linux-kernel - Re: v5.9-rc3-rt3 boot time networking lockdep splat

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Message-ID: <a79815352e2f238b7f108e6e7202f6655f26159d.camel@gmx.de>
Date:   Tue, 08 Sep 2020 17:59:31 +0200
From:   Mike Galbraith <efault@....de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: v5.9-rc3-rt3 boot time networking lockdep splat

On Tue, 2020-09-08 at 17:12 +0200, Sebastian Andrzej Siewior wrote:
> On 2020-09-05 07:19:10 [+0200], Mike Galbraith wrote:
> > Lappy, which does not use bridge, boots clean... but lock leakage
> > pretty darn quickly inspires lockdep to craps its drawers.
> >
> > [  209.001111] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> > [  209.001113] turning off the locking correctness validator.
> > [  209.001114] CPU: 2 PID: 3773 Comm: Socket Thread Tainted: G S        I E     5.9.0.gc70672d-rt3-rt #8
> > [  209.001117] Hardware name: HP HP Spectre x360 Convertible/804F, BIOS F.47 11/22/2017
> > [  209.001118] Call Trace:
> > [  209.001123]  dump_stack+0x77/0x9b
> > [  209.001129]  validate_chain+0xf60/0x1230
>
> I have no idea how to debug this based on this report. Can you narrow
> it down to something?

I instrumented what I presume is still this problem once upon a time,
structures containing locks are allocated/initialized/freed again and
again with no cleanup until we increment into the wall.

> Is Lappy new, got a new something or has a new config switch? I'm just
> curious if this something or something that was always there but
> remained undetected.

Nah, this is nothing new.  Turn lockdep on in RT, it's just a matter of
time before it turns itself off.  It's usually just not _that_ quick.

	-Mike