linux-kernel - Re: [PATCH v9 02/10] reboot: Add hardware protection power-off

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Message-ID: <2149df3f542d25ce15d049e81d6188bb7198478c.camel@fi.rohmeurope.com>
Date:   Wed, 12 May 2021 12:00:46 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "pmladek@...e.com" <pmladek@...e.com>
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Subject: Re: [PATCH v9 02/10] reboot: Add hardware protection power-off

Hi Petr,

Thanks for the review!

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@...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()?

> 
> > +	/*
> > +	 * Worst of the worst case trigger emergency restart
> > +	 */
> > +	WARN(1,
> > +	     "Hardware protection shutdown failed. Trying emergency
> > restart\n");
> > +	emergency_restart();
> 
> Two consecutive WARN() calls are even less useful. They are eye
> catching but it is hard to find the only useful line with
> the custom message.

I think you are right. One WARN should be enough to point here. This
last one could be just an additional print.

Best Regards
	--Matti Vaittinen