Messages in this thread |  | | | Date | Fri, 11 Mar 2005 21:54:17 +0300 | | From | Oleg Nesterov <> | | Subject | Re: [patch] del_timer_sync scalability patch |
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Hello.
I am not sure, but I think this patch incorrect.
> @@ -466,6 +482,7 @@ repeat: > set_running_timer(base, timer); > smp_wmb(); > timer->base = NULL; ------> WINDOW <------ > + set_last_running(timer, base); > spin_unlock_irq(&base->lock);
Suppose it is the first invocation of timer, so timer->last_running == NULL.
What if del_timer_sync() happens in that window?
del_timer_sync: del_timer(); // timer->base == NULL, returns base = timer->last_running; if (base) // no, it is still NULL ... if (timer->base != NULL || timer->last_running != base) goto del_again; // not taken return;
I think it is not enough to exchange these 2 lines in __run_timers, we also need barriers.
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