watchdog pet in kernel module

[Peter Teoh]

Hi Vipul,

I have seen this in a number of commercial software running on RHEL, and on
other realtime OS as well.   The watchdog mechanism is always working in
pair:   userspace "feeding" the dog (in the kernel).   (btw, feed the dog
is a more usually used term than "pet" the dog.   sorry for that.   google
for that and perhaps you can get more info?).

Like Valdis said, this way you will know when userspace hang, which is the
key criteria for reboot.   Why do u want to detect if the kernel hang
(versus busy doing something)?   Theoretically that is not possible,
especially when all interrupt are disabled.



On Wed, Dec 4, 2013 at 6:45 AM, Vipul Jain <vipulsj at gmail.com> wrote:

>
>
>
> On Tue, Dec 3, 2013 at 2:31 PM, <Valdis.Kletnieks at vt.edu> wrote:
>
>> On Tue, 03 Dec 2013 13:15:32 -0800, Vipul Jain said:
>>
>> > currently we configure/pet the watchdog from user space via /dev/ipmi0
>> > device interface and I would like to do the pet part from kernel module.
>>
>> That's actually defeating the purpose.  If you do it from the kernel,
>> you keep the watchdog from detecting a whole set of hangs that can cause
>> userspace to wedge up.
>>
>
> Well we use different mechanism to detect user space hangs and take
> corrective actions. Hence we want to separate the user space issues from
> kernel space issues by using hardware watchdog pet in kernel space.
>
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-- 
Regards,
Peter Teoh
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