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

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Date:   Thu, 29 Nov 2018 23:48:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
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 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