lkml.org 
[lkml]   [2007]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 0/4] Refcount Based Cpu-Hotplug Revisit.
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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-17 04:15    [W:0.063 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site