On 03/06/22 at 11:21am, Guilherme G. Piccoli wrote:
> On 28/01/2022 10:38, Petr Mladek wrote:
> > [...]
> > 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?
> >
> > Best Regards,
> > Petr
>
>
> Hi folks, I'm working on this now, and while looking into it I've
> noticed that we have the concept of "priority" in the notifiers list.
> Basically, you can order the calls the way it fits best, priority is an
> integer and must the set in the moment of registration, it's up to the
> users of the notifiers to set it and enforce the ordering.
>
> So what I'm thinking is: currently, only 3 or 4 panic notifiers make use
> of that. What if, since we're re-working this, we add a priority for
> *all* notifiers and enforce its usage? This way we guarantee
> consistency, it'd make debug easier and maybe even more important:
> having all the notifiers and their priorities in a list present in the
> header file would be great documentation about all the existing
> notifiers and how they are called - today this information is quite
> obscure and requires lots of code grepping!
>
> Let me know your thoughts Petr / Baoquan - it would add slightly more
> code / complexity, but in my opinion the payback is very good.
> Cheers,
The ideal situation is each panic notifier has an order or index to
indicate its priority. Wondering how to make it. What I think of is
copying initcall. We have several priorities, at the same priority,
execution sequence is not important. Not sure if I get your point.
~~~~~~~
#define core_initcall(fn) __define_initcall(fn, 1)
#define core_initcall_sync(fn) __define_initcall(fn, 1s)
......
#define late_initcall(fn) __define_initcall(fn, 7)
#define late_initcall_sync(fn) __define_initcall(fn, 7s)
