fuse: add missing FR_FORCE

fuse_file_put() was missing the "force" flag for the RELEASE request when
sending synchronously (fuseblk).

If this flag is not set, then a sync request may be interrupted before it
is dequeued by the userspace filesystem.  In this case the OPEN won't be
balanced with a RELEASE.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 5a18ec17 ("fuse: fix hang of single threaded fuseblk filesystem")
Cc: <stable@vger.kernel.org> # v2.6.38+

fs/fuse/file.c

@@ -100,6 +100,7 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
 			iput(req->misc.release.inode);
 			fuse_put_request(ff->fc, req);
 		} else if (sync) {
+			__set_bit(FR_FORCE, &req->flags);
 			__clear_bit(FR_BACKGROUND, &req->flags);
 			fuse_request_send(ff->fc, req);
 			iput(req->misc.release.inode);