lkml.org 
[lkml]   [2014]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 08/51] arm, hw-breakpoint: Fix CPU hotplug callback registration
Hi Srivatsa,

On Wed, Feb 05, 2014 at 10:06:04PM +0000, Srivatsa S. Bhat wrote:
> Subsystems that want to register CPU hotplug callbacks, as well as perform
> initialization for the CPUs that are already online, often do it as shown
> below:
>
> get_online_cpus();
>
> for_each_online_cpu(cpu)
> init_cpu(cpu);
>
> register_cpu_notifier(&foobar_cpu_notifier);
>
> put_online_cpus();
>
> This is wrong, since it is prone to ABBA deadlocks involving the
> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
> with CPU hotplug operations).

Hmm, the code in question (for this patch) runs from an arch_initcall. How
can you generate CPU hotplug operations at that stage?

> Instead, the correct and race-free way of performing the callback
> registration is:
>
> cpu_maps_update_begin();
>
> for_each_online_cpu(cpu)
> init_cpu(cpu);
>
> /* Note the use of the double underscored version of the API */
> __register_cpu_notifier(&foobar_cpu_notifier);
>
> cpu_maps_update_done();
>
>
> Fix the hw-breakpoint code in arm by using this latter form of callback
> registration.

I guess you introduce __register_cpu_notifier somewhere earlier in the
series, so it's best if you take this all via your tree.

Will


\
 
 \ /
  Last update: 2014-02-06 12:41    [W:1.309 / U:0.260 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site