FAILED: patch "[PATCH] bcache: destroy dc->writeback_write_wq if failed to create" failed to apply to 4.9-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.9-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 <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

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

>From f54d801dda14942dbefa00541d10603015b7859c Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@xxxxxxx>
Date: Fri, 28 Jun 2019 19:59:44 +0800
Subject: [PATCH] bcache: destroy dc->writeback_write_wq if failed to create
 dc->writeback_thread

Commit 9baf30972b55 ("bcache: fix for gc and write-back race") added a
new work queue dc->writeback_write_wq, but forgot to destroy it in the
error condition when creating dc->writeback_thread failed.

This patch destroys dc->writeback_write_wq if kthread_create() returns
error pointer to dc->writeback_thread, then a memory leak is avoided.

Fixes: 9baf30972b55 ("bcache: fix for gc and write-back race")
Signed-off-by: Coly Li <colyli@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 262f7ef20992..21081febcb59 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -833,6 +833,7 @@ int bch_cached_dev_writeback_start(struct cached_dev *dc)
 					      "bcache_writeback");
 	if (IS_ERR(dc->writeback_thread)) {
 		cached_dev_put(dc);
+		destroy_workqueue(dc->writeback_write_wq);
 		return PTR_ERR(dc->writeback_thread);
 	}
 	dc->writeback_running = true;