Don Zickus <dzickus at redhat.com> writes: > On Thu, Apr 18, 2013 at 09:35:05AM -0700, Eric W. Biederman wrote: >> Don Zickus <dzickus at redhat.com> writes: >> >> > A common problem with kdump is that during the boot up of the >> > second kernel, the hardware watchdog times out and reboots the >> > machine before a vmcore can be captured. >> > >> > Instead of tellling customers to disable their hardware watchdog >> > timers, I hacked up a hook to put in the kdump path that provides >> > one last kick before jumping into the second kernel. >> >> Having thought about this a little more this patch is actively wrong. >> >> The problem is you can easily be petting the watchdog in violation of >> whatever policy is normally in place. Which means that this extra >> petting can result in a system that is unavailable for an unacceptably >> long period of time. > > Not really, just an extra period which isn't that much. This would only > be noticable if kdump is setup and enabled and then _hung_, otherwise it > just quickly reboots and noone notices. :-) For the folks who care the definition of acceptable unavailability would look like: watchdog timeout + max boot time + margin of error. So it is possible for an extra watchdog pet to eat up or exceed your margin of error. You are more likely to cause a how in the world did that happen than something more extreme, but even playing invalidating peoples mental model can be a problem sometimes. >> I expect most watchdog policies are not that strict, but this patch >> would preclude using those that are. > > I would assume most of those users would not enable kdump and would not be > affected. I have seen it be the case that the goal is to record what went wrong if there is time, but to get back into service in a timely manner regardless. >> And like is being discussed in another subthread it does look like >> changing the timeout and the interval should be enough all on it's own. > > Probably and I will pursue that. Thanks for the suggestion. Eric
