linux-kernel - [PATCH AUTOSEL 6.6 05/40] blk-throttle: fix lockdep warning of "cgroup

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Date:   Tue, 28 Nov 2023 16:05:11 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Changhui Zhong <czhong@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        tj@...nel.org, josef@...icpanda.com, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 6.6 05/40] blk-throttle: fix lockdep warning of "cgroup_mutex or RCU read lock required!"

From: Ming Lei <ming.lei@...hat.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@...hat.com>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Link: https://lore.kernel.org/r/20231117023527.3188627-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.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