linux-kernel - Re: [PATCH 2/2] lockdep: Up MAX_LOCKDEP

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Message-ID: <20171130074718.hzed67wrwjtv4byu@hirez.programming.kicks-ass.net>
Date:   Thu, 30 Nov 2017 08:47:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Tejun Heo <tj@...nel.org>, Kees Cook <keescook@...omium.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Marta Lofstedt <marta.lofstedt@...el.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 2/2] lockdep: Up MAX_LOCKDEP_CHAINS

On Wed, Nov 29, 2017 at 04:41:45PM +0100, Daniel Vetter wrote:
> cross-release ftl
> 
> From Chris:
> 
> "Fwiw, this isn't cross-release but us reloading the module many times,
> creating a whole host of new lockclasses. Even more fun is when the
> module gets a slightly different address and the new lock address hashes
> into an old lock...

Yeah, this is a known issue, just reboot.

> "I did think about a module-hook to revoke the stale lockclasses, but
> that still leaves all the hashed chains.

Its an absolute royal pain to remove all the resources consumed by a
module, and if you manage you then have to deal with fragmented storage
-- that is, we need to go keep track of which entries are used.

Its a giant heap of complexity that's just not worth it.


Given all that, I don't see why we should up this. Just don't reload
modules (or better, don't use modules at all).