[PATCH AUTOSEL 6.6 05/40] blk-throttle: fix lockdep warning of "cgroup_mutex or RCU read lock required!"

Sasha Levin
2023-11-28T21:06:48Z

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 27b13e209ddca5979847a1b57890e0372c1edcee ]

Inside blkg_for_each_descendant_pre(), both
css_for_each_descendant_pre() and blkg_lookup() requires RCU read lock,
and either cgroup_assert_mutex_or_rcu_locked() or rcu_read_lock_held()
is called.

Fix the warning by adding rcu read lock.

Reported-by: Changhui Zhong <czhong@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20231117023527.3188627-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-throttle.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 13e4377a8b286..16f5766620a41 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1320,6 +1320,7 @@ static void tg_conf_updated(struct throtl_grp *tg, bool global)
tg_bps_limit(tg, READ), tg_bps_limit(tg, WRITE),
tg_iops_limit(tg, READ), tg_iops_limit(tg, WRITE));

+ rcu_read_lock();
/*
* Update has_rules[] flags for the updated tg's subtree. A tg is
* considered to have rules if either the tg itself or any of its
@@ -1347,6 +1348,7 @@ static void tg_conf_updated(struct throtl_grp *tg, bool global)
this_tg->latency_target = max(this_tg->latency_target,
parent_tg->latency_target);
}
+ rcu_read_unlock();

/*
* We're already holding queue_lock and know @tg is valid. Let's
--
2.42.0