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Commit ff8e210a authored by David Howells's avatar David Howells Committed by Linus Torvalds
Browse files

AFS: fix file locking 



Fix file locking for AFS:

 (*) Start the lock manager thread under a mutex to avoid a race.

 (*) Made the locking non-fair: New readlocks will jump pending writelocks if
     there's a readlock currently granted on a file.  This makes the behaviour
     similar to Linux's VFS locking.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b34bd06e

fs/afs/flock.c

+79 −47
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl); 
static void afs_fl_release_private(struct file_lock *fl);



static struct workqueue_struct *afs_lock_manager;

static DEFINE_MUTEX(afs_lock_manager_mutex);



static struct file_lock_operations afs_lock_ops = {

	.fl_copy_lock		= afs_fl_copy_lock,
@@ -30,12 +31,20 @@ static struct file_lock_operations afs_lock_ops = { 
 */

static int afs_init_lock_manager(void)

{

	int ret;



	ret = 0;

	if (!afs_lock_manager) {

		afs_lock_manager = create_singlethread_workqueue("kafs_lockd");

		mutex_lock(&afs_lock_manager_mutex);

		if (!afs_lock_manager) {

			afs_lock_manager =

				create_singlethread_workqueue("kafs_lockd");

			if (!afs_lock_manager)

			return -ENOMEM;

				ret = -ENOMEM;

		}

	return 0;

		mutex_unlock(&afs_lock_manager_mutex);

	}

	return ret;

}



/*
@@ -67,6 +76,29 @@ static void afs_schedule_lock_extension(struct afs_vnode *vnode) 
			   AFS_LOCKWAIT * HZ / 2);

}



/*

 * grant one or more locks (readlocks are allowed to jump the queue if the

 * first lock in the queue is itself a readlock)

 * - the caller must hold the vnode lock

 */

static void afs_grant_locks(struct afs_vnode *vnode, struct file_lock *fl)

{

	struct file_lock *p, *_p;



	list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);

	if (fl->fl_type == F_RDLCK) {

		list_for_each_entry_safe(p, _p, &vnode->pending_locks,

					 fl_u.afs.link) {

			if (p->fl_type == F_RDLCK) {

				p->fl_u.afs.state = AFS_LOCK_GRANTED;

				list_move_tail(&p->fl_u.afs.link,

					       &vnode->granted_locks);

				wake_up(&p->fl_wait);

			}

		}

	}

}



/*

 * do work for a lock, including:

 * - probing for a lock we're waiting on but didn't get immediately
@@ -172,8 +204,7 @@ void afs_lock_work(struct work_struct *work) 
				       struct file_lock, fl_u.afs.link) == fl) {

				fl->fl_u.afs.state = ret;

				if (ret == AFS_LOCK_GRANTED)

					list_move_tail(&fl->fl_u.afs.link,

						       &vnode->granted_locks);

					afs_grant_locks(vnode, fl);

				else

					list_del_init(&fl->fl_u.afs.link);

				wake_up(&fl->fl_wait);
@@ -258,10 +289,23 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl) 


	spin_lock(&vnode->lock);



	if (list_empty(&vnode->pending_locks)) {

		/* if there's no-one else with a lock on this vnode, then we

		 * need to ask the server for a lock */

		if (list_empty(&vnode->granted_locks)) {

	/* if we've already got a readlock on the server then we can instantly

	 * grant another readlock, irrespective of whether there are any

	 * pending writelocks */

	if (type == AFS_LOCK_READ &&

	    vnode->flags & (1 << AFS_VNODE_READLOCKED)) {

		_debug("instant readlock");

		ASSERTCMP(vnode->flags &

			  ((1 << AFS_VNODE_LOCKING) |

			   (1 << AFS_VNODE_WRITELOCKED)), ==, 0);

		ASSERT(!list_empty(&vnode->granted_locks));

		goto sharing_existing_lock;

	}



	/* if there's no-one else with a lock on this vnode, then we need to

	 * ask the server for a lock */

	if (list_empty(&vnode->pending_locks) &&

	    list_empty(&vnode->granted_locks)) {

		_debug("not locked");

		ASSERTCMP(vnode->flags &

			  ((1 << AFS_VNODE_LOCKING) |
@@ -275,8 +319,10 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl) 
		clear_bit(AFS_VNODE_LOCKING, &vnode->flags);

		switch (ret) {

		case 0:

			_debug("acquired");

			goto acquired_server_lock;

		case -EWOULDBLOCK:

			_debug("would block");

			spin_lock(&vnode->lock);

			ASSERT(list_empty(&vnode->granted_locks));

			ASSERTCMP(vnode->pending_locks.next, ==,
@@ -290,20 +336,6 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl) 
		}

	}



		/* if we've already got a readlock on the server and no waiting

		 * writelocks, then we might be able to instantly grant another

		 * readlock */

		if (type == AFS_LOCK_READ &&

		    vnode->flags & (1 << AFS_VNODE_READLOCKED)) {

			_debug("instant readlock");

			ASSERTCMP(vnode->flags &

				  ((1 << AFS_VNODE_LOCKING) |

				   (1 << AFS_VNODE_WRITELOCKED)), ==, 0);

			ASSERT(!list_empty(&vnode->granted_locks));

			goto sharing_existing_lock;

		}

	}



	/* otherwise, we need to wait for a local lock to become available */

	_debug("wait local");

	list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);