linux-kernel - RE: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK

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Message-ID: <F6531D8286A0B34FBC858F176F707962027B9228C9@LGEVEXMBHQSVC1.LGE.NET>
Date:   Thu, 19 Oct 2017 18:02:21 +0900
From:   박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@....com) 
        <byungchul.park@....com>
To:     Ingo Molnar <mingo@...nel.org>,
        Byungchul Park <byungchul.park@....com>
CC:     "peterz@...radead.org" <peterz@...radead.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kernel-team@....com" <kernel-team@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: RE: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK_TRACE and
 make it not unwind as default

> -----Original Message-----
> From: Ingo Molnar [mailto:mingo.kernel.org@...il.com] On Behalf Of Ingo
> 
> > At the time, cross-release was falsely accused. AFAIK, cross-release has
> > not crashed system yet.
> 
> I'm talking about the crash fixed here:
> 
>   8b405d5c5d09: locking/lockdep: Fix stacktrace mess
> 
> Which was introduced by your patch:
> 
>   ce07a9415f26: locking/lockdep: Make check_prev_add() able to handle
> external stack_trace
> 
> ... which was a preparatory patch for cross-release. So 'technically' it's not a
> cross-release crash, but was very much related. It even says so in the changelog:
> 
>   Actually crossrelease needs to do other than saving a stack_trace.
>   So pass a stack_trace and callback to handle it, to check_prev_add().
> 
> ... so let's not pretend it wasn't related, ok?

I don't want to pretend I'm perfect. Of course, I can make mistakes.
I'm just saying that *I have not seen* any crash by cross-release.

In that case you pointed out, likewise, the crash was caused by ae813308f:
lockdep: Avoid creating redundant links, which is not related to the feature
actually. It was also falsely accused at the time again...

Of course, it's my fault not to have made the design more robust so that
others can modify lockdep code caring less after cross-release commit.
That's what I'm sorry for.

I already mentioned the above in the thread talking about the issue you
are pointing now. Of course, I basically appreciate all comments and
suggestions you have given, but you seem to have mis-understood some
issues wrt cross-release feature.

Thanks,
Byungchul