Messages in this thread |  | | | Date | Tue, 29 Nov 2005 15:57:59 +0300 | | From | Oleg Nesterov <> | | Subject | Re: [PATCH 1/9] timer locking optimization |
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Roman Zippel wrote: > > + base = timer->base; > + spin_lock_irqsave(&base->lock, *flags); > + while (unlikely(base != timer->base)) { > + /* The timer has migrated to another CPU */ > + spin_unlock(&base->lock); > cpu_relax(); > + base = timer->base; > + spin_lock(&base->lock);
This spins with interrupts disabled, not good, imho.
> int __mod_timer(struct timer_list *timer, unsigned long expires) > @@ -212,6 +207,7 @@ int __mod_timer(struct timer_list *timer > > base = lock_timer_base(timer, &flags); > > +restart: > if (timer_pending(timer)) { > detach_timer(timer, 0); > ret = 1; > @@ -231,11 +227,16 @@ int __mod_timer(struct timer_list *timer > /* The timer remains on a former base */ > new_base = container_of(base, tvec_base_t, t_base); > } else { > - /* See the comment in lock_timer_base() */ > - timer->base = NULL; > + /* > + * We shortly release the timer and the timer can > + * migrate to another cpu, so recheck the base after > + * getting the lock. > + */ > + timer->base = &new_base->t_base; > spin_unlock(&base->lock); > spin_lock(&new_base->t_base.lock); > - timer->base = &new_base->t_base; > + if (unlikely(timer->base != &new_base->t_base)) > + goto restart;
This is not right.
This way you can delete the timer (ret == 1), notice that timer's base was changed after re-locking, goto restart, and get ret == 0.
Also, you have wrong value of 'base' after 'goto restart'.
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