Commit 8a301eb1 authored Feb 02, 2018 by Tejun Heo Committed by Miklos Szeredi May 31, 2018

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 26c36791 ("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>

parent 4ad769f3

fs/fuse/dev.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}

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