linux-kernel - Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

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Message-ID: <YoSnGmBJ3kYs5WMf@alley>
Date:   Wed, 18 May 2022 09:58:18 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
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Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

On Tue 2022-05-17 15:57:34, Petr Mladek wrote:
> On Mon 2022-05-16 12:06:17, Guilherme G. Piccoli wrote:
> > >> --- a/drivers/soc/bcm/brcmstb/pm/pm-arm.c
> > >> +++ b/drivers/soc/bcm/brcmstb/pm/pm-arm.c
> > >> @@ -814,7 +814,7 @@ static int brcmstb_pm_probe(struct platform_device *pdev)
> > >>  		goto out;
> > >>  	}
> > >>  
> > >> -	atomic_notifier_chain_register(&panic_notifier_list,
> > >> +	atomic_notifier_chain_register(&panic_hypervisor_list,
> > >>  				       &brcmstb_pm_panic_nb);
> > > 
> > > I am not sure about this one. It instruct some HW to preserve DRAM.
> > > IMHO, it better fits into pre_reboot category but I do not have
> > > strong opinion.
> > 
> > Disagree here, I'm CCing Florian for information.
> > 
> > This notifier preserves RAM so it's *very interesting* if we have
> > kmsg_dump() for example, but maybe might be also relevant in case kdump
> > kernel is configured to store something in a persistent RAM (then,
> > without this notifier, after kdump reboots the system data would be lost).
> 
> I see. It is actually similar problem as with
> drivers/firmware/google/gsmi.c.

As discussed in the other other reply, it seems that both affected
notifiers do not store kernel logs and should stay in the "hypervisor".

> I does similar things like kmsg_dump() so it should be called in
> the same location (after info notifier list and before kdump).
>
> A solution might be to put it at these notifiers at the very
> end of the "info" list or make extra "dump" notifier list.

I just want to point out that the above idea has problems.
Notifiers storing kernel log need to be treated as kmsg_dump().
In particular, we would  need to know if there are any.
We do not need to call "info" notifier list before kdump
when there is no kernel log dumper registered.

Best Regards,
Petr