linux-kernel - Re: "cat /proc/lockdep" after "rmmod <some module>" when !debug

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Date:   Tue, 26 Mar 2019 10:44:15 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     shenghui <shhuiw@...mail.com>, peterz@...radead.org,
        mingo@...hat.com, will.deacon@....com, linux-kernel@...r.kernel.org
Subject: Re: "cat /proc/lockdep" after "rmmod <some module>" when
 !debug_locks will crash the system

On Tue, 2019-03-26 at 08:35 +0800, shenghui wrote:
> My test steps:
> --------------
> 1) bootup the system, and check the calltrace in dmesg. Just warning and ignore it.
> 2) cat /proc/lockdep   # everything is well
> 3) rmmod some module which provides lock_class in lockdep
>    In my system, module bcache is used:  ('grep bcache /proc/lockdep' prints something)
>         * stop bcache set
>         * rmmod bcache
>    I have tried other module, e.g: rmmod iwldvm
> 4) cat /proc/lockdep   # system crash

Hi shenghui,

Thank you for having shared your test steps. I ran a slightly different test
myself:

while true; do cat /proc/lockdep >/dev/null; done &
(cd blktests && while ./check -q; do :; done)

This test reads /proc/lockdep in a loop while running a test that stresses
lockdep and also that loads and unloads kernel modules. Since this test
passed on my setup I suggest that you have a close look at your setup. The
vboxdrv kernel driver or an out-of-tree patch may be what is making your
system unstable.

Bart.