linux-kernel - [PATCH V4] scsi: core: use blk_mq_requeue_request in __scsi_queue

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Date:   Sat,  3 Mar 2018 09:54:09 +0800
From:   Jianchao Wang <jianchao.w.wang@...cle.com>
To:     jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com
Cc:     Bart.VanAssche@....com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: [PATCH V4] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert

In scsi core, __scsi_queue_insert should just put request back on
the queue and retry using the same command as before. However, for
blk-mq, scsi_mq_requeue_cmd is employed here which will unprepare
the request. To align with the semantics of __scsi_queue_insert,
use blk_mq_requeue_request with kick_requeue_list == true and put
the reference of scsi_device.

Cc: Christoph Hellwig <hch@....de>
Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
Reviewed-by: Bart Van Assche <bart.vanassche@....com>
---
Changelog:
V3 -> V4:
 - modify the comment and make it more clearly

V2 -> V3:
 - add comment to explain why we need a put_device in
   __scsi_queue_insert
 - add reviewed-by

V1 -> V2:
 - add put_device on scsi_device->sdev_gendev
 drivers/scsi/scsi_lib.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a86df9c..6ce33f6 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -191,7 +191,19 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, bool unbusy)
 	 */
 	cmd->result = 0;
 	if (q->mq_ops) {
-		scsi_mq_requeue_cmd(cmd);
+		/*
+		 * Before a SCSI command is dispatched,
+		 * get_device(&sdev->sdev_gendev) is called and the host,
+		 * target and device busy counters are increased. Since
+		 * requeuing a request causes these actions to be repeated and
+		 * since scsi_device_unbusy() has already been called,
+		 * put_device(&device->sdev_gendev) must still be called. Call
+		 * put_device() after blk_mq_requeue_request() to avoid that
+		 * removal of the SCSI device can start before requeueing has
+		 * happened.
+		 */
+		blk_mq_requeue_request(cmd->request, true);
+		put_device(&device->sdev_gendev);
 		return;
 	}
 	spin_lock_irqsave(q->queue_lock, flags);
-- 
2.7.4