Re: blktests failures with v5.19-rc1

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

Shinichiro,

On 6/13/22 19:23, Keith Busch wrote:
> On Tue, Jun 14, 2022 at 01:09:07AM +0000, Shinichiro Kawasaki wrote:
>> (CC+: linux-pci)
>> On Jun 11, 2022 / 16:34, Yi Zhang wrote:
>>> On Fri, Jun 10, 2022 at 10:49 PM Keith Busch <kbusch@kernel.org> wrote:
>>>>
>>>> And I am not even sure this is real. I don't know yet why this is showing up
>>>> only now, but this should fix it:
>>>
>>> Hi Keith
>>>
>>> Confirmed the WARNING issue was fixed with the change, here is the log:
>>
>> Thanks. I also confirmed that Keith's change to add __ATTR_IGNORE_LOCKDEP to
>> dev_attr_dev_rescan avoids the fix, on v5.19-rc2.
>>
>> I took a closer look into this issue and found The deadlock WARN can be
>> recreated with following two commands:
>>
>> # echo 1 > /sys/bus/pci/devices/0000\:00\:09.0/rescan
>> # echo 1 > /sys/bus/pci/devices/0000\:00\:09.0/remove
>>
>> And it can be recreated with PCI devices other than NVME controller, such as
>> SCSI controller or VGA controller. Then this is not a storage sub-system issue.
>>
>> I checked function call stacks of the two commands above. As shown below, it
>> looks like ABBA deadlock possibility is detected and warned.
> 
> Yeah, I was mistaken on this report, so my proposal to suppress the warning is
> definitely not right. If I run both 'echo' commands in parallel, I see it
> deadlock frequently. I'm not familiar enough with this code to any good ideas
> on how to fix, but I agree this is a generic pci issue.

I think it is worth adding a testcase to blktests to make sure these
future releases will test this.

-ck