From: Ming Lei <ming.lei@redhat.com>
Date: Tue, 19 Dec 2023 09:28:33 +0800
Subject: blk-cgroup: fix rcu lockdep warning in blkg_lookup()
Git-commit: 393cd8ffd832f23eec3a105553eff622e8198918
Patch-mainline: v6.7 or v6.7-rc9 (next release)
References: bsc#1218870

blkg_lookup() is called with either queue_lock or rcu read lock, so
use rcu_dereference_check(lockdep_is_held(&q->queue_lock)) for
retrieving 'blkg', which way models the check exactly for covering
queue lock or rcu read lock.

Fix lockdep warning of "block/blk-cgroup.h:254 suspicious rcu_dereference_check() usage!"
from blkg_lookup().

Tested-by: Changhui Zhong <czhong@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Fixes: 83462a6c971c ("blkcg: Drop unnecessary RCU read [un]locks from blkg_conf_prep/finish()")
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20231219012833.2129540-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Michal Koutný <mkoutny@suse.com>
---
 block/blk-cgroup.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index fd482439afbc..b927a4a0ad03 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -252,7 +252,8 @@ static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
 	if (blkcg == &blkcg_root)
 		return q->root_blkg;
 
-	blkg = rcu_dereference(blkcg->blkg_hint);
+	blkg = rcu_dereference_check(blkcg->blkg_hint,
+			lockdep_is_held(&q->queue_lock));
 	if (blkg && blkg->q == q)
 		return blkg;