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

Guilherme G. Piccoli
2022-05-16T15:07:34Z

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