watchdog pet in kernel module
fs.rajat at gmail.com
Wed Dec 4 21:19:03 EST 2013
Although /dev/watchdog is available in usermode, but nothing should stop
you to write to it from a kernel thread.
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
>>> but userspace is effectively hung and unable to proceed. For example,
>>> if an
>>> OOPS happens while a filesystem lock is held, all future userspace
>>> to that filesystem (and possibly all filesystems of the same type) will
>>> 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.
> Peter Teoh
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
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