[PATCH] blk-cgroup: clear blkg->pd[] with WRITE_ONCE() in blkcg_deactivate_policy()

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>

blkcg_activate_policy() installs blkg->pd[] entries with WRITE_ONCE()
and also uses WRITE_ONCE() when clearing them on its error path.
blkg_to_pd() is used by RCU readers and reads the same array with
READ_ONCE().

blkcg_deactivate_policy() clears the entry with a plain store. Use
WRITE_ONCE() there as well.

Fixes: 56cc24f59c14 ("blk-cgroup: don't nest queue_lock under rcu in blkcg_print_blkgs()")
Signed-off-by: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>
---
 block/blk-cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index d2a1f5903f24..a1dd69f99f5c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1691,7 +1691,7 @@ void blkcg_deactivate_policy(struct gendisk *disk,
 			if (blkg->pd[pol->plid]->online && pol->pd_offline_fn)
 				pol->pd_offline_fn(blkg->pd[pol->plid]);
 			pol->pd_free_fn(blkg->pd[pol->plid]);
-			blkg->pd[pol->plid] = NULL;
+			WRITE_ONCE(blkg->pd[pol->plid], NULL);
 		}
 		spin_unlock(&blkcg->lock);
 	}
-- 
2.43.0