linux-kernel - Re: [PATCH] perf: Fix race between close() and fork()

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Message-ID: <20190628204608.GG3402@hirez.programming.kicks-ass.net>
Date:   Fri, 28 Jun 2019 22:46:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        jolsa@...hat.com, dvyukov@...gle.com, namhyung@...nel.org,
        xiexiuqi@...wei.com,
        syzbot+a24c397a29ad22d86c98@...kaller.appspotmail.com
Subject: Re: [PATCH] perf: Fix race between close() and fork()

On Fri, Jun 28, 2019 at 05:50:03PM +0100, Mark Rutland wrote:
> > +		/*
> > +		 * Wake any perf_event_free_task() waiting for this event to be
> > +		 * freed.
> > +		 */
> > +		smp_mb(); /* pairs with wait_var_event() */
> > +		wake_up_var(var);
> 
> Huh, so wake_up_var() doesn't imply a RELEASE?
> 
> As an aside, doesn't that mean all callers of wake_up_var() have to do
> likewise to ensure it isn't re-ordered with whatever prior stuff they're
> trying to notify waiters about? Several do an smp_store_release() then a
> wake_up_var(), but IIUC the wake_up_var() could get pulled before that
> release...

Yah,...

  https://lkml.kernel.org/r/20190624165012.GH3436@hirez.programming.kicks-ass.net

I needs to get back to that.