linux-kernel - Re: [PATCH] ip2: avoid add

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Date:	Tue, 15 Jul 2008 12:06:39 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	"Michael H. Warfield" <mhw@...tsend.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] ip2: avoid add_timer() with pending timer

On Mon, Jul 14, 2008 at 10:04:02AM -0700, Andrew Morton wrote:
> On Mon, 14 Jul 2008 11:49:55 +0900 Akinobu Mita <akinobu.mita@...il.com> wrote:
> 
> > @@ -746,10 +742,8 @@ ip2_loadmain(int *iop, int *irqp)
> >  			}
> >  			if ( ip2config.irq[i] == CIR_POLL ) {
> >  retry:
> > -				if (!TimerOn) {
> > -					PollTimer.expires = POLL_TIMEOUT;
> > -					add_timer ( &PollTimer );
> > -					TimerOn = 1;
> > +				if (!timer_pending(&PollTimer)) {
> > +					mod_timer(&PollTimer, POLL_TIMEOUT);
> >  					printk( KERN_INFO "IP2: polling\n");
> 
> This change to ip2_loadmain() might be racy if it actually did
> anything.  But afaict timer_pending() can never be true here (we're
> only called from module_init()) so it can and should be removed.

Yes, ip2_loadmain() is only called from module_init(). But this add_timer()
is in the loop for each device. So it may be called more than once.

And yes, I can remove timer_pending() here because I switched to use
mod_timer() instead of add_timer(). But this PollTimer works as periodic
timer and it's global timer. So it will not cause a problem.

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