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Message-ID: <57017dea-c453-82bc-18b1-79663e77552d@oracle.com>
Date:   Mon, 22 May 2023 16:35:34 +0100
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Subject: Re: [PATCH] iommu: Avoid softlockup and rcu stall in
 fq_flush_timeout().
To:     Jerry Snitselaar <jsnitsel@redhat.com>,
        Joerg Roedel <joro@8bytes.org>
Cc:     Vasant Hegde <vasant.hegde@amd.com>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        Robin Murphy <robin.murphy@arm.com>, will@kernel.org,
        iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
        Li Bin <huawei.libin@huawei.com>,
        Xie XiuQi <xiexiuqi@huawei.com>,
        Yang Yingliang <yangyingliang@huawei.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
References: <20230216071148.2060-1-zhangpeng.00@bytedance.com>
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From:   John Garry <john.g.garry@oracle.com>
Organization: Oracle Corporation
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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