Re: [PATCH 1/5] irq_work: Let arch tell us if it can raise irq work

Frederic Weisbecker
2014-05-13T19:33:41Z

On Tue, May 13, 2014 at 07:09:42PM +0200, Peter Zijlstra wrote:
> On Tue, May 13, 2014 at 04:38:37PM +0200, Frederic Weisbecker wrote:
> > We prepare for executing the full nohz kick through an irq work. But
> > if we do this as is, we'll run into conflicting tick locking: the tick
> > holds the hrtimer lock and the nohz kick may do so too.
>
> It does? How does the tick end up holding that lock?
>
> Normal hrtimer callbacks run without holding the hrtimer lock -- I made
> it so.
>
> This means tick_sched_timer() is called without hrtimer lock, and I
> don't see it taking it anywhere in tick_sched_do_timer() or
> tick_sched_handle().

Check hrtimer_interrupt(), it takes the per cpu base->lock.