Re: [RT PATCH 1/3] hrtimer: Use READ_ONCE to access timer->base in hrimer_grab_expiry_lock()

[Sebastian Andrzej Siewior]

On 2019-08-21 10:24:07 [+0100], Julien Grall wrote:
> The update to timer->base is protected by the base->cpu_base->lock().
> However, hrtimer_grab_expirty_lock() does not access it with the lock.
> 
> So it would theorically be possible to have timer->base changed under
> our feet. We need to prevent the compiler to refetch timer->base so the
> check and the access is performed on the same base.

It is not a problem if the timer's bases changes. We get here because we
want to help the timer to complete its callback.
The base can only change if the timer gets re-armed on another CPU which
means is completed callback. In every case we can cancel the timer on
the next iteration.

Sebastian