On Mon, Oct 21, 2019 at 03:42:56PM -0700, Bart Van Assche wrote:
> Since the blk_mq_{,un}freeze_queue() calls in __blk_mq_update_nr_hw_queues()
> already serialize __blk_mq_update_nr_hw_queues() against
> blk_mq_queue_tag_busy_iter(), the synchronize_rcu() call in
> __blk_mq_update_nr_hw_queues() is not necessary. Hence remove it.
>
> Note: the synchronize_rcu() call in __blk_mq_update_nr_hw_queues() was
> introduced by commit f5bbbbe4d635 ("blk-mq: sync the update nr_hw_queues with
> blk_mq_queue_tag_busy_iter"). Commit 530ca2c9bd69 ("blk-mq: Allow blocking
> queue tag iter callbacks") removed the rcu_read_{,un}lock() calls that
> correspond to the synchronize_rcu() call in __blk_mq_update_nr_hw_queues().
>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/blk-mq.c | 4 ----
> 1 file changed, 4 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8538dc415499..7528678ef41f 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3242,10 +3242,6 @@ 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
> --
> 2.23.0.866.gb869b98d4c-goog
>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
--
Ming
