[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>

1 files changed, 3 insertions, 9 deletions

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 19c7185a7546..ee9b83042510 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -255,15 +255,9 @@ struct fuse_conn {
 	/** waitq for blocked connection */
 	wait_queue_head_t blocked_waitq;
 
-	/** RW semaphore for exclusion with fuse_put_super() */
-	struct rw_semaphore sbput_sem;
-
 	/** The next unique request id */
 	u64 reqctr;
 
-	/** Mount is active */
-	unsigned mounted;
-
 	/** Connection established, cleared on umount, connection
 	    abort and device release */
 	unsigned connected;
@@ -474,11 +468,11 @@ void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req);
 void request_send_background(struct fuse_conn *fc, struct fuse_req *req);
 
 /**
- * Release inodes and file associated with background request
+ * Remove request from the the background list
  */
-void fuse_release_background(struct fuse_conn *fc, struct fuse_req *req);
+void fuse_remove_background(struct fuse_conn *fc, struct fuse_req *req);
 
-/* Abort all requests */
+/** Abort all requests */
 void fuse_abort_conn(struct fuse_conn *fc);
 
 /**