linux-kernel - Re: [PATCH -v2 1/5] sched: Fix ttwu() race

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Message-ID: <20200723201128.GT10769@hirez.programming.kicks-ass.net>
Date:   Thu, 23 Jul 2020 22:11:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, paulmck@...nel.org, frederic@...nel.org,
        torvalds@...ux-foundation.org, hch@....de
Subject: Re: [PATCH -v2 1/5] sched: Fix ttwu() race

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);


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!