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Subject: Re: [BUG] kernel BUG at mm/slub.c - possible BFQ issue?
From:   Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <1889051823.161943.1633100469857@office.mailbox.org>
Date:   Tue, 5 Oct 2021 17:06:40 +0200
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
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References: <1624640454.149631.1632987871186@office.mailbox.org>
 <1889051823.161943.1633100469857@office.mailbox.org>
To:     torvic9@mailbox.org
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> Il giorno 1 ott 2021, alle ore 17:01, torvic9@mailbox.org ha scritto:
> 
>> torvic9@mailbox.org hat am 30.09.2021 09:44 geschrieben:
>> 
>> 
>> Hello,
>> 
>> I encounter a hard freeze on both 5.14 and 5.15 when using BFQ.
>> Unfortunately, I do not have a full error log, because the computer
>> totally freezes and slightly corrupts the display, so it's
>> impossible to read the entire message.
>> 
>> However, what I could get is the following:
>> 
>>  kernel BUG at mm/slub.c:379
>>  invalid opcode: 0000 [#1]
>>  RIP: 0010:__slab_free
>>  [...]
>>  Call Trace:
>>  bfq_set_next_ioprio_data
>>  [...]
>>  bfq_put_queue
>>  bfq_insert_requests
>>  [...]
>> 
>> This issue appears more or less randomly and it sometimes takes a
>> little while to reproduce it (running fio helps).
>> The call trace always contains references to BFQ, but they are not
>> always the exact same. Once, I could see on the corrupted display
>> the message "general protection fault".
>> I could reproduce this issue on two computers.
>> 
>> Not quite sure but I *think* the issue first appeared somewhere around
>> 5.14.5 or 5.14.6, during which time BFQ only got the following commit:
>> 
>>  (88013a0c5d99) block, bfq: honor already-setup queue merges
> 
> I have now reverted the above commit and launched some heavy I/O like
> e.g. git kernel, fio, xz compression, and so far, no freezes anymore!
> Too early to say that this commit really is the cause though.
> Would be great if someone could have a look at it.
> 

Hi,
sorry for the delay and that you very much for reporting this crash.
I have prepared a dev version of BFQ, to try to solve this problem.
It's based on a 5.12.0, and should hopefully provide more information
upon failure.  Could you please give it a try?  You can find it here:
https://github.com/Algodev-github/bfq-mq/tree/dev-bfq-on-5.12

Thanks for your help,
Paolo


>> 
>> 5.13 doesn't seem to be affected AFAICS.
>> 
>> Does anyone have an idea what is going on?
>> I will now revert the above commit and see if that helps...
>> 
>> Thanks,
>> Tor