Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751374AbdGMLTR (ORCPT <rfc822;w@1wt.eu>);
        Thu, 13 Jul 2017 07:19:17 -0400
Received: from mail-vk0-f65.google.com ([209.85.213.65]:36519 "EHLO
        mail-vk0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1750854AbdGMLTQ (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 13 Jul 2017 07:19:16 -0400
MIME-Version: 1.0
In-Reply-To: <20170713102905.ysrvn7td6ryt4jaj@hirez.programming.kicks-ass.net>
References: <1495616389-29772-1-git-send-email-byungchul.park@lge.com>
 <1495616389-29772-7-git-send-email-byungchul.park@lge.com>
 <20170711161232.GB28975@worktop> <20170712020053.GB20323@X58A-UD3R>
 <20170712075617.o2jds2giuoqxjqic@hirez.programming.kicks-ass.net>
 <20170713020745.GG20323@X58A-UD3R> <20170713081442.GA439@worktop>
 <20170713085746.GH20323@X58A-UD3R> <20170713095052.dssev34f7c43vlok@hirez.programming.kicks-ass.net>
 <20170713100953.GI20323@X58A-UD3R> <20170713102905.ysrvn7td6ryt4jaj@hirez.programming.kicks-ass.net>
From: Byungchul Park <max.byungchul.park@gmail.com>
Date: Thu, 13 Jul 2017 20:19:14 +0900
Message-ID: <CANrsvRNAeL=Xdrbg5k56o5pC_p05LN7=rSrXLTHBJiXXFXk5Mw@mail.gmail.com>
Subject: Re: [PATCH v7 06/16] lockdep: Detect and handle hist_lock ring buffer overwrite
To: Peter Zijlstra <peterz@infradead.org>
Cc: Byungchul Park <byungchul.park@lge.com>,
        Ingo Molnar <mingo@kernel.org>, tglx@linutronix.de,
        Michel Lespinasse <walken@google.com>, boqun.feng@gmail.com,
        kirill@shutemov.name,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org,
        npiggin@gmail.com, kernel-team@lge.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2035
Lines: 68

On Thu, Jul 13, 2017 at 7:29 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Jul 13, 2017 at 07:09:53PM +0900, Byungchul Park wrote:
>> On Thu, Jul 13, 2017 at 11:50:52AM +0200, Peter Zijlstra wrote:
>> >     wait_for_completion(&C);
>> >       atomic_inc_return();
>> >
>> >                                     mutex_lock(A1);
>> >                                     mutex_unlock(A1);
>> >
>> >
>> >                                     <IRQ>
>> >                                       spin_lock(B1);
>> >                                       spin_unlock(B1);
>> >
>> >                                       ...
>> >
>> >                                       spin_lock(B64);
>> >                                       spin_unlock(B64);
>> >                                     </IRQ>
>> >
>> >
>> >                                     mutex_lock(A2);
>> >                                     mutex_unlock(A2);
>> >
>> >                                     complete(&C);
>> >
>> >
>> > That gives:
>> >
>> >     xhist[ 0] = A1
>>
>> We have to rollback here later on irq_exit.
>>
>> The followings are ones for irq context.
>>
>> >     xhist[ 1] = B1
>> >     ...
>> >     xhist[63] = B63
>> >
>> > then we wrap and have:
>> >
>> >     xhist[0] = B64
>> >
>> > then we rewind to 1 and invalidate to arrive at:
>> >
>>
>> Now, whether xhist[0] has been overwritten or not is important. If yes,
>> xhist[0] should be NULL, _not_ xhist[1], which is one for irq context so
>> not interest at all.
>>
>> >     xhist[ 0] = B64
>> >     xhist[ 1] = NULL   <-- idx
>>
>> Therefore, it should be,
>>
>>       xhist[ 0] = NULL <- invalidate, cannot use it any more
>>       --- <- on returning back from irq context, start from here
>>       xhist[ 1] = B1 <-- obsolete history of irq
>
> Ah, so you rely on the same_context_xhlock() ? That doesn't work for
> hist (formerly work).

As I mentioned in cover-letter, I applied the rollback mechanism into work
(of workqueue) as well. So it works even for hist.

-- 
Thanks,
Byungchul