Re: timer code oops when calling mod_delayed_work

From: Tejun Heo
Date: Tue Nov 03 2015 - 17:54:15 EST

Hello, Jeff.

On Tue, Nov 03, 2015 at 12:55:04PM -0500, Jeff Layton wrote:
> > Ok, I built a kernel with that patch reverted and that seems to fix the
> > problem.
> >
> > Looking at the patch, I guess the main difference is that we're no
> > longer using add_timer for unbound workqueue tasks. That said, we
> > should have possession of the PENDING bit before calling add_timer_on.
> >
> > So...I'm a little stumped. Any thoughts as to where the race could be?
> Ok, I've been able to reproduce this with a small module that I wrote
> as a reproducer:

I think I know what's going on. Looks like a bug in timer code when
timers are queued on a different cpu than before. Will experiment
with it a bit and report back.


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