl->fl_pid == blocked_pid)) {
			fl = fl->fl_next;
			blocked_owner = fl->fl_owner;
			blocked_pid = fl->fl_pid;
			goto next_task;
		}
	}
	return 0;
}

int locks_mandatory_locked(struct inode *inode)
{
	fl_owner_t owner = current->files;
	struct file_lock *fl;

	/*
	 * Search the lock list for this inode for any POSIX locks.
	 */
	lock_kernel();
	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
		if (!(fl->fl_flags & FL_POSIX))
			continue;
		if (fl->fl_owner != owner)
			break;
	}
	unlock_kernel();
	return fl ? -EAGAIN : 0;
}

int locks_mandatory_area(int read_write, struct inode *inode,
			 struct file *filp, loff_t offset,
			 size_t count)
{
	struct file_lock *fl;
	struct file_lock *new_fl = locks_alloc_lock(0);
	int error;

	if (new_fl == NULL)
		return -ENOMEM;

	new_fl->fl_owner = current->files;
	new_fl->fl_pid = current->pid;
	new_fl->fl_file = filp;
	new_fl->fl_flags = FL_POSIX | FL_ACCESS;
	new_fl->fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
	new_fl->fl_start = offset;
	new_fl->fl_end = offset + count - 1;

	error = 0;
	lock_kernel();

repeat:
	/* Search the lock list for this inode for locks that conflict with
	 * the proposed read/write.
	 */
	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
		if (!(fl->fl_flags & FL_POSIX))
			continue;
		if (fl->fl_start > new_fl->fl_end)
			break;
		if (posix_locks_conflict(new_fl, fl)) {
			error = -EAGAIN;
			if (filp && (filp->f_flags & O_NONBLOCK))
				break;
			error = -EDEADLK;
			if (posix_locks_deadlock(new_fl, fl))
				break;
	
			error = locks_block_on(fl, new_fl);
			if (error != 0)
				break;
	
			/*
			 * If we've been sleeping someone might have
			 * changed the permissions behind our back.
			 */
			if ((inode->i_mode & (S_ISGID | S_IXGRP)) != S_ISGID)
				break;
			goto repeat;
		}
	}
	locks_free_lock(new_fl);
	unlock_kernel();
	return error;
}

/* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
 * at the head of the list, but that's secret knowledge known only to
 * flock_lock_file and posix_lock_file.
 */
static int flock_lock_file(struct file *filp, unsigned int lock_type,
			   unsigned int wait)
{
	struct file_lock *fl;
	struct file_lock *new_fl = NULL;
	struct file_lock **before;
	struct inode * inode = filp->f_dentry->d_inode;
	int error, change;
	int unlock = (lock_type == F_UNLCK);

	/*
	 * If we need a new lock, get it in advance to avoid races.
	 */
	if (!unlock) {
		error = -ENOLCK;
		new_fl = flock_make_lock(filp, lock_type);
		if (!new_fl)
			return error;
	}

	error = 0;
search:
	change = 0;
	before = &inode->i_flock;
	while (((fl = *before) != NULL) && (fl->fl_flags & FL_FLOCK)) {
		if (filp == fl->fl_file) {
			if (lock_type == fl->fl_type)
				goto out;
			change = 1;
			break;
		}
		before = &fl->fl_next;
	}
	/* change means that we are changing the type of an existing lock,
	 * or else unlocking it.
	 */
	if (change) {
		/* N.B. What if the wait argument is false? */
		locks_delete_lock(before, !unlock);
		/*
		 * If we waited, another lock may have been added ...
		 */
		if (!unlock)
			goto search;
	}
	if (unlock)
		goto out;

repeat:
	for (fl = inode->i_flock; (fl != NULL) && (fl->fl_flags & FL_FLOCK);
	     fl = fl->fl_next) {
		if (!flock_locks_conflict(new_fl, fl))
			continue;
		error = -EAGAIN;
		if (!wait)
			goto out;
		error = locks_block_on(fl, new_fl);
		if (error != 0)
			goto out;
		goto repeat;
	}
	locks_insert_lock(&inode->i_flock, new_fl);
	new_fl = NULL;
	error = 0;

