linux-kernel - Re: [patch 01/19] hrtimers: state tracking

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Date:	Fri, 10 Nov 2006 01:40:53 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Len Brown <lenb@...nel.org>, John Stultz <johnstul@...ibm.com>,
	Andi Kleen <ak@...e.de>, Roman Zippel <zippel@...ux-m68k.org>
Subject: Re: [patch 01/19] hrtimers: state tracking

On Fri, 10 Nov 2006 10:19:48 +0100
Arjan van de Ven <arjan@...radead.org> wrote:

> 
> > +/*
> > + * Bit values to track state of the timer
> > + *
> > + * Possible states:
> > + *
> > + * 0x00		inactive
> > + * 0x01		enqueued into rbtree
> > + * 0x02		callback function running
> > + * 0x03		callback function running and enqueued
> > + *		(was requeued on another CPU)
> > + *
> > + * The "callback function running and enqueued" status is only possible on
> > + * SMP. It happens for example when a posix timer expired and the callback
> > + * queued a signal. Between dropping the lock which protects the posix timer
> > + * and reacquiring the base lock of the hrtimer, another CPU can deliver the
> > + * signal and rearm the timer. We have to preserve the callback running state,
> > + * as otherwise the timer could be removed before the softirq code finishes the
> > + * the handling of the timer.
> > + *
> > + * The HRTIMER_STATE_ENQUEUE bit is always or'ed to the current state to
> > + * preserve the HRTIMER_STATE_CALLBACK bit in the above scenario.
> > + *
> > + * All state transitions are protected by cpu_base->lock.
> > + */
> > +#define HRTIMER_STATE_INACTIVE	0x00
> > +#define HRTIMER_STATE_ENQUEUED	0x01
> > +#define HRTIMER_STATE_CALLBACK	0x02
> 
> where is the define for 0x03?
> 
> >  
> > +static inline int hrtimer_is_queued(struct hrtimer *timer)
> > +{
> > +	return timer->state != HRTIMER_STATE_INACTIVE &&
> > +		timer->state != HRTIMER_STATE_CALLBACK;
> > +}
> 
> the state things are either bits or they're not. If they're bits, you
> probably want to make this a bitcheck instead...
> >  	rb_insert_color(&timer->node, &base->active);
> > +	/*
> > +	 * HRTIMER_STATE_ENQUEUED is or'ed to the current state to preserve the
> > +	 * state of a possibly running callback.
> > +	 */
> > +	timer->state |= HRTIMER_STATE_ENQUEUED;
> 
> ok so it IS a bit thing, see comment about hrtimer_is_queued() not being
> a bit check then...
> 

eek.  I exhaustively went over that confusion in my initial (and lengthy)
review of these patches.

I don't think we ever saw a point-by-point reply.  What got lost?
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