watchdog pet in kernel module

[Rajat Sharma]

Although /dev/watchdog is available in usermode, but nothing should stop
you to write to it from a kernel thread.

Rajat


On Wed, Dec 4, 2013 at 5:50 PM, Peter Teoh <htmldeveloper at gmail.com> wrote:

>
>
>
> On Thu, Dec 5, 2013 at 9:06 AM, Vipul Jain <vipulsj at gmail.com> wrote:
>
>>
>>
>>
>> On Wed, Dec 4, 2013 at 4:57 PM, <Valdis.Kletnieks at vt.edu> wrote:
>>
>>> On Wed, 04 Dec 2013 16:45:44 -0800, Vipul Jain said:
>>>
>>> > If you don't mind can you please provide me more insight as what can be
>>> > false alarm I can encounter to move pet inside kernel module?
>>>
>>> The issue isn't false alarms - it's failure to alarm when it should.
>>>
>>> The problem is that it's possible for a kernel to get wedged in such a
>>> way that
>>> a kernel thread is still able to feed the watchdog timer on a regular
>>> basis,
>>> but userspace is effectively hung and unable to proceed.  For example,
>>> if an
>>> OOPS happens while a filesystem lock is held, all future userspace
>>> references
>>> to that filesystem (and possibly all filesystems of the same type) will
>>> hang,
>>> eventually strangling the box while the kernel is still perfectly able
>>> to keep
>>> the watchdog working.
>>>
>>> Hi Valdis,
>>
>> I see what you are saying but what if the user process that's feeding the
>> dog gets hung and rest of the system is fine then it will bring the whole
>> system down won't it? I basically want to avoid this?
>>
>>
> Normally the process that feed the dog, is a simple process that JUST
> periodically set the watchdog device descriptor.    Yes, one main() with a
> while loop just periodically resetting the descriptor.
>
> And so it is is not able to respond in time, by inference, OTHER PROCESS
> must have hung.   In other system i saw there is a mother process that
> monitor a few (not all) of its key child process .... so perhaps one child
> will have one variable to signal to the mother that it is running.   If not
> responding in time, the mother will clean up everything and then purposely
> not setting the watchdog, resulting in reboot.
>
>
>> Regards,
>> Vipul.
>>
>>
>
>
> --
> Regards,
> Peter Teoh
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20131204/9c8b2540/attachment.html