[PATCH 1/3] panic: Disable crash_kexec_post_notifiers if kdump is not available
vgoyal at redhat.com
Tue Jul 14 11:23:36 PDT 2015
On Tue, Jul 14, 2015 at 01:01:12PM -0500, Eric W. Biederman wrote:
> Vivek Goyal <vgoyal at redhat.com> writes:
> > On Tue, Jul 14, 2015 at 05:29:53PM +0000, dwalker at fifo99.com wrote:
> > [..]
> >> > >> > If a machine is failing, there are high chance it can't deliver you the
> >> > >> > notification. Detecting that failure suing some kind of polling mechanism
> >> > >> > might be more reliable. And it will make even kdump mechanism more
> >> > >> > reliable so that it does not have to run panic notifiers after the crash.
> >> > >>
> >> > >> I think what your suggesting is that my company should change how it's hardware works
> >> > >> and that's not really an option for me. This isn't a simple thing like checking over the
> >> > >> network if the machine is down or not, this is way more complex hardware design.
> >> > >
> >> > > That means you are ready to live with an unreliable design. There might be
> >> > > cases where notifier does not get run properly and you will not do switch
> >> > > despite the fact that OS has failed. I was just trying to nudge you in
> >> > > a direction which could be more reliable mechanism.
> >> >
> >> > Sigh I see some deep confusion going on here.
> >> >
> >> > The panic notifiers are just that panic notifiers. They have not been
> >> > nor should they be tied to kexec. If those notifiers force a switch
> >> > over of between machines I fail to see why you would care if it was
> >> > kexec or another panic situation that is forcing that switchover.
> >> Hidehiro isn't fixing the failover situation on my side, he's fixing register
> >> information collection when crash_kexec_post_notifiers is used.
> > Sure. Given that we have created this new parameter, let us fix it so that
> > we can capture the other cpu register state in crash dump.
> > I am little disappointed that it was not tested well when this parameter was
> > introuced. We should have atleast tested it to the extent to see if there
> > is proper cpu state present for all cpus in the crash dump.
> > At that point of time it looked like a simple modification
> > to allow panic notifiers before crash_kexec().
> Either that or we say no one cares enough, and it known broken so let's
> just revert the fool thing.
Masami, you introduced this option. Are you fine with the revert? Is it
really being used and tested?
> I honestly can't see how to support panic notifiers, before kexec.
> There is no way to tell what is being done and all of the pieces
> including smp_send_stop are known to be buggy.
we should be able to replace smp_send_stop() with what crash_kexec() is
doing to stop the machine? If yes, then it should be fine I guess. This
parameter description clearly says that specify it at your own risk. So
we are not issuing a big support statement for successful kdump after
panic notifiers. If it is something fixable, otherwise user needs
to deal with it.
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