-----Original Message-----
From: Dexuan Cui <decui@microsoft.com>
Sent: Thursday, October 7, 2021 1:50 PM
To: KY Srinivasan <kys@microsoft.com>; Stephen Hemminger
[off-list ref]; wei.liu@kernel.org; jejb@linux.ibm.com;
martin.petersen@oracle.com; Haiyang Zhang [off-list ref];
ming.lei@redhat.com; bvanassche@acm.org; john.garry@huawei.com; linux-
scsi@vger.kernel.org; linux-hyperv@vger.kernel.org; Long Li
[off-list ref]; Michael Kelley [off-list ref]
Cc: linux-kernel@vger.kernel.org; Dexuan Cui <decui@microsoft.com>;
stable@vger.kernel.org
Subject: [PATCH v2] scsi: core: Fix shost->cmd_per_lun calculation in
scsi_add_host_with_dma()

After commit ea2f0f77538c, a 416-CPU VM running on Hyper-V hangs during
boot because scsi_add_host_with_dma() sets shost->cmd_per_lun to a
negative number (the below numbers may differ in different kernel
versions):
in drivers/scsi/storvsc_drv.c, 	storvsc_drv_init() sets
'max_outstanding_req_per_channel' to 352, and storvsc_probe() sets
'max_sub_channels' to (416 - 1) / 4 = 103 and sets scsi_driver.can_queue
to
352 * (103 + 1) * (100 - 10) / 100 = 32947, which exceeds SHRT_MAX.

Use min_t(int, ...) to fix the issue.

Fixes: ea2f0f77538c ("scsi: core: Cap scsi_host cmd_per_lun at
can_queue")
Cc: stable@vger.kernel.org
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---

v1 tried to fix the issue by changing the storvsc driver:
https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.ne
t%2Fml%2Flinux-
kernel%2FBYAPR21MB1270BBC14D5F1AE69FC31A16BFB09%40BYAPR21MB1270.namprd21
.prod.outlook.com%2F&amp;data=04%7C01%7Chaiyangz%40microsoft.com%7C366e6
d0bf755492c631c08d989baf4b9%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7
C637692258384408217%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoi
V2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=RbNgx1aBBBzfHC3p
EdKyBZWaaQIQXS3U%2FItEQUe4NfQ%3D&amp;reserved=0

v2 directly fixes the scsi core change instead as Michael Kelley and
John Garry suggested (refer to the above link).

 drivers/scsi/hosts.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 3f6f14f0cafb..24b72ee4246f 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c

@@ -220,7 +220,8 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost,

struct device *dev,
 		goto fail;
 	}

-	shost->cmd_per_lun = min_t(short, shost->cmd_per_lun,
+	/* Use min_t(int, ...) in case shost->can_queue exceeds SHRT_MAX */
+	shost->cmd_per_lun = min_t(int, shost->cmd_per_lun,
 				   shost->can_queue);