fuse: fix congested state leak on aborted connections

If a connection gets aborted while congested, FUSE can leave
nr_wb_congested[] stuck until reboot causing wait_iff_congested() to
wait spuriously which can lead to severe performance degradation.

The leak is caused by gating congestion state clearing with
fc->connected test in request_end().  This was added way back in 2009
by 26c3679101db ("fuse: destroy bdi on umount").  While the commit
description doesn't explain why the test was added, it most likely was
to avoid dereferencing bdi after it got destroyed.

Since then, bdi lifetime rules have changed many times and now we're
always guaranteed to have access to the bdi while the superblock is
alive (fc->sb).

Drop fc->connected conditional to avoid leaking congestion states.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Joshua Miller <joshmiller@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: stable@vger.kernel.org # v2.6.29+
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 686631f12001c407c50c1b820e7719f1c5af370a..e03ca14f40e957703ad901e83c2f6ec90f46fc56 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -385,8 +385,7 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
                if (!fc->blocked && waitqueue_active(&fc->blocked_waitq))
                        wake_up(&fc->blocked_waitq);
 
-               if (fc->num_background == fc->congestion_threshold &&
-                   fc->connected && fc->sb) {
+               if (fc->num_background == fc->congestion_threshold && fc->sb) {
                        clear_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);
                        clear_bdi_congested(fc->sb->s_bdi, BLK_RW_ASYNC);
                }