Re: [PATCH v2] reboot: Backup orderly_poweroff

[Keerthy]

Hi Ingo,

On Tuesday 19 January 2016 02:36 PM, Ingo Molnar wrote:
> * Grygorii Strashko <grygorii.strashko@xxxxxx> wrote:
>
> > On 01/15/2016 12:14 PM, Ingo Molnar wrote:
> > > * One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > > > If kernel_power_off() is called then the system should power off. No ifs and
> > > > > whens.
> > > >
> > > > Even if it doesn't the watchdog should kill it.
> > > >
> > > > That is broken on some platforms on the watchdog side as the
> > > > watchdog shuts down during our power off callbacks - because the system
> > > > firmware is too stupid to reset the watchdog as it powers back up (so
> > > > keeps rebooting).
> > > >
> > > > If you watchdog and firmware function properly you shouldn't even have to
> > > > care if you crash during the kernel power off.
> > >
> > > That's a good point as well - if the system is 'stuck' for some notion of stuck,
> > > then watchdog drivers can help.
> >
> > Seems ARM doesn't have endless loop implemented in machine_power_off() - so,
> > not too much chances for Watchdog to fire.
> > void machine_power_off(void)
> > {
> > 	local_irq_disable();
> > 	smp_send_stop();
> >
> > 	if (pm_power_off)
> > 		pm_power_off();
> >
> > 	--- endless loop ?
> > 	--- or restart ?
> > }
> > [and even if it will be there - 20-30sec is usual timeout for Watchdog and this
> > enough time to burn the system in case of thermal emergency poweroff :(]
> >
> > > Here it's unclear whether user-space even called the sys_reboot() system call.
> >
> > That's true - original log [1] has
> > Nov 30 11:19:22 [    5.942769] thermal thermal_zone3: critical temperature reached(108 C),shutting down
> > [...]
> > Nov 30 11:19:24 [    7.387900] ahci 4a140000.sata: flags: 64bit ncq sntf stag pm led clo only pmp pio slum part ccc apst
> > Nov 30 11:19:24 INIT: Switching to runlevel: 0
> > Nov 30 11:19:24 INIT: Sending processes the TERM signal
> >
> > and there are no
> > [  220.004522] reboot: Power down
> >
> >
> > Also, It's not the first time this part of code is discussed (thermal emergency poweroff) [2],
> > so the good question, as for me, is it really required and safe to use orderly_poweroff() in
> > case of thermal emergency poweroff ([3] as example)?
> >
> > In general, this kind of use case can be simulated using SysRq on any arch
> > - [3.290034] Freeing unused kernel memory: 492K (c0a67000 - c0ae2000)
> >    INIT: version 2.88 booting
> >    Starting udev
> > ^^ The issue most probably might happens when system in the process of loading modules
> > So, once modules loading process is started - fire Sysrq "poweroff(o)"
>
> So I'd say emergency poweroff should be named accordingly - and the
> orderly_poweroff() name suggest anything but an emergency, right?
>
> So I'd be fine with the following:
>
>   - introduce a poweroff_emergency() core kernel function call
>
>   - use it in drivers where it's justified
>
>   - poweroff_emergency() has a configurable timeout value. If the timeout value is
>     set to 0 then it powers the system off immediately.
>
> Functionally it would be mostly equivalent to your current patch (except the '0'
> immediate poweroff functionality).

Thanks for the suggestion. I will work on this and get back.

Best Regards,
Keerthy

> Thanks,
>
> 	Ingo