linux-kernel - Re: [PATCH] ARM: machine_power

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Message-ID: <20140326105940.GX7528@n2100.arm.linux.org.uk>
Date:	Wed, 26 Mar 2014 10:59:40 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	Sebastian Capella <sebastian.capella@...aro.org>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linaro-kernel@...ts.linaro.org, Len Brown <len.brown@...el.com>,
	Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: machine_power_off should not return

On Wed, Mar 26, 2014 at 07:12:27AM -0300, Ezequiel Garcia wrote:
> On Mar 26, Russell King - ARM Linux wrote:
> > On Tue, Mar 25, 2014 at 07:45:55PM -0300, Ezequiel Garcia wrote:
> > > 
> > > Without this patch we got the heartbeat's reboot_notifier called twice while
> > > testing the recent hibernation patches, which was unexpected and produced a
> > > kernel panic: https://lkml.org/lkml/2014/3/19/363
> > 
> > I don't see why we should make this change.  kernel/reboot.c handles
> > this function returning, so other places should do too.
> > 
> > Even on x86, this function can return:
> > 
> [..]
> > 
> > Therefore, I'd say... it's a bug in the hibernation code - or we probably
> > have many buggy architectures.  I'd suggest fixing the hibernation code
> > rather than stuffing some workaround like an endless loop into every
> > architecture.
> > 
> 
> Which is exactly what Sebastian did first:
> 
> https://lkml.org/lkml/2014/3/20/605
> 
> But Pavel asked to fix ARM's machine_power_off instead.
> 
> Also, