Re: [patch 5/8] hrtimer remove state field

[Thomas Gleixner <tglx@linutronix.de>]

Roman,

I looked up the exact problem again.

On Sun, 2006-03-12 at 14:26 +0100, Roman Zippel wrote:
> > softirq runs on CPU0
> > base->lock()
> > 
> > remove_timer(timer);
> > 
> > base->unlock()
> > 			signal of previous expiry is delivered on CPU1
> > 			timer is reqeued.

		------->  sig_ignore is set

> > requeue = timer->fn();
> > 
> > base->lock()
> > 
> > if (requeue)
> > 	enqueue_timer(timer)
> > 
> > --> OOPS
> > 
> > We can not wait in the signal delivery path until the callback has been
> > executed, as we hold the posix-timer->lock and this would deadlock
> > timer->fn().
> 
> posix_timer either restarts the timer directly or via signal delivery, but 
> never both, so this case can't happen (unless there is a bug in the 
> posix_timer).

It took quite a time to track this down. Its unlikely, but it _CAN_
happen !

	tglx


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