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Date: Mon, 30 Sep 2013 20:13:58 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>, Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/6] sched, wait: Collapse __wait_event macros -v4
Message-ID: <20130930181358.GA29544@redhat.com>
References: <20130930152242.207382649@infradead.org> <20130930174054.GA28129@redhat.com> <20130930180939.GN15690@laptop.programming.kicks-ass.net>
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On 09/30, Peter Zijlstra wrote:
>
> On Mon, Sep 30, 2013 at 07:40:54PM +0200, Oleg Nesterov wrote:
> > Once again, of course I do not blame this series, but
> > wait_event_timeout(wq, true, 0) still returns 0.
>
> So we have:
>
> [...snip...]

> So wait_event_timeout(wq, true, 0) turns into:

Not really, because of fast-path check,

	#define wait_event_timeout(wq, condition, timeout)			\
	({									\
		long __ret = timeout;						\
		if (!(condition)) 						\
			__ret = __wait_event_timeout(wq, condition, timeout);	\
		__ret;								\
	})

we do not even call __wait_event_timeout() if "condition" is already
true at the start.

> >  	___wait_event(wq, ___wait_cond_timeout(condition),		\
> >  		      TASK_INTERRUPTIBLE, 0, ret,	      		\
> >  		      spin_unlock_irq(&lock);				\
> > -		      __ret = schedule_timeout(__ret);			\
> > +		      ___wait_schedule_timeout(__ret);			\
> >  		      spin_lock_irq(&lock));
>
> You can't do that; you'll break/return without the lock held.

Yes, see another email, already noticed this.


And let me repeat just in case, I think this series is fine, just
wait.h needs another minor/orthogonal fix.

Oleg.