[PATCH 1/3] blk-throttle: fix lockdep warning of "cgroup_mutex or RCU read lock required!"

[Ming Lei <ming.lei@redhat.com>]

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>
---
 block/blk-throttle.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 38a881cf97d0..050f8ac6fcb1 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1314,6 +1314,7 @@ 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
@@ -1341,6 +1342,7 @@ 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
-- 
2.41.0