On Wed, 21 Aug 2019, Sebastian Andrzej Siewior wrote: > 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. It _IS_ a problem when the base changes and the compiler reloads CPU0 CPU1 base = timer->base; lock(base->....); switch base reload base = timer->base; unlock(base->....); See?
