Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code

From	Nikolay Borisov <kernel@kyup.com>
Newsgroups	linux.kernel
Subject	Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code
Date	2016-02-04 13:30 +0100
Message-ID	<qYrcR-7Z-3@gated-at.bofh.it> (permalink)
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On 02/04/2016 02:17 PM, Mike Galbraith wrote:
> On Thu, 2016-02-04 at 13:51 +0200, Nikolay Borisov wrote:
>>
>> On 02/04/2016 01:32 PM, Mike Galbraith wrote:
>>> On Wed, 2016-02-03 at 12:58 +0200, Nikolay Borisov wrote:
>>>>
>>>> So in this case the prev/next entries do not look like corrupted,
>>>> whereas
>>>> when manipulating the list inside detach_timer they do. This is
>>>> really
>>>> odd, any ideas how to further debug this?
>>>
>>> Suspiciously similar to https://lkml.org/lkml/2016/2/4/247
>>
>> Right, I've been cursory following this thread but I was left with the
>> impression this only occurs on machines where the CPU can go offline,
>> currently the server on which this happened should never offline any of
>> its CPUs since the power management is disabled (though I will have to
>> double check this).
> 
> AFAIU, hotplug isn't required, only mod_delayed_work() being called
> from a different CPU than where the timer was born, migrating it at a
> bad time.

Right, in this case the ib_addr was indeed using mod_delayed_work so
things line up so far.

> 
>> On a different note - is there a way to safely reproduce this so I can
>> test the suggested fix by Thomas?
> 
> Hm, write a module to beat mod_delayed_work() to pulp with a NR_CPUS
> horde, and run it in a vm where you don't care about shrapnel?

In other words, have multiple threads (NR_CPUS) that spin on
mod_delayed_work?


> 
> 	-Mike
>

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crash in 3.12.51 (likely in 3.12.52 as well) in timer code Nikolay Borisov <kernel@kyup.com> - 2016-02-03 12:00 +0100
  Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code Thomas Gleixner <tglx@linutronix.de> - 2016-02-04 10:00 +0100
  Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-02-04 12:40 +0100
    Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code Nikolay Borisov <kernel@kyup.com> - 2016-02-04 13:00 +0100
      Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-02-04 13:20 +0100
        Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-02-04 13:30 +0100
        Re: crash in 3.12.51 (likely in 3.12.52 as well) in timer code Nikolay Borisov <kernel@kyup.com> - 2016-02-04 13:30 +0100

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