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

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Date:   Fri, 16 Aug 2019 21:41:52 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alan Stern <stern@...land.harvard.edu>,
        rostedt <rostedt@...dmis.org>,
        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 16, 2019, at 6:57 PM, Linus Torvalds torvalds@...ux-foundation.org wrote:

> So in general, we very much expect the compiler to do sane code
> generation, and not (for example) do store tearing on normal
> word-sized things or add writes that weren't there originally etc.

My understanding of https://lwn.net/Articles/793253/ section "Store tearing"
which points at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56028 seems
to contradict your expectation at least when writing constants to a
64-bit word without a volatile access.

Thanks,

Mathieu


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