Date:   Mon, 16 May 2022 12:06:17 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Petr Mladek <pmladek@...e.com>, David Gow <davidgow@...gle.com>,
        Evan Green <evgreen@...omium.org>,
        Julius Werner <jwerner@...omium.org>,
        Scott Branden <scott.branden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Sebastian Reichel <sre@...nel.org>, linux-pm@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     akpm@...ux-foundation.org, bhe@...hat.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-edac@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-um@...ts.infradead.org,
        linux-xtensa@...ux-xtensa.org, netdev@...r.kernel.org,
        openipmi-developer@...ts.sourceforge.net, rcu@...r.kernel.org,
        sparclinux@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, kernel-dev@...lia.com, kernel@...ccoli.net,
        halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, corbet@....net,
        d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com,
        dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrea Parri <parri.andrea@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Brian Norris <computersforpeace@...il.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        "David S. Miller" <davem@...emloft.net>,
        Dexuan Cui <decui@...rosoft.com>,
        Doug Berger <opendmb@...il.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Justin Chen <justinpopo6@...il.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Lee Jones <lee.jones@...aro.org>,
        Markus Mayer <mmayer@...adcom.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mihai Carabas <mihai.carabas@...cle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Paul Mackerras <paulus@...ba.org>, Pavel Machek <pavel@....cz>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Wang ShaoBo <bobo.shaobowang@...wei.com>,
        Wei Liu <wei.liu@...nel.org>,
        zhenwei pi <pizhenwei@...edance.com>
Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

Thanks for the review!

I agree with the blinking stuff, I can rework and add all LED/blinking
stuff into the loop list, it does make sense. I'll comment a bit in the
others below...

On 16/05/2022 11:01, Petr Mladek wrote:
> [...]
>> --- a/arch/mips/sgi-ip22/ip22-reset.c
>> +++ b/arch/mips/sgi-ip22/ip22-reset.c
>> @@ -195,7 +195,7 @@ static int __init reboot_setup(void)
>>  	}
>>  
>>  	timer_setup(&blink_timer, blink_timeout, 0);
>> -	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
>> +	atomic_notifier_chain_register(&panic_hypervisor_list, &panic_block);
> 
> This notifier enables blinking. It is not much safe. It calls
> mod_timer() that takes a lock internally.
> 
> This kind of functionality should go into the last list called
> before panic() enters the infinite loop. IMHO, all the blinking
> stuff should go there.
> [...] 
>> --- a/arch/mips/sgi-ip32/ip32-reset.c
>> +++ b/arch/mips/sgi-ip32/ip32-reset.c
>> @@ -145,7 +144,7 @@ static __init int ip32_reboot_setup(void)
>>  	pm_power_off = ip32_machine_halt;
>>  
>>  	timer_setup(&blink_timer, blink_timeout, 0);
>> -	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
>> +	atomic_notifier_chain_register(&panic_hypervisor_list, &panic_block);
> 
> Same here. Should be done only before the "loop".
> [...] 

Ack.


>> --- a/drivers/firmware/google/gsmi.c
>> +++ b/drivers/firmware/google/gsmi.c
>> @@ -1034,7 +1034,7 @@ static __init int gsmi_init(void)
>>  
>>  	register_reboot_notifier(&gsmi_reboot_notifier);
>>  	register_die_notifier(&gsmi_die_notifier);
>> -	atomic_notifier_chain_register(&panic_notifier_list,
>> +	atomic_notifier_chain_register(&panic_hypervisor_list,
>>  				       &gsmi_panic_notifier);
> 
> I am not sure about this one. It looks like some logging or
> pre_reboot stuff.
> 

Disagree here. I'm looping Google maintainers, so they can comment.
(CCed Evan, David, Julius)

This notifier is clearly a hypervisor notification mechanism. I've fixed
a locking stuff there (in previous patch), I feel it's low-risk but even
if it's mid-risk, the class of such callback remains a perfect fit with
the hypervisor list IMHO.


