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Date:   Thu, 13 May 2021 10:34:51 +0200
From:   Petr Mladek <pmladek@suse.com>
To:     "Vaittinen, Matti" <Matti.Vaittinen@fi.rohmeurope.com>
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Subject: Re: [PATCH v9 02/10] reboot: Add hardware protection power-off
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On Wed 2021-05-12 12:00:46, Vaittinen, Matti wrote:
> On Wed, 2021-05-12 at 10:20 +0200, Petr Mladek wrote:
> > On Mon 2021-05-10 14:28:30, Matti Vaittinen wrote:
> > > There can be few cases when we need to shut-down the system in
> > > order to
> > > protect the hardware. Currently this is done at east by the thermal
> > > core
> > > when temperature raises over certain limit.
> > > 
> > > Some PMICs can also generate interrupts for example for over-
> > > current or
> > > over-voltage, voltage drops, short-circuit, ... etc. On some
> > > systems
> > > these are a sign of hardware failure and only thing to do is try to
> > > protect the rest of the hardware by shutting down the system.
> > > 
> > > Add shut-down logic which can be used by all subsystems instead of
> > > implementing the shutdown in each subsystem. The logic is stolen
> > > from
> > > thermal_core with difference of using atomic_t instead of a mutex
> > > in
> > > order to allow calls directly from IRQ context.
> > > 
> > > Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
> > > 
> > > diff --git a/kernel/reboot.c b/kernel/reboot.c
> > > index a6ad5eb2fa73..5da8c80a2647 100644
> > > --- a/kernel/reboot.c
> > > +++ b/kernel/reboot.c
> > > @@ -518,6 +519,85 @@ void orderly_reboot(void)
> > >  }
> > >  EXPORT_SYMBOL_GPL(orderly_reboot);
> > >  
> > > +/**
> > > + * hw_failure_emergency_poweroff_func - emergency poweroff work
> > > after a known delay
> > > + * @work: work_struct associated with the emergency poweroff
> > > function
> > > + *
> > > + * This function is called in very critical situations to force
> > > + * a kernel poweroff after a configurable timeout value.
> > > + */
> > > +static void hw_failure_emergency_poweroff_func(struct work_struct
> > > *work)
> > > +{
> > > +	/*
> > > +	 * We have reached here after the emergency shutdown waiting
> > > period has
> > > +	 * expired. This means orderly_poweroff has not been able to
> > > shut off
> > > +	 * the system for some reason.
> > > +	 *
> > > +	 * Try to shut down the system immediately using
> > > kernel_power_off
> > > +	 * if populated
> > > +	 */
> > > +	WARN(1, "Hardware protection timed-out. Trying forced
> > > poweroff\n");
> > > +	kernel_power_off();
> > 
> > WARN() look like an overkill here. It prints many lines that are not
> > much useful in this case. The function is called from well-known
> > context (workqueue worker).
> 
> This was the existing code which I stole from the thermal_core. I kind
> of think that eye-catching WARN is actually a good choice here. Doing
> autonomous power-off without a WARNing does not sound good to me :)
> 
> > Also be aware that "panic_on_warn" commandline option will trigger
> > panic() here.
> 
> Hmm.. If panic() hangs the system that might indeed be a problem. Now
> we are (again) on a territory which I don't know well. I'd appreciate
> any input from thermal folks and Mark. I don't like the idea of making
> extreme things like power-off w/o well visible log-trace. Thus I would
> like to have WARN()-like eye-catcher, even if the call-trace was not
> too varying. It will at least point to this worker. Any better
> suggestions than WARN()?

Heh, it might make sense to create a system wide API for these. I am
sure that WARN() is mis-used this way on many other locations.

There already are two locations that use another eye-catching text.
A common API might help to avoid duplication of the common parts,
see
https://lore.kernel.org/lkml/20210305194206.3165917-2-elver@google.com/

Well, it might be out of scope for this patchset.

Best Regards,
Petr