blk-throttle: fix lockdep warning of "cgroup_mutex or RCU read lock required!"

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>

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 13e4377a8b2865f527019830074e0febbd7a766e..16f5766620a41043645756c51d441f4488af9edf 100644 (file)
--- 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