In commit 530ca2c (blk-mq: Allow blocking queue tag iter callbacks),
we try to get a non-zero q_usage_counter to avoid access hctxs that
being modified. So the synchronize_rcu is useless and should be
removed.

Signed-off-by: Jianchao Wang <redacted>
---
 block/blk-mq-tag.c | 4 +---
 block/blk-mq.c     | 4 ----
 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 2089c6c..b792537 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c

@@ -384,9 +384,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
        /*
         * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx
         * while the queue is frozen. So we can use q_usage_counter to avoid
-        * racing with it. __blk_mq_update_nr_hw_queues() uses
-        * synchronize_rcu() to ensure this function left the critical section
-        * below.
+        * racing with it.
         */
        if (!percpu_ref_tryget(&q->q_usage_counter))
                return;

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9437a5e..07584a9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -3208,10 +3208,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
        list_for_each_entry(q, &set->tag_list, tag_set_list)
                blk_mq_freeze_queue(q);
        /*
-        * Sync with blk_mq_queue_tag_busy_iter.
-        */
-       synchronize_rcu();
-       /*
         * Switch IO scheduler to 'none', cleaning up the data associated
         * with the previous scheduler. We will switch back once we are done
         * updating the new sw to hw queue mappings.
--

2.7.4