[fuse] fix deadlock between fuse_put_super() and request_end()
A deadlock was possible, when the last reference to the superblock was
held due to a background request containing a file reference.
Releasing the file would release the vfsmount which in turn would
release the superblock. Since sbput_sem is held during the fput() and
fuse_put_super() tries to acquire this same semaphore, a deadlock
results.
The chosen soltuion is to get rid of sbput_sem, and instead use the
spinlock to ensure the referenced inodes/file are released only once.
Since the actual release may sleep, defer these outside the locked
region, but using local variables instead of the structure members.
This is a much more rubust solution.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index fd34037..43a6fc0 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -204,17 +204,26 @@
{
struct fuse_conn *fc = get_fuse_conn_super(sb);
- down_write(&fc->sbput_sem);
- while (!list_empty(&fc->background))
- fuse_release_background(fc,
- list_entry(fc->background.next,
- struct fuse_req, bg_entry));
-
spin_lock(&fc->lock);
- fc->mounted = 0;
fc->connected = 0;
+ while (!list_empty(&fc->background)) {
+ struct fuse_req *req = list_entry(fc->background.next,
+ struct fuse_req, bg_entry);
+ struct inode *inode = req->inode;
+ struct inode *inode2 = req->inode2;
+
+ /* File would hold a reference to vfsmount */
+ BUG_ON(req->file);
+ req->inode = NULL;
+ req->inode2 = NULL;
+ fuse_remove_background(fc, req);
+
+ spin_unlock(&fc->lock);
+ iput(inode);
+ iput(inode2);
+ spin_lock(&fc->lock);
+ }
spin_unlock(&fc->lock);
- up_write(&fc->sbput_sem);
/* Flush all readers on this fs */
kill_fasync(&fc->fasync, SIGIO, POLL_IN);
wake_up_all(&fc->waitq);
@@ -386,7 +395,6 @@
INIT_LIST_HEAD(&fc->processing);
INIT_LIST_HEAD(&fc->io);
INIT_LIST_HEAD(&fc->background);
- init_rwsem(&fc->sbput_sem);
kobj_set_kset_s(fc, connections_subsys);
kobject_init(&fc->kobj);
atomic_set(&fc->num_waiting, 0);
@@ -541,7 +549,6 @@
goto err_free_req;
sb->s_root = root_dentry;
- fc->mounted = 1;
fc->connected = 1;
kobject_get(&fc->kobj);
file->private_data = fc;