linux-kernel - Re: [PATCH v3] Fix lockup related to stop_machine being stuck in __do

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Message-ID: <51B60803.9020706@candelatech.com>
Date:	Mon, 10 Jun 2013 10:08:19 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org, eric.dumazet@...il.com,
	stable@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [PATCH v3] Fix lockup related to stop_machine being stuck in
 __do_softirq.

On 06/06/2013 02:40 PM, Tejun Heo wrote:
> On Thu, Jun 06, 2013 at 02:29:49PM -0700, greearb@...delatech.com wrote:
>> From: Ben Greear <greearb@...delatech.com>
>>
>> The stop machine logic can lock up if all but one of
>> the migration threads make it through the disable-irq
>> step and the one remaining thread gets stuck in
>> __do_softirq.  The reason __do_softirq can hang is
>> that it has a bail-out based on jiffies timeout, but
>> in the lockup case, jiffies itself is not incremented.
>>
>> To work around this, re-add the max_restart counter in __do_irq
>> and stop processing irqs after 10 restarts.
>>
>> Thanks to Tejun Heo and Rusty Russell and others for
>> helping me track this down.
>>
>> This was introduced in 3.9 by commit:  c10d73671ad30f5469
>> (softirq:  reduce latencies).
>>
>> It may be worth looking into ath9k to see if it has issues with
>> it's irq handler at a later date.
>>
>> The hang stack traces look something like this:
> ...
>> Signed-off-by: Ben Greear <greearb@...delatech.com>
>
>   Acked-by: Tejun Heo <tj@...nel.org>
>
> Linus, while this doesn't fix the root cause of the problem - softirq
> runaway - I still think this is a worthwhile protection to have.  Ben
> is in the process of finding out why the softirq runaway happens in
> the first place.  We probably want to add Cc: stable@...r.kernel.org
> tag.

This patch does not seem to be in mainline yet.

Do I need to do something else, or just be patient?

Thanks,
Ben

>
> Thanks.
>


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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