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From:   zhengbin <zhengbin13@huawei.com>
To:     <axboe@kernel.dk>, <ming.lei@redhat.com>, <hch@lst.de>,
        <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>
CC:     <houtao1@huawei.com>, <yanaijie@huawei.com>, <yuyufen@huawei.com>
Subject: [PATCH] blk-mq: fix a hung issue when set device state to blocked and restore running
Date:   Wed, 20 Mar 2019 16:02:01 +0800
Message-ID: <1553068921-6605-1-git-send-email-zhengbin13@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
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When I use dd test a SCSI device which use blk-mq in the following steps:
1.echo "blocked" >/sys/block/sda/device/state
2.dd if=/dev/sda of=/mnt/t.log bs=1M count=10
3.echo "running" >/sys/block/sda/device/state
dd should finish this work after step 3, unfortunately, still hung.

After step2, the key code process is like this:
blk_mq_dispatch_rq_list-->scsi_queue_rq-->prep_to_mq
                       -->if ret is BLK_STS_RESOURCE, delay run hw queue

prep_to_mq will return BLK_STS_RESOURCE, and scsi_queue_rq will transter
it to BLK_STS_DEV_RESOURCE. In this situtation, we should delay run hw
queue. This patch fixes that.

Fixes: 86ff7c2a80cd ("blk-mq: introduce BLK_STS_DEV_RESOURCE")
Signed-off-by: zhengbin <zhengbin13@huawei.com>
---
 block/blk-mq.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a9c1816..556d606 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1309,15 +1309,17 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 		 *   returning BLK_STS_RESOURCE. Two exceptions are scsi-mq
 		 *   and dm-rq.
 		 *
-		 * If driver returns BLK_STS_RESOURCE and SCHED_RESTART
-		 * bit is set, run queue after a delay to avoid IO stalls
-		 * that could otherwise occur if the queue is idle.
+		 * If driver returns BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE
+		 * and SCHED_RESTART bit is set, run queue after a delay to
+		 * avoid IO stalls that could otherwise occur if the queue
+		 * is idle.
 		 */
 		needs_restart = blk_mq_sched_needs_restart(hctx);
 		if (!needs_restart ||
 		    (no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))
 			blk_mq_run_hw_queue(hctx, true);
-		else if (needs_restart && (ret == BLK_STS_RESOURCE))
+		else if (needs_restart && ((ret == BLK_STS_RESOURCE) ||
+					   (ret == BLK_STS_DEV_RESOURCE)))
 			blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);

 		blk_mq_update_dispatch_busy(hctx, true);
--
2.7.4