From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752062AbdJJFsG (ORCPT <rfc822;w@1wt.eu>);
        Tue, 10 Oct 2017 01:48:06 -0400
Received: from LGEAMRELO12.lge.com ([156.147.23.52]:36053 "EHLO
        lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751809AbdJJFsF (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 10 Oct 2017 01:48:05 -0400
X-Original-SENDERIP: 156.147.1.126
X-Original-MAILFROM: byungchul.park@lge.com
X-Original-SENDERIP: 10.177.222.33
X-Original-MAILFROM: byungchul.park@lge.com
Date: Tue, 10 Oct 2017 14:48:01 +0900
From: Byungchul Park <byungchul.park@lge.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>, Ingo Molnar <mingo@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        LKP <lkp@01.org>, Josh Poimboeuf <jpoimboe@redhat.com>,
        kernel-team@lge.com
Subject: Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer
 dereference at 000001f2
Message-ID: <20171010054801.GD3323@X58A-UD3R>
References: <20171003140634.r2jzujgl62ox4uzh@wfg-t540p.sh.intel.com>
 <CA+55aFxa_1pCMt-GQmBZUzRbc8_UY9sacmEaCqkDM1_=sq8y_A@mail.gmail.com>
 <CA+55aFz2dfH69tUX4GBWmU14=uMseLd_21dAvjohOtJYnfoe7A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+55aFz2dfH69tUX4GBWmU14=uMseLd_21dAvjohOtJYnfoe7A@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Oct 03, 2017 at 09:57:02AM -0700, Linus Torvalds wrote:
> On Tue, Oct 3, 2017 at 9:54 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Can we consider just reverting the crossrelease thing?
> >
> > The apparent stack corruption really worries me [...]
> 
> Side note: I also think the thing is just broken.
> 
> Any actual cross-releaser should be way more annotated than just "set
> cross to 1" in the lockdep map.
> 
> The place where the release is done should simply be special.
> 
> Because we should *not* encourage the whole "acquire by one context,
> release by another" as being something normal and "just set the flag
> to let lockdep know".

Could you explain it more? Please let me apply what you point out. Now,
I don't understand your intention.

> So that commit is apparently buggy, but I think it might be more
> fundamentally the wrong model too.

It would be appriciated if you let me know what is buggy wrt
crossrelease and the model, then I will do my best to fix it.

But I believe the model crossrelease uses is what lockdep should have
adopted before.

Anyway, I might be wrong. It would be appriciated if you tell me why you
think so.

Thank you.