linux-kernel - Re: [BUG] btrfs: MAX_LOCKDEP_CHAIN

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Message-ID: <721575ee-4a48-dab1-eabd-32428c20cc72@alu.unizg.hr>
Date:   Tue, 27 Jun 2023 20:16:51 +0200
From:   Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
To:     dsterba@...e.cz
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Subject: Re: [BUG] btrfs: MAX_LOCKDEP_CHAIN_HLOCKS too low!

On 6/27/23 18:27, Mirsad Goran Todorovac wrote:
> Hi, Qu, David,
> 
> On 6/27/23 16:27, David Sterba wrote:
>> On Tue, Jun 27, 2023 at 08:19:37AM +0800, Qu Wenruo wrote:
>>>
>>> On 2023/6/27 07:40, Mirsad Goran Todorovac wrote:
>>>> Hi,
>>>>
>>>> There is a bug apparently in btrfs file system.
>>>>
>>>> The platform is an assembled box with Ryzen 9 processor and ASRock X670E PG
>>>> Lightning motherboard.
>>>>
>>>> I do not have a reproducer, just kernel log:
>>>>
>>>> Jun 26 20:41:58 defiant kernel: [ 2273.786736] BUG:
>>>> MAX_LOCKDEP_CHAIN_HLOCKS too low!
>>>
>>> This is really what it said.
>>>
>>> The setting is too low for certain workload.
>>>
>>> In fact Fedora is already increasing this value.
>>> If you want lockdep, I guess that's the only way to go.
>>
>> https://btrfs.readthedocs.io/en/latest/dev/Development-notes.html#bug-max-lockdep-chain-hlocks-too-low
>>
>> As the reports will probably keep coming until lockdep changes I'll move
>> the answer to a more user-visible page.
> 
> Thank you for your prompt response. It wasn't obvious from the kernel
> message though which .config setting needs adjustment.
> 
> I am yet unable to tell whether the lockdep setting being too low and
> turning off the locking correctness validator caused the kernel crash, but
> I will know more after restarting the kselftest with the new lockdep
> setting ...

P.S.

I heard it is uncool to answer one's own email, but I have been unable to
reproduce the crash of yesterday without or with pcscd smartcard daemon
in debug mode.

This of course doesn't mean that the LOCKDEP setting was a direct cause
of crash, I believe that findings are inconclusive. (IMHO, correct locking
should work even with locking correctness validator turned off.)

FYI, here are the crash logs, in case it could help improve btrfs:

[1] https://domac.alu.unizg.hr/~mtodorov/linux/crashes/2023-06-27/

Best regards,
Mirsad Todorovac