[PATCH 4.9 59/63] bcache: release dc->writeback_lock properly in bch_writeback_thread()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shan Hai <shan.hai@oracle.com>

commit 3943b040f11ed0cc6d4585fd286a623ca8634547 upstream.

The writeback thread would exit with a lock held when the cache device
is detached via sysfs interface, fix it by releasing the held lock
before exiting the while-loop.

Fixes: fadd94e05c02 (bcache: quit dc->writeback_thread when BCACHE_DEV_DETACHING is set)
Signed-off-by: Shan Hai <shan.hai@oracle.com>
Signed-off-by: Coly Li <colyli@suse.de>
Tested-by: Shenghui Wang <shhuiw@foxmail.com>
Cc: stable@vger.kernel.org #4.17+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/bcache/writeback.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -456,8 +456,10 @@ static int bch_writeback_thread(void *ar
 			 * data on cache. BCACHE_DEV_DETACHING flag is set in
 			 * bch_cached_dev_detach().
 			 */
-			if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
+			if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
+				up_write(&dc->writeback_lock);
 				break;
+			}
 		}
 
 		up_write(&dc->writeback_lock);