Re: Stable backport (was "Re: PROBLEM: io_uring hang causing uninterruptible sleep state on 6.6.59")

[Jens Axboe <axboe@kernel.dk>]

On 11/4/24 6:17 AM, Andrew Marshall wrote:
> On Sun, Nov 3, 2024, at 23:25, Andrew Marshall wrote:
>> On Sun, Nov 3, 2024, at 21:38, Jens Axboe wrote:
>>> On 11/3/24 5:06 PM, Jens Axboe wrote:
>>>> On 11/3/24 5:01 PM, Keith Busch wrote:
>>>>> On Sun, Nov 03, 2024 at 04:53:27PM -0700, Jens Axboe wrote:
>>>>>> On 11/3/24 4:47 PM, Andrew Marshall wrote:
>>>>>>> I identified f4ce3b5d26ce149e77e6b8e8f2058aa80e5b034e as the likely
>>>>>>> problematic commit simply by browsing git log. As indicated above;
>>>>>>> reverting that atop 6.6.59 results in success. Since it is passing on
>>>>>>> 6.11.6, I suspect there is some missing backport to 6.6.x, or some
>>>>>>> other semantic merge conflict. Unfortunately I do not have a compact,
>>>>>>> minimal reproducer, but can provide my large one (it is testing a
>>>>>>> larger build process in a VM) if needed?there are some additional
>>>>>>> details in the above-linked downstream bug report, though. I hope that
>>>>>>> having identified the problematic commit is enough for someone with
>>>>>>> more context to go off of. Happy to provide more information if
>>>>>>> needed.
>>>>>>
>>>>>> Don't worry about not having a reproducer, having the backport commit
>>>>>> pin pointed will do just fine. I'll take a look at this.
>>>>>
>>>>> I think stable is missing:
>>>>>
>>>>>   6b231248e97fc3 ("io_uring: consolidate overflow flushing")
>>>>
>>>> I think you need to go back further than that, this one already
>>>> unconditionally holds ->uring_lock around overflow flushing...
>>>
>>> Took a look, it's this one:
>>>
>>> commit 8d09a88ef9d3cb7d21d45c39b7b7c31298d23998
>>> Author: Pavel Begunkov <asml.silence@gmail.com>
>>> Date:   Wed Apr 10 02:26:54 2024 +0100
>>>
>>>     io_uring: always lock __io_cqring_overflow_flush
>>>
>>> Greg/stable, can you pick this one for 6.6-stable? It picks
>>> cleanly.
>>>
>>> For 6.1, which is the other stable of that age that has the backport,
>>> the attached patch will do the trick.
>>>
>>> With that, I believe it should be sorted. Hopefully that can make
>>> 6.6.60 and 6.1.116.
>>>
>>> -- 
>>> Jens Axboe
>>> Attachments:
>>> * 0001-io_uring-always-lock-__io_cqring_overflow_flush.patch
>>
>> Cherry-picking 6b231248e97fc3 onto 6.6.59, I can confirm it passes my 
>> reproducer (run a few times). Your first quick patch also passed, for 
>> what it?s worth. Thanks for the quick responses!
> 
> Correction: I cherry-picked and tested
> 8d09a88ef9d3cb7d21d45c39b7b7c31298d23998 (which was the change you
> identified), not 6b231248e97fc3. Apologies for any confusion.

Thanks for clarifying, so it's as expected. Hopefully -stable can pick
this backport up soonish, so the next stable release will be sorted.
Thanks for reporting the issue!

-- 
Jens Axboe