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From:   Dexuan Cui <decui@microsoft.com>
To:     "Martin K. Petersen" <martin.petersen@oracle.com>
CC:     KY Srinivasan <kys@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        "jejb@linux.ibm.com" <jejb@linux.ibm.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "ming.lei@redhat.com" <ming.lei@redhat.com>,
        "bvanassche@acm.org" <bvanassche@acm.org>,
        "john.garry@huawei.com" <john.garry@huawei.com>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        Long Li <longli@microsoft.com>,
        Michael Kelley <mikelley@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH v3] scsi: core: Fix shost->cmd_per_lun calculation in
 scsi_add_host_with_dma()
Thread-Topic: [PATCH v3] scsi: core: Fix shost->cmd_per_lun calculation in
 scsi_add_host_with_dma()
Thread-Index: AQHXv4gYaXXuoTkdsESnUMEs4EqppKvPpJjg
Date:   Tue, 12 Oct 2021 18:05:47 +0000
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> From: Martin K. Petersen <martin.petersen@oracle.com>
> Sent: Tuesday, October 12, 2021 9:42 AM
>=20
> Dexuan,
>=20
> > After commit ea2f0f77538c, a 416-CPU VM running on Hyper-V hangs during
> > boot because the hv_storvsc driver sets scsi_driver.can_queue to an "in=
t"
> > value that exceeds SHRT_MAX, and hence scsi_add_host_with_dma() sets
> > shost->cmd_per_lun to a negative "short" value.
> >
> > Use min_t(int, ...) to fix the issue.
>=20
> I queued this up as a short term workaround. However, I am hoping that
> the rework of the scaling code in storvsc lands soon.

Thanks, Martin! I know Michael Kelley will improve the netvsc.

Regarding this patch, I'm not sure if it's a "workaround": if it's incorrec=
t to
set a bigger-than-SHRT_MAX scsi_driver.can_queue value, probably we should
change scsi_driver.can_queue from "int" to "u16"? BTW, I guess the "cmd_per=
_lun"
should also be "u16" rather than "short"?

This was discussed in May, and it looks like the conclusion was not clear t=
o me:
https://lwn.net/ml/linux-kernel/457d23a9-deb0-4ee1-fe7f-5a63605d9686@huawei=
.com/

Thanks,
-- Dexuan