linux-kernel - [PATCH] blk-mq: clear active_queues before clearing BLK_MQ_F_TAG_QUEUE

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Date:   Sat, 31 Jul 2021 14:21:30 +0800
From:   Yu Kuai <yukuai3@...wei.com>
To:     <axboe@...nel.dk>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yukuai3@...wei.com>, <yi.zhang@...wei.com>
Subject: [PATCH] blk-mq: clear active_queues before clearing BLK_MQ_F_TAG_QUEUE_SHARED

We run a test that delete and recover devcies frequently(two devices on
the same host), and we found that 'active_queues' is super big after a
period of time.

If device a and device b share a tag set, and a is deleted, then
blk_mq_exit_queue() will clear BLK_MQ_F_TAG_QUEUE_SHARED because there
is only one queue that are using the tag set. However, if b is still
active, the active_queues of b might never be cleared even if b is
deleted.

Thus clear active_queues before BLK_MQ_F_TAG_QUEUE_SHARED is cleared.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-mq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2c4ac51e54eb..2fe396385a4a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2994,10 +2994,12 @@ static void queue_set_hctx_shared(struct request_queue *q, bool shared)
 	int i;

 	queue_for_each_hw_ctx(q, hctx, i) {
-		if (shared)
+		if (shared) {
 			hctx->flags |= BLK_MQ_F_TAG_QUEUE_SHARED;
-		else
+		} else {
+			blk_mq_tag_idle(hctx);
 			hctx->flags &= ~BLK_MQ_F_TAG_QUEUE_SHARED;
+		}
 	}
 }

-- 
2.31.1