linux-kernel - Re: Bug#1093243: Upgrade to 6.1.123 kernel causes mariadb hangs

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Message-ID: <117696e5-6649-4236-a06d-a860b29b3cba@gmail.com>
Date: Mon, 27 Jan 2025 16:49:26 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Xan Charbonnet <xan@...rbonnet.com>, Jens Axboe <axboe@...nel.dk>,
 Salvatore Bonaccorso <carnil@...ian.org>
Cc: 1093243@...s.debian.org, Bernhard Schmidt <berni@...ian.org>,
 io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev
Subject: Re: Bug#1093243: Upgrade to 6.1.123 kernel causes mariadb hangs

On 1/26/25 22:48, Xan Charbonnet wrote:
> Since applying the final patch on Friday, I have seen no problems with either the backup snapshot or catching up with replication.  It sure seems like things are all fixed.  I haven't yet tried it on our production Galera cluster, but I expect to on Monday.

Great to hear that, thanks for the update. And I sent the fix,
hopefully it'll be merged for the nearest stable release.


> Here are Debian packages containing the modified kernel.  Use at your own risk of course.  Any feedback about how this works or doesn't work would be very helpful.
> 
> https://charbonnet.com/linux-image-6.1.0-29-with-proposed-1093243-fix_amd64.deb
> https://charbonnet.com/linux-image-6.1.0-30-with-proposed-1093243-fix_amd64.deb
> 
> 
> 
> 
> On 1/24/25 14:51, Jens Axboe wrote:
>> On 1/24/25 1:33 PM, Salvatore Bonaccorso wrote:
>>> Hi Pavel,
>>>
>>> On Fri, Jan 24, 2025 at 06:40:51PM +0000, Pavel Begunkov wrote:
>>>> On 1/24/25 16:30, Xan Charbonnet wrote:
>>>>> On 1/24/25 04:33, Pavel Begunkov wrote:
>>>>>> Thanks for narrowing it down. Xan, can you try this change please?
>>>>>> Waiters can miss wake ups without it, seems to match the description.
>>>>>>
>>>>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>>>>>> index 9b58ba4616d40..e5a8ee944ef59 100644
>>>>>> --- a/io_uring/io_uring.c
>>>>>> +++ b/io_uring/io_uring.c
>>>>>> @@ -592,8 +592,10 @@ static inline void __io_cq_unlock_post_flush(struct io_ring_ctx *ctx)
>>>>>>         io_commit_cqring(ctx);
>>>>>>         spin_unlock(&ctx->completion_lock);
>>>>>>         io_commit_cqring_flush(ctx);
>>>>>> -    if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
>>>>>> +    if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN)) {
>>>>>> +        smp_mb();
>>>>>>             __io_cqring_wake(ctx);
>>>>>> +    }
>>>>>>     }
>>>>>>     void io_cq_unlock_post(struct io_ring_ctx *ctx)
>>>>>>
>>>>>
>>>>>
>>>>> Thanks Pavel!  Early results look very good for this change.  I'm now running 6.1.120 with your added smp_mb() call.  The backup process which had been quickly triggering the issue has been running longer than it ever did when it would ultimately fail.  So that's great!
>>>>>
>>>>> One sour note: overnight, replication hung on this machine, which is another failure that started happening with the jump from 6.1.119 to 6.1.123.  The machine was running 6.1.124 with the __io_cq_unlock_post_flush function removed completely.  That's the kernel we had celebrated yesterday for running the backup process successfully.
>>>>>
>>>>> So, we might have two separate issues to deal with, unfortunately.
>>>>
>>>> Possible, but it could also be a side effect of reverting the patch.
>>>> As usual, in most cases patches are ported either because they're
>>>> fixing sth or other fixes depend on it, and it's not yet apparent
>>>> to me what happened with this one.
>>>
>>> I researched bit the lists, and there was the inclusion request on the
>>> stable list itself. Looking into the io-uring list I found
>>> https://lore.kernel.org/io-uring/CADZouDRFJ9jtXHqkX-PTKeT=GxSwdMC42zEsAKR34psuG9tUMQ@mail.gmail.com/
>>> which I think was the trigger to later on include in fact the commit
>>> in 6.1.120.
>>
>> Yep indeed, was just looking for the backstory and that is why it got
>> backported. Just missed the fact that it should've been an
>> io_cqring_wake() rather than __io_cqring_wake()...
>>
> 

-- 
Pavel Begunkov