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Subject: Re: [PATCH v9 02/10] reboot: Add hardware protection power-off
From:   Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reply-To: matti.vaittinen@fi.rohmeurope.com
To:     Petr Mladek <pmladek@suse.com>
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On Thu, 2021-05-13 at 10:34 +0200, Petr Mladek wrote:
> 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.

I just had a very brief "chat" with Geert (3 IRC messages, posted
during 4 or 5 days :]) - and Geert pointed me to this:

https://lore.kernel.org/linux-iommu/20210331093104.383705-4-geert+renesas@glider.be/

So, maybe I'll just go with simple pr_emerg() and trust that the
emerg() print should catch attention as such level print probably
should. I'll respin the patch series (probably tomorrow) - let's see
what thermal and regulator folks say :)

Thanks for all the help this far!

Best Regards
	Matti Vaittinen