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From: Jianchao Wang <jianchao.w.wang@oracle.com>
To: axboe@kernel.dk
Cc: hch@lst.de, jthumshirn@suse.de, hare@suse.de,
	josef@toxicpanda.com, bvanassche@acm.org, sagi@grimberg.me,
	keith.busch@intel.com, jsmart2021@gmail.com,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH V2 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues
Date: Mon, 25 Mar 2019 13:38:31 +0800	[thread overview]
Message-ID: <1553492318-1810-2-git-send-email-jianchao.w.wang@oracle.com> (raw)
In-Reply-To: <1553492318-1810-1-git-send-email-jianchao.w.wang@oracle.com>

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.

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.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 a4931fc..5f28002 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 a9c1816..2102d91 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3211,10 +3211,6 @@ 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


  reply	other threads:[~2019-03-25  5:47 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-25  5:38 [PATCH V2 0/8]: blk-mq: use static_rqs to iterate busy tags Jianchao Wang
2019-03-25  5:38 ` Jianchao Wang [this message]
2019-03-25  5:38 ` [PATCH V2 2/8] blk-mq: use static_rqs instead of rqs to iterate tags Jianchao Wang
2019-03-25  7:12   ` Dongli Zhang
2019-03-25  7:14     ` jianchao.wang
2019-03-25  5:38 ` [PATCH V2 3/8] blk-mq: use blk_mq_queue_tag_inflight_iter in debugfs Jianchao Wang
2019-03-25  5:38 ` [PATCH V2 4/8] mtip32xx: use blk_mq_queue_tag_inflight_iter Jianchao Wang
2019-03-25  5:38 ` [PATCH V2 5/8] nbd: " Jianchao Wang
2019-03-25  5:38 ` [PATCH V2 6/8] skd: " Jianchao Wang
2019-03-25  5:38 ` [PATCH V2 7/8] nvme: " Jianchao Wang
2019-03-25 13:49   ` Keith Busch
2019-03-26  1:17     ` jianchao.wang
2019-03-26  2:41       ` Ming Lei
2019-03-26  3:05         ` jianchao.wang
2019-03-26 23:57           ` Keith Busch
2019-03-27  2:03             ` jianchao.wang
2019-03-27  2:15               ` Keith Busch
2019-03-27  2:27                 ` jianchao.wang
2019-03-27  2:33                   ` Keith Busch
2019-03-27  2:45                     ` jianchao.wang
2019-03-27  6:51                       ` Keith Busch
2019-03-27  7:18                         ` jianchao.wang
2019-03-25  5:38 ` [PATCH V2 8/8] blk-mq: remove blk_mq_tagset_busy_iter Jianchao Wang
2019-03-25  7:18   ` Hannes Reinecke
2019-03-25  7:37     ` jianchao.wang
2019-03-25  8:25       ` Hannes Reinecke
2019-03-25  9:12         ` jianchao.wang
2019-03-26 14:17         ` Jens Axboe

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