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Date: Fri, 15 Mar 2019 16:57:37 +0800 From: Jianchao Wang <jianchao.w.wang@...cle.com> To: axboe@...nel.dk Cc: hch@....de, jthumshirn@...e.de, hare@...e.de, josef@...icpanda.com, bvanassche@....org, sagi@...mberg.me, keith.busch@...el.com, jsmart2021@...il.com, linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: [PATCH 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues 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@...cle.com> --- 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
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