linux-kernel - Re: [PATCH] cpuidle - fix lock contention in the idle path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <50E6764C.9060608@linaro.org>
Date:	Fri, 04 Jan 2013 07:27:24 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	rafael.j.wysocki@...el.com
CC:	Russ Anderson <rja@....com>, linux-pm@...r.kernel.org,
	pdeschrijver@...dia.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, rja@...ricas.sgi.com
Subject: Re: [PATCH] cpuidle - fix lock contention in the idle path

On 01/02/2013 10:13 PM, Russ Anderson wrote:
> On Wed, Dec 26, 2012 at 11:01:48AM +0100, Daniel Lezcano wrote:
>> The commit bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92 introduces
>> a lock in the cpuidle_get_cpu_driver function. This function
>> is used in the idle_call function.
>>
>> The problem is the contention with a large number of cpus because
>> they try to access the idle routine at the same time.
>>
>> The lock could be safely removed because of how is used the
>> cpuidle api. The cpuidle_register_driver is called first but
>> until the cpuidle_register_device is not called we don't
>> enter in the cpuidle idle call function because the device
>> is not enabled.
>>
>> The cpuidle_unregister_driver function, leading the a NULL driver,
>> is not called before the cpuidle_unregister_device.
>>
>> This is how is used the cpuidle api from the different drivers.
>>
>> However, a cleanup around the lock and a proper refcounting
>> mechanism should be used to ensure the consistency in the api,
>> like cpuidle_unregister_driver should failed if its refcounting
>> is not 0.
>>
>> These modifications will need some code reorganization and rewrite
>> which does not fit with a fix.
> 
> I agree.
> 
>> The following patch is a hot fix by returning to the initial behavior
>> by removing the lock when getting the driver.
> 
> The patch fixes the problem.  Verified on a system with 1024 cpus.
> Thanks.
> 
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> 
> Reported-by: Russ Anderson <rja@....com>
> Acked-by: Russ Anderson <rja@....com>

Hi Rafael,

could you consider this patch for merging ?

Thanks
  -- Daniel


-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/