On Wed, 26 Sep 2007, Tejun Heo wrote:

quoted text
> >> Hmmm... I might be missing something here.  Who else can wake up a
> >> thread in uninterruptible sleep?
> > 
> > In principle, anything can.  There has never been any guarantee in the 
> > kernel that a task sleeping on a waitqueue will remain asleep until 
> > the waitqueue is signalled.  That's part of the reason why things like 
> > __wait_event() are coded as loops.
> 
> Hmmm... I always thought the queue was because the condition can change
> inbetween waking up and actually running.  For example, if the condition
> is !(queue empty), another task can enter the critical section and
> consume the element which triggered wake up before the woken up task do.

That's the other part of the reason for using a loop.  :-)

Alan Stern

-
unsubscribe notice
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/