On Tue, Oct 16, 2007 at 10:20:37AM -0700, Linus Torvalds wrote:
> On Tue, 16 Oct 2007, Gautham R Shenoy wrote:
>
> Well, afaik, the patch series is fairly clean, and I'm obviously perfectly
> happy with the approach, so I have no objections.
>
> But it looks buggy. This:
>
> +static void cpu_hotplug_begin(void)
> +{
> + mutex_lock(&cpu_hotplug.lock);
> + cpu_hotplug.active_writer = current;
> + while (cpu_hotplug.refcount) {
> + mutex_unlock(&cpu_hotplug.lock);
> + wait_for_completion(&cpu_hotplug.readers_done);
> + mutex_lock(&cpu_hotplug.lock);
> + }
> +
> +}
>
> drops the cpu_hotplug.lock, which - as far as I can see - means that
> another process can come in and do the same, and mess up the
> "active_writer" thing. The oerson that actually *gets* the lock may not be
> the same one that has "active_writer" set to itself. No? Am I missing
> something.
Unless I am reading the patch wrongly, it seems cpu_hotplug_begin() is called
while holding the cpu_add_remove_lock mutex. So, another CPU cannot come in
and do the same until _cpu_down() is over.
Thanks
Dipankar
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