2017-08-18 15:40:39

by Sriram V

Subject: Kernel Panic sysrq questions

Hi,

1. I am testing my watchdog driver. The driver uses the internal
watchdog (Internal to SOC).
2. I use a single core SOC.
3. I have a workqueue which pets the watchdog every 60 seconds.
4. I trigger a kernel crash by doing a echo c > /proc/sysrq-trigger to
trigger a kernel crash
5. Even after the crash, I observe that the workqueue gets
periodically executed. (I have a printk
inside the workqueue before the pet as a result the watchdog does
not reset the board.

My Understanding is When a fatal panic happens, The Kernel is in
frozen state (no workques
or tasks get executed).

Is my understanding correct or am i missing something here.


Thanks,

Regards,
Sriram

2017-09-18 22:35:39

by Randy Dunlap

Subject: Re: Kernel Panic sysrq questions

On 08/18/17 08:40, Sriram V wrote:
> Hi,
>
> 1. I am testing my watchdog driver. The driver uses the internal
> watchdog (Internal to SOC).
> 2. I use a single core SOC.
> 3. I have a workqueue which pets the watchdog every 60 seconds.
> 4. I trigger a kernel crash by doing a echo c > /proc/sysrq-trigger to
> trigger a kernel crash
> 5. Even after the crash, I observe that the workqueue gets
> periodically executed. (I have a printk
> inside the workqueue before the pet as a result the watchdog does
> not reset the board.
>
> My Understanding is When a fatal panic happens, The Kernel is in
> frozen state (no workques
> or tasks get executed).
>
> Is my understanding correct or am i missing something here.

Hi,
What kernel version?

I don't see anything in the wq docs about that specific point.

Tejun?


--
~Randy

2017-09-19 00:23:12

by Tejun Heo

Subject: Re: Kernel Panic sysrq questions

Hello,

On Mon, Sep 18, 2017 at 03:35:36PM -0700, Randy Dunlap wrote:
> > My Understanding is When a fatal panic happens, The Kernel is in
> > frozen state (no workques
> > or tasks get executed).
> >
> > Is my understanding correct or am i missing something here.
>
> Hi,
> What kernel version?
>
> I don't see anything in the wq docs about that specific point.

There's nothing workqueue specific there. Panic doesn't bring the
system to a complete stop in general. If you wanna change how the
system behaves post-panic, please take a look at panic= boot param.

Thanks.

--
tejun