Delaying an interrupt handler

[Milton Krutt]

> On Mon, Mar 23, 2015 at 2:18 PM, Milton Krutt <milton at krutt.org> wrote:
> > Hi.
> > It is known that no semaphore synchronization should be
> > used inside an interrupt handler.
> >
> > Anyway, I am looking at a freeBSD device driver (written by
> > a profesionist) and there are semaphores inside an interrupt
> > handler's subroutine.
> >
> > Since I should port to linux that driver, I ask you how can I
> > reach such synchronization under linux; I tried to use semaphores
> > inside my handler but I got complains, and I don't want to break
> > the law, so no semaphores for me.
> 
> Perhaps spinlocks could be the solution :).
> 
> 2.6.10 please no - :), Linux kernel is now at 4.0.
> 
> Daniel.

Yes and no. The routine the int. handler's delay depends on has to
make some non atomic work. So if I lock a spinlock and then I do some
"lengthy" (i.e. non atomic) job, then I get a warning message like
"spinlock held while being preempted" (or similar). In symbols, you suggest
something like

process P{

spin_lock(lock);
non_atomic_function();
spin_unlock(lock);

}

int. handler {

spin_lock(lock);
do_things(); /* preferably atomically */
spin_unlock(lock);

}

My first attempt is still to avoid both semaphores and the above remedy,
in order to delay the int. handler up to a desired point.

Thanks!