linux-kernel - Re: [PATCH v2 4/4] sched/fair: Abort wakeup when task is no longer in a sleeping state

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Date:	Sat, 13 Feb 2016 13:09:53 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ding Tianhong <dingtianhong@...wei.com>,
	Jason Low <jason.low2@....com>,
	Davidlohr Bueso <dave@...olabs.net>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <Will.Deacon@....com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH v2 4/4] sched/fair: Abort wakeup when task is no longer
 in a sleeping state

On Fri, Feb 12, 2016 at 04:22:29PM -0500, Waiman Long wrote:

> >>+	smp_cond_acquire(!p->on_cpu || !(p->state&  state));
> >>+	if (!(p->state&  state)) {
> >>+		success = 0;
> >>+		goto out;
> >>+	}
> >This doesn't make sense, if we managed to get here, p->on_rq must be
> >false, which means the other side is already in the middle of
> >schedule().
> Yes, you are right. It is my bad that I miss the on_rq check earlier. Just
> scrap the last patch.

No worries, that is tricky code :-)