> [...] 
>> --- a/drivers/leds/trigger/ledtrig-activity.c
>> +++ b/drivers/leds/trigger/ledtrig-activity.c
>> @@ -247,7 +247,7 @@ static int __init activity_init(void)
>>  	int rc = led_trigger_register(&activity_led_trigger);
>>  
>>  	if (!rc) {
>> -		atomic_notifier_chain_register(&panic_notifier_list,
>> +		atomic_notifier_chain_register(&panic_hypervisor_list,
>>  					       &activity_panic_nb);
> 
> The notifier is trivial. It just sets a variable.
> 
> But still, it is about blinking and should be done
> in the last "loop" list.
> 
> 
>>  		register_reboot_notifier(&activity_reboot_nb);
>>  	}
>> --- a/drivers/leds/trigger/ledtrig-heartbeat.c
>> +++ b/drivers/leds/trigger/ledtrig-heartbeat.c
>> @@ -190,7 +190,7 @@ static int __init heartbeat_trig_init(void)
>>  	int rc = led_trigger_register(&heartbeat_led_trigger);
>>  
>>  	if (!rc) {
>> -		atomic_notifier_chain_register(&panic_notifier_list,
>> +		atomic_notifier_chain_register(&panic_hypervisor_list,
>>  					       &heartbeat_panic_nb);
> 
> Same here. Blinking => loop list.

Ack.


>> [...]
>> diff --git a/drivers/misc/bcm-vk/bcm_vk_dev.c b/drivers/misc/bcm-vk/bcm_vk_dev.c
>> index a16b99bdaa13..d9d5199cdb2b 100644
>> --- a/drivers/misc/bcm-vk/bcm_vk_dev.c
>> +++ b/drivers/misc/bcm-vk/bcm_vk_dev.c
>> @@ -1446,7 +1446,7 @@ static int bcm_vk_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>>  
>>  	/* register for panic notifier */
>>  	vk->panic_nb.notifier_call = bcm_vk_on_panic;
>> -	err = atomic_notifier_chain_register(&panic_notifier_list,
>> +	err = atomic_notifier_chain_register(&panic_hypervisor_list,
>>  					     &vk->panic_nb);
> 
> It seems to reset some hardware or so. IMHO, it should go into the
> pre-reboot list.

Mixed feelings here, I'm looping Broadcom maintainers to comment.
(CC Scott and Broadcom list)

I'm afraid it breaks kdump if this device is not reset beforehand - it's
a doorbell write, so not high risk I think...

But in case the not-reset device can be probed normally in kdump kernel,
then I'm fine in moving this to the reboot list! I don't have the HW to
test myself.


> [...]
>> --- a/drivers/power/reset/ltc2952-poweroff.c
>> +++ b/drivers/power/reset/ltc2952-poweroff.c
>> @@ -279,7 +279,7 @@ static int ltc2952_poweroff_probe(struct platform_device *pdev)
>>  	pm_power_off = ltc2952_poweroff_kill;
>>  
>>  	data->panic_notifier.notifier_call = ltc2952_poweroff_notify_panic;
>> -	atomic_notifier_chain_register(&panic_notifier_list,
>> +	atomic_notifier_chain_register(&panic_hypervisor_list,
>>  				       &data->panic_notifier);
> 
> I looks like this somehow triggers the reboot. IMHO, it should go
> into the pre_reboot list.

Mixed feeling again here - CCing the maintainers for comments (Sebastian
/ PM folks).

This is setting a variable only, and once it's set (data->kernel_panic
is the bool's name), it just bails out the IRQ handler and a timer
setting - this timer seems kinda tricky, so bailing out ASAP makes sense
IMHO.

But my mixed feeling comes from the fact this notifier really is not a
fit to any list - it's just a "watchdog"/device quiesce in some form.
Since it's very low-risk (IIUC), I've put it here.


> [...]
>> --- 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).

Cheers,


Guilherme

Powered by blists - more mailing lists