Re: [RFC] [PATCH] Performance of del_timer_sync

[Ingo Molnar]

* Andrew Morton <akpm@xxxxxxxx> wrote:

> Ingo, why is this not sufficient?
> 
> @@ -331,6 +331,8 @@ int del_timer_sync(struct timer_list *ti
>  
>  del_again:
>  	ret += del_timer(timer);
> +	if (!ret)
> +		return 0;
>  
>  	for_each_cpu(i) {
>  		base = &per_cpu(tvec_bases, i);

it's not sufficient because a timer might be running on another CPU even
if it has not been deleted. We delete a timer prior running it (so that
the timer fn can re-activate the timer). So del_timer_sync() has to
synchronize independently of whether the timer was removed or not.

	Ingo
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