out:
	if (new_fl)
		locks_free_lock(new_fl);
	return error;
}

/**
 *	posix_lock_file:
 *	@filp: The file to apply the lock to
 *	@caller: The lock to be applied
 *	@wait: 1 to retry automatically, 0 to return -EAGAIN
 *
 * Add a POSIX style lock to a file.
 * We merge adjacent locks whenever possible. POSIX locks are sorted by owner
 * task, then by starting address
 *
 * Kai Petzke writes:
 * To make freeing a lock much faster, we keep a pointer to the lock before the
 * actual one. But the real gain of the new coding was, that lock_it() and
 * unlock_it() became one function.
 *
 * To all purists: Yes, I use a few goto's. Just pass on to the next function.
 */

int posix_lock_file(struct file *filp, struct file_lock *caller,
			   unsigned int wait)
{
	struct file_lock *fl;
	struct file_lock *new_fl, *new_fl2;
	struct file_lock *left = NULL;
	struct file_lock *right = NULL;
	struct file_lock **before;
	struct inode * inode = filp->f_dentry->d_inode;
	int error, added = 0;

	/*
	 * We may need two file_lock structures for this operation,
	 * so we get them in advance to avoid races.
	 */
	new_fl = locks_alloc_lock(0);
	new_fl2 = locks_alloc_lock(0);
	error = -ENOLCK; /* "no luck" */
	if (!(new_fl && new_fl2))
		goto out_nolock;

	lock_kernel();
	if (caller->fl_type != F_UNLCK) {
  repeat:
		for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
			if (!(fl->fl_flags & FL_POSIX))
				continue;
			if (!posix_locks_conflict(caller, fl))
				continue;
			error = -EAGAIN;
			if (!wait)
				goto out;
			error = -EDEADLK;
			if (posix_locks_deadlock(caller, fl))
				goto out;

			error = locks_block_on(fl, caller);
			if (error != 0)
				goto out;
			goto repeat;
  		}
  	}

	/*
	 * We've allocated the new locks in advance, so there are no
	 * errors possible (and no blocking operations) from here on.
	 * 
	 * Find the first old lock with the same owner as the new lock.
	 */
	
	before = &inode->i_flock;

	/* First skip locks owned by other processes.
	 */
	while ((fl = *before) && (!(fl->fl_flags & FL_POSIX) ||
				  !locks_same_owner(caller, fl))) {
		before = &fl->fl_next;
	}

	/* Process locks with this owner.
	 */
	while ((fl = *before) && locks_same_owner(caller, fl)) {
		/* Detect adjacent or overlapping regions (if same lock type)
		 */
		if (caller->fl_type == fl->fl_type) {
			if (fl->fl_end < caller->fl_start - 1)
				goto next_lock;
			/* If the next lock in the list has entirely bigger
			 * addresses than the new one, insert the lock here.
			 */
			if (fl->fl_start > caller->fl_end + 1)
				break;

			/* If we come here, the new and old lock are of the
			 * same type and adjacent or overlapping. Make one
			 * lock yielding from the lower start address of both
			 * locks to the higher end address.
			 */
			if (fl->fl_start > caller->fl_start)
				fl->fl_start = caller->fl_start;
			else
				caller->fl_start = fl->fl_start;
			if (fl->fl_end < caller->fl_end)
				fl->fl_end = caller->fl_end;
			else
				caller->fl_end = fl->fl_end;
			if (added) {
				locks_delete_lock(before, 0);
				continue;
			}
			caller = fl;
			added = 1;
		}
		else {
			/* Processing for different lock types is a bit
			 * more complex.
			 */
			if (fl->fl_end < caller->fl_start)
				goto next_lock;
			if (fl->fl_start > caller->fl_end)
				break;
			if (caller->fl_type == F_UNLCK)
				added = 1;
			if (fl->fl_start < caller->fl_start)
				left = fl;
			/* If the next lock in the list has a higher end
			 * address than the new one, insert the new one here.
			 */
			if (fl->fl_end > caller->fl_end) {
				right = fl;
				break;
			}
			if (fl->fl_start >= caller->fl_start) {
				/* The new lock completely replaces an old
				 * one (This may happen several times).
				 */
				if (added) {