[PATCH] block,iocost: fix potential kernel NULL

[Yahu Gao <gaoyahu19@gmail.com>]

From: Yahu Gao <yahugao@didiglobal.com>

Some inode pinned dying memory cgroup and its parent destroyed at first.
The parent's pd of iocost won't be allocated during function
blkcg_activate_policy.
Ignore the DYING CSS to avoid kernel NULL during iocost policy data init.

Signed-off-by: Yahu Gao <yahugao@didiglobal.com>
Signed-off-by: Kunhai Dai <daikunhai@didiglobal.com>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index a91f8ae18b49..32472de2e61d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1418,6 +1418,9 @@ int blkcg_activate_policy(struct request_queue *q,
 	list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
 		struct blkg_policy_data *pd;
 
+		if (blkg->blkcg->css.flags & CSS_DYING)
+			continue;
+
 		if (blkg->pd[pol->plid])
 			continue;
 
@@ -1459,8 +1462,11 @@ int blkcg_activate_policy(struct request_queue *q,
 
 	/* all allocated, init in the same order */
 	if (pol->pd_init_fn)
-		list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
+		list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
+			if (blkg->blkcg->css.flags & CSS_DYING)
+				continue;
 			pol->pd_init_fn(blkg->pd[pol->plid]);
+		}
 
 	__set_bit(pol->plid, q->blkcg_pols);
 	ret = 0;
-- 
2.30.1