Re: [patch 2/2] hrtimer

[Roman Zippel <zippel@linux-m68k.org>]

Hi,

On Tue, 28 Mar 2006, Oleg Nesterov wrote:

> I also think this is racy.
> 
> CPU_0					CPU_1
> 
> hrtimer_wakeup:
> 
> 	task = t->task;
> 	t->task = NULL;
> 
> 	<--- INTERRUPT --->
> 
> 					task is woken by signal,
> 					do_nanosleep() sees t->task == NULL,
> 					returns without hrtimer_cancel(),
> 					and __exits__.
> 
> 	<--- RESUME --->
> 
> 	wake_up_process(task);
> 
> Instead of exit(), 'task' can go to TASK_STOPPED or TASK_UNINTERRUPTIBLE
> after return from do_nanosleep(), it will be awakened by hrtimer_wakeup()
> unexpectedly.

Indeed and my original patch did call hrtimer_cancel() unconditionally to 
synchronize with a possibly running timer.
Thomas, could you please document it a bit better, when you modify my 
patches?

bye, Roman
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