FAILED: patch "[PATCH] fuse: fix congested state leak on aborted connections" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Tejun Heo <[email protected]>
Date: Fri, 2 Feb 2018 09:54:14 -0800
Subject: [PATCH] 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.

index 686631f12001..e03ca14f40e9 100644
@@ -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);
 		}