linux-kernel - Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates

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Message-ID: <1360102474.23943.1566057317249.JavaMail.zimbra@efficios.com>
Date:   Sat, 17 Aug 2019 11:55:17 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates

----- On Aug 17, 2019, at 11:26 AM, rostedt rostedt@...dmis.org wrote:

> On Sat, 17 Aug 2019 10:40:31 -0400 (EDT)
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
>> > I'm now even more against adding the READ_ONCE() or WRITE_ONCE().
>> 
>> I'm not convinced by your arguments.
> 
> Prove to me that there's an issue here beyond theoretical analysis,
> then I'll consider that patch.
> 
> Show me a compiler used to compile the kernel that zeros out the
> increment. Show me were the race actually occurs.
> 
> I think the READ/WRITE_ONCE() is more confusing than helpful. And
> unneeded churn to the code. And really not needed for something that's
> not critical to execution.

I'll have to let the authors of the LWN article speak up on this, because
I have limited time to replicate this investigation myself.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com