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

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Date:   Sat, 22 Jan 2022 18:55:14 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:     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 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.)