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Subject: Re: [patch 5/8] hrtimer remove state field
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Roman Zippel <zippel@linux-m68k.org>
Cc: Andrew Morton <akpm@osdl.org>, LKML <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>
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Date: Sun, 12 Mar 2006 15:54:45 +0100
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On Sun, 2006-03-12 at 15:30 +0100, Roman Zippel wrote:
> Hi,
> 
> On Sun, 12 Mar 2006, Thomas Gleixner wrote:
> 
> > > > > > base->unlock()
> > > > > > 			signal of previous expiry is delivered on CPU1
> > > > > > 			timer is reqeued.
> > > > 
> > > > 		------->  sig_ignore is set
> > > 
> > > ??? I can't find any symbol 'sig_ignore'.
> > 
> > Oh well. The application sets SIG_IGN for the signal in question, so
> > send_sigqueue() returns 1 because sig_ignored() returns 1.
> 
> In this case no signal is queued and the timer won't be restarted via 
> signal delivery.

Roman,

Interrupts are enable before fn() is called, so an interrupt can
actually delay it long enough that userspace on CPU1 can set SIG_IGN

CPU 0
spin_unlock_irq(base->lock)	
			CPU1
			signal is dequeued
				timer is requeued
			user space code is executed
			user space code sets SIG_IGN
restart = fn();

Now fn() calls send_sigqeue() which returns 1, resulting in ret =
HRTIMER_RESTART which leads to requeueing of an enqueued timer.

	tglx