[fuse] fix deadlock between fuse_put_super() and request_end(), try #2
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 solution is to move the fput() outside the region protected by
sbput_sem.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 4967bd4..104a62d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -128,12 +128,16 @@
}
}
+/*
+ * Called with sbput_sem held for read (request_end) or write
+ * (fuse_put_super). By the time fuse_put_super() is finished, all
+ * inodes belonging to background requests must be released, so the
+ * iputs have to be done within the locked region.
+ */
void fuse_release_background(struct fuse_conn *fc, struct fuse_req *req)
{
iput(req->inode);
iput(req->inode2);
- if (req->file)
- fput(req->file);
spin_lock(&fc->lock);
list_del(&req->bg_entry);
if (fc->num_background == FUSE_MAX_BACKGROUND) {
@@ -178,6 +182,11 @@
if (fc->mounted)
fuse_release_background(fc, req);
up_read(&fc->sbput_sem);
+
+ /* fput must go outside sbput_sem, otherwise it can deadlock */
+ if (req->file)
+ fput(req->file);
+
if (end)
end(fc, req);
else