On 02/08/22 at 03:51pm, Guilherme G. Piccoli wrote:
> On 28/01/2022 10:38, Petr Mladek wrote:
> > [...] On Thu 2022-01-27 14:16:20, Guilherme G. Piccoli wrote:
> > First, I am sorry for the very long mail. But the problem is really
> > complicated. I did my best to describe it a clean way.
> >
> > I have discussed these problems with a colleague and he had some good
> > points. And my view evolved even further.
>
> Thanks Petr for the very comprehensive and detailed email - this helps a
> lot in shaping the future of panic notifier(s)!
>
>
> > [...]
> > I think about the following solution:
> >
> > + split the notifiers into three lists:
> >
> > + info: stop watchdogs, provide extra info
> > + hypervisor: poke hypervisor
> > + reboot: actions needed only when crash dump did not happen
> >
> > + allow to call hypervisor notifiers before or after kdump
> >
> > + stop CPUs before kdump when either hypervisor notifiers or
> > kmsg_dump is enabled
> >
> > Note that it still allows to call kdump as the first action when
> > hypervisor notifiers are called after kdump and no kmsg dumper
> > is registered.
> >
> >
> > void panic(void)
> > {
> > [...]
> >
> > if (crash_kexec_post_hypervisor || panic_print || enabled_kmsg_dump()) {
> > /*
> > * Stop CPUs when some extra action is required before
> > * crash dump. We will need architecture dependent extra
> > * works in addition to stopping other CPUs.
> > */
> > crash_smp_send_stop();
> > cpus_stopped = true;
> > }
> >
> > if (crash_kexec_post_hypervisor) {
> > /* Tell hypervisor about the panic */
> > atomic_notifier_call_chain(&panic_hypervisor_notifier_list, 0, buf);
> > }
> >
> > if (enabled_kmsg_dump) {
> > /*
> > * Print extra info by notifiers.
> > * Prevent rumors, for example, by stopping watchdogs.
> > */
> > atomic_notifier_call_chain(&panic_info_notifier_list, 0, buf);
> > }
> >
> > /* Optional extra info */
> > panic_printk_sys_info();
> >
> > /* No dumper by default */
> > kmsg_dump();
> >
> > /* Used only when crash kernel loaded */
> > __crash_kexec(NULL);
> >
> > if (!cpus_stopped) {
> > /*
> > * Note smp_send_stop is the usual smp shutdown function, which
> > * unfortunately means it may not be hardened to work in a
> > * panic situation.
> > */
> > smp_send_stop();
> > }
> >
> > if (!crash_kexec_post_hypervisor) {
> > /* Tell hypervisor about the panic */
> > atomic_notifier_call_chain(&panic_hypervisor_notifier_list, 0, buf);
> > }
> >
> > if (!enabled_kmsg_dump) {
> > /*
> > * Print extra info by notifiers.
> > * Prevent rumors, for example, by stopping watchdogs.
> > */
> > atomic_notifier_call_chain(&panic_info_notifier_list, 0, buf);
> > }
> >
> > /*
> > * Help to reboot a safe way.
> > */
> > atomic_notifier_call_chain(&panic_reboot_notifier_list, 0, buf);
> >
> > [...]
> > }
> >
> > Any opinion?
> > Do the notifier list names make sense?
> >
>
> This was exposed very clearly, thanks. I agree with you, it's a good
> approach, and we can evolve that during the implementation phase, like
> "function A is not good in the hypervisor list because of this and
> that", so we move it to the reboot list. Also, name of the lists is not
> so relevant, might evolve in the implementation phase - I personally
> liked them, specially the "info" and "hypervisor" ones (reboot seems
> good but not great heh).
>
> So, what are the opinions from kdump maintainers about this idea?
> Baoquan / Vivek / Dave, does it make sense to you? Do you have any
> suggestions/concerns to add on top of Petr draft?
Yeah, it's reasonable. As I replied to Michael in another thread, I
think splitting the current notifier list is a good idea. At least the
code to archieve hyper-V's goal with panic_notifier is a little odd and
should be taken out and execute w/o conditional before kdump, and maybe
some others Petr has combed out.
For those which will be switched on with the need of adding panic_notifier
or panic_print into cmdline, the heavy users like HATAYAMA and Masa can
help check.
For Petr's draft code, does it mean hyper-V need another knob to trigger
the needed notifiers? Will you go with the draft direclty? Hyper-V now
runs panic notifiers by default, just a reminder.
>
> I prefer this refactor than the filter, certainly. If nobody else
> working on that, I can try implementing that - it's very interesting.
> The only thing I'd like to have first is an ACK from the kdump
> maintainers about the general idea.
>
> Cheers,
>
>
> Guilherme
>
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