RE: [PATCH v3] scsi: core: Fix shost->cmd_per_lun calculation in scsi_add_host_with_dma()

Dexuan Cui
2021-10-12T18:05:59Z

> From: Martin K. Petersen <martin.petersen@oracle.com>
> Sent: Tuesday, October 12, 2021 9:42 AM
>
> Dexuan,
>
> > 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 "int"
> > 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.
>
> 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 incorrect 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 to me:
https://lwn.net/ml/linux-kernel/457d23a9-deb0-4ee1-fe7f-5a63605d9686@huawei.com/

Thanks,
-- Dexuan