afs: Fix lock-wait/callback-break double locking

__afs_break_callback() holds vnode->lock around its call of
afs_lock_may_be_available() - which also takes that lock.

Fix this by not taking the lock in __afs_break_callback().

Also, there's no point checking the granted_locks and pending_locks queues;
it's sufficient to check lock_state, so move that check out of
afs_lock_may_be_available() into __afs_break_callback() to replace the
queue checks.

Fixes: e8d6c554 ("AFS: implement file locking")
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/callback.c

@@ -218,14 +218,8 @@ void __afs_break_callback(struct afs_vnode *vnode)
 		vnode->cb_break++;
 		afs_clear_permits(vnode);
 
-		spin_lock(&vnode->lock);
-
-		_debug("break callback");
-
-		if (list_empty(&vnode->granted_locks) &&
-		    !list_empty(&vnode->pending_locks))
+		if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
 			afs_lock_may_be_available(vnode);
-		spin_unlock(&vnode->lock);
 	}
 }
 

fs/afs/flock.c

@@ -41,9 +41,6 @@ void afs_lock_may_be_available(struct afs_vnode *vnode)
 {
 	_enter("{%llx:%llu}", vnode->fid.vid, vnode->fid.vnode);
 
-	if (vnode->lock_state != AFS_VNODE_LOCK_WAITING_FOR_CB)
-		return;
-
 	spin_lock(&vnode->lock);
 	if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
 		afs_next_locker(vnode, 0);