linux-kernel - Re: [PATCH 0/2] locking/lockdep: Track number of zapped classes & report abuse

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Message-ID: <0c6c14e0-2c85-d4b7-bfa6-345cfae0d8b2@redhat.com>
Date:   Fri, 30 Nov 2018 09:38:31 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH 0/2] locking/lockdep: Track number of zapped classes &
 report abuse

On 11/29/2018 05:48 PM, Peter Zijlstra wrote:
> On Thu, Nov 29, 2018 at 05:41:35PM -0500, Waiman Long wrote:
>> When a kernel module is repeatedly load and unload, it will eventually
>> exhaust the lockdep entries resulting in a bug message. This is a use
>> case that the current lockdep code cannot support.
>>
>> This patchset tracks the number of zapped classes and print a warning if
>> too many lockdep entries are wasted because of too many module unloading.
>> For example,
>>
>> [ 2490.651531] BUG: MAX_LOCKDEP_KEYS too low!
>> [ 2490.669925] turning off the locking correctness validator.
>> [ 2490.669925] Please attach the output of /proc/lock_stat to the bug report
>> [ 2490.669926] ========================================================
>> [ 2490.669927] WARNING: 6499 out of 8191 locks have been destroyed
>> [ 2490.669927] through kernel module unload operations.
>> [ 2490.669928] The corresponding lockdep entries are not reusable.
>> [ 2490.669928] The system might have run out of lockdep entries because
>> [ 2490.669929] of repeated kernel module load and unload operations.
>> [ 2490.669929] Lockdep cannot support this particular use case.
>> [ 2490.669930] --------------------------------------------------------
> Have a look here:
>
>   https://lkml.kernel.org/r/20181128234325.110011-1-bvanassche@acm.org

Thanks for the pointer, I will take a look at that.

Cheers,
Longman