linux-kernel - Re: [PATCH V4] notifier/panic: Introduce panic_notifier

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Date:   Sun, 23 Jan 2022 22:07:11 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
        Petr Mladek <pmladek@...e.com>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, dyoung@...hat.com,
        linux-doc@...r.kernel.org, vgoyal@...hat.com,
        stern@...land.harvard.edu, akpm@...ux-foundation.org,
        andriy.shevchenko@...ux.intel.com, corbet@....net,
        halves@...onical.com, kernel@...ccoli.net,
        Will Deacon <will@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        John Ogness <john.ogness@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>, mikelley@...rosoft.com
Subject: Re: [PATCH V4] notifier/panic: Introduce panic_notifier_filter

On Sat, 22 Jan 2022 18:55:14 +0800
Baoquan He <bhe@...hat.com> wrote:

> On 01/21/22 at 05:31pm, Guilherme G. Piccoli wrote:
> ......
> > > IMHO, the right solution is to split the callbacks into 2 or more
> > > notifier list. Then we might rework panic() to do:
> > > 
> > > void panic(void)
> > > {
> > > 	[...]
> > > 
> > > 	/* stop watchdogs + extra info */
> > > 	atomic_notifier_call_chain(&panic_disable_watchdogs_notifier_list, 0, buf);
> > > 	atomic_notifier_call_chain(&panic_info_notifier_list, 0, buf);
> > > 	panic_print_sys_info();
> > > 
> > > 	/* crash_kexec + kmsg_dump in configurable order */
> > > 	if (!_crash_kexec_post_kmsg_dump) {
> > > 		__crash_kexec(NULL);
> > > 		smp_send_stop();
> > > 	} else {
> > > 		crash_smp_send_stop();
> > > 	}
> > > 
> > > 	kmsg_dump();
> > > 	if (_crash_kexec_post_kmsg_dump)
> > > 		__crash_kexec(NULL);
> > > 
> > > 	/* infinite loop or reboot */
> > > 	atomic_notifier_call_chain(&panic_hypervisor_notifier_list, 0, buf);
> > > 	atomic_notifier_call_chain(&panic_rest_notifier_list, 0, buf);
> > > 
> > > 	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
> > > [...] 
> > > Two notifier lists might be enough in the above scenario. I would call
> > > them:
> > > 
> > > 	panic_pre_dump_notifier_list
> > > 	panic_post_dump_notifier_list
> > > 
> > > 
> > > It is a real solution that will help everyone. It is more complicated now
> > > but it will makes things much easier in the long term. And it might be done
> > > step by step:
> > > 
> > >      1. introduce the two notifier lists
> > >      2. convert all users: one by one
> > >      3. remove the original notifier list when there is no user
> > 
> > That's a great idea! I'm into it, if we have a consensus. The thing that
> > scares me most here is that this is a big change and consumes time to
> > implement - I'd not risk such time if somebody is really against that.
> > So, let's see more opinions, maybe the kdump maintainers have good input.
> 
> I am fine with it. As long as thing is made clear, glad to see code is
> refactored to be more understandable and improved. Earlier, during several
> rounds of discussion between you and Petr, seveal pitfalls have been
> pointed out and avoided.
> 
> Meanwhile, I would suggest Masa and HATAYAMA to help give input about
> panic_notifier usage and refactory. AFAIK, they contributed code and use
> panic_notifier in their product or environment a lot, that will be very
> helpful to get the first hand information from them.
> 
> Hi Masa, HATAYANA,
> 
> Any comment on this? (Please ignore this if it's not in your care.)

No, that looks good idea to me. BTW, the 'dump' in the new notifieers
means both kmsg_dump and crash dump, right?

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>