Subject: [PATCH 2/2] scsi: core: fix dh and multipathing for SCSI hosts without request batching

From: Steffen Maier <[email-masked]>
Date: Wed, 7 Aug 2019 16:49:48 +0200

This was missing from scsi_device_from_queue() due to the introduction
of another new scsi_mq_ops_no_commit of linux-next commit
8930a6c20791 ("scsi: core: add support for request batching")
from Martin's scsi/5.4/scsi-queue or James' scsi/misc.

Only devicehandler code seems to call scsi_device_from_queue():
*** drivers/scsi/scsi_dh.c:
scsi_dh_activate[255]          sdev = scsi_device_from_queue(q);
scsi_dh_set_params[302]        sdev = scsi_device_from_queue(q);
scsi_dh_attach[325]            sdev = scsi_device_from_queue(q);
scsi_dh_attached_handler_name[363] sdev = scsi_device_from_queue(q);

Fixes multipath tools follow-on errors:

$ multipath -v6
...
libdevmapper: ioctl/libdm-iface.c(1887): device-mapper: reload ioctl on mpatha  failed: No such device
...
mpatha: failed to load map, error 19
...

showing also as kernel messages:

device-mapper: table: 252:0: multipath: error attaching hardware handler
device-mapper: ioctl: error adding target to table

Signed-off-by: Steffen Maier <[email-masked]>
Fixes: 8930a6c20791 ("scsi: core: add support for request batching")
Cc: Paolo Bonzini <[email-masked]>
---
 drivers/scsi/scsi_lib.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 90c257622bb0..73e7d29fbd66 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1922,7 +1922,8 @@ struct scsi_device *scsi_device_from_queue(struct request_queue *q)
 {
 	struct scsi_device *sdev = NULL;
 
-	if (q->mq_ops == &scsi_mq_ops)
+	if (q->mq_ops == &scsi_mq_ops_no_commit ||
+	    q->mq_ops == &scsi_mq_ops)
 		sdev = q->queuedata;
 	if (!sdev || !get_device(&sdev->sdev_gendev))
 		sdev = NULL;
-- 
2.17.1