Re: [PATCH] iommu: Avoid softlockup and rcu stall in fq_flush_timeout().

[John Garry]

On 22/05/2023 16:18, Jerry Snitselaar wrote:
> > My guess is that the allocations are too big and not covered by the
> > allocation sizes supported by the flush-queue code. But maybe this is
> > something that can be fixed. Or the flush-queue code could even be
> > changed to auto-adapt to allocation patterns of the device driver?
> >
> > Regards,
> >
> > 	Joerg
> In the case I know of it involved some proprietary test suites
> (Hazard I/O, and Medusa?), and the lpfc driver. I was able to force
> the condition using fio with a number of jobs running. I'll play
> around and see if I can figure out a point where it starts to become
> an issue.
>
> I mentioned what the nvme driver did to the Broadcom folks for the max
> dma size, but I haven't had a chance to go looking at it myself yet to
> see if there is somewhere in the lpfc code to fix up.

JFYI, SCSI core already supports setting this in shost->opt_sectors, see 
example in sas_host_setup().

This issue may continue to pop up so we may need a better way to turn it 
on/off for all drivers or classes of drivers.

John