On Fri, Mar 15, 2019 at 5:07 PM Jianchao Wang <jianchao.w.wang@xxxxxxxxxx> wrote: > > 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 <jianchao.w.wang@xxxxxxxxxx> > --- > 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 > Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> Thanks, Ming Lei
