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Date:   Fri, 24 Jul 2020 10:55:42 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Chris Wilson <chris@chris-wilson.co.uk>, mingo@kernel.org,
        tglx@linutronix.de, linux-kernel@vger.kernel.org,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, frederic@kernel.org,
        torvalds@linux-foundation.org, hch@lst.de
Subject: Re: [PATCH -v2 1/5] sched: Fix ttwu() race
Message-ID: <20200724175542.GR9247@paulmck-ThinkPad-P72>
Reply-To: paulmck@kernel.org
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On Thu, Jul 23, 2020 at 10:11:28PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 23, 2020 at 08:41:03PM +0100, Chris Wilson wrote:
> 
> > I am very sorry for the wild goose chase.
> 
> *phew*... all good then. I was starting to go a little ga-ga trying to
> make sense of things.
> 
> Arguably we should probably do something like:
> 
> 
> @@ -4555,7 +4572,7 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
>  int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
>  			  void *key)
>  {
> -	return try_to_wake_up(curr->private, mode, wake_flags);
> +	return try_to_wake_up(curr->private, mode, wake_flags & WF_SYNC);
>  }
>  EXPORT_SYMBOL(default_wake_function);

If you do:

Tested-by: Paul E. McKenney <paulmck@kernel.org>

This was about nine hours of each of the default rcutorture scenarios.

							Thanx, Paul

> Since I don't think anybody uses anything other than WF_SYNC, ever. And
> the rest of the WF_flags are used internally.
> 
> Thanks Chris!