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

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Message-ID: <20190817124337.6dd820a5@oasis.local.home>
Date:   Sat, 17 Aug 2019 12:43:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        David Howells <dhowells@...hat.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates

On Sat, 17 Aug 2019 11:53:41 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> kernel/trace/trace.c:tracing_record_taskinfo_sched_switch()
> kernel/trace/trace.c:tracing_record_taskinfo()
> 
> where @flags is used to control a few branches. I don't think any of those
> would end up causing corruption if the flags is re-fetched between two
> branches, but it seems rather fragile.

There shouldn't be any corruption, as each flag test is not dependent
on any of the other tests. But I do agree, a READ_ONCE() would be
appropriate for just making a consistent state among the tests, even
though they are independent.

-- Steve