linux-kernel - Re: softlockups in multi_cpu

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Date:	Fri, 06 Mar 2015 17:53:26 -0800
From:	Jason Low <jason.low2@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...emonkey.org.uk>, jason.low2@...com
Subject: Re: softlockups in multi_cpu_stop

On Fri, 2015-03-06 at 13:24 -0800, Linus Torvalds wrote:
> On Fri, Mar 6, 2015 at 1:12 PM, Jason Low <jason.low2@...com> wrote:
> >
> > +       while (true) {
> > +               if (sem->owner != owner)
> > +                       break;
> 
> That looks *really* odd.
> 
> Why is this not
> 
>         while (sem->owner == owner) {

Yes, this looks more readable.

That while (true) thing was something we recently did for mutexes which
was why I originally had that.

> Also, this "barrier()" now lost the comment:
> 
> > +               barrier();
> 
> so it looks very odd indeed.

Right, we should keep the comment for the barrier().

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