From: Yu Kuai <yukuai3@huawei.com>

This reverts commit b13015af94cf405f73ff64ce0797269554020c37.

Because this will cause that r5c_disable_writeback_async() to wait
forever, since caller hold reconfig_mutex and conf->log is not NULL:

wait_event
 conf->log == NULL ||
 (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) &&
  (locked = mddev_trylock(mddev)))

This problem is found by code review, and the null-ptr-deref this patch
fixed will be fixed by another approch in the next patch.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/raid5-cache.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 47ba7d9e81e1..083288e36949 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -3168,13 +3168,12 @@ void r5l_exit_log(struct r5conf *conf)
 {
 	struct r5l_log *log = conf->log;
 
+	conf->log = NULL;
+
 	/* Ensure disable_writeback_work wakes up and exits */
 	wake_up(&conf->mddev->sb_wait);
 	flush_work(&log->disable_writeback_work);
 	md_unregister_thread(&log->reclaim_thread);
-
-	conf->log = NULL;
-
 	mempool_exit(&log->meta_pool);
 	bioset_exit(&log->bs);
 	mempool_exit(&log->io_pool);
-- 
2.39.2