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SubjectIRQ and sleep_on
I've missed the thread "avoiding bad sleeps" last week. I've had a similar problem and I would like to discuss the solution I've used to avoid it.

I want to wake up a sleeping process from an IRQ handler. In the process, if I use a interruptible_sleep_on(), I need first to restore flags (otherwise the process will sleep forever).

restore_flags(flags);
// <<== here IRQ handler possibly call wake_up()
interruptible_sleep_on(&my_queue);

If I first enable interrupts and then call sleep_on, sometimes (often) the wake_up is called (due to a pending interrupt) when the wait_queue is empty.
I've written a modified version of interruptible_sleep_on which takes an additionnal argument : flags to be restored.

my_interruptible_sleep_on(&my_queue, flags);

It seems to be ok. I've no more bad sleeps or more exactly rarely and that why I submit this to you. Is my way to do it correct ?
I've joined at the end of this mail the modified function.

Thanks,
Christophe Barbé

long my_interruptible_sleep_on_timeout(struct wait_queue **p, long timeout, unsigned long oflags)
{
unsigned long flags;
struct wait_queue wait;
current->state = TASK_INTERRUPTIBLE;

// SLEEP_ON_HEAD
wait.task = current;
write_lock_irq(&waitqueue_lock);
__add_wait_queue(p, &wait);
write_unlock(&waitqueue_lock);

restore_flags(oflags);
timeout = schedule_timeout(timeout);

// SLEEP_ON_TAIL
write_lock_irqsave(&waitqueue_lock,flags);
__remove_wait_queue(p, &wait);
write_unlock_irqrestore(&waitqueue_lock,flags);

return timeout;
}
--
Christophe Barbé
Software Engineer
Lineo High Availability Group
42-46, rue Médéric
92110 Clichy - France
phone (33).1.41.40.02.12
fax (33).1.41.40.02.01
www.lineo.com
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