From 8a301eb16d99983a4961f884690ec97b92e7dcfe Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Fri, 2 Feb 2018 09:54:14 -0800
Subject: [PATCH] fuse: fix congested state leak on aborted connections
Git-commit: 8a301eb16d99983a4961f884690ec97b92e7dcfe
Patch-mainline: v4.18-rc1
References: bsc#1051510

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 fs/fuse/dev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 686631f12001..e03ca14f40e9 100644
--- 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);
 		}
-- 
2.18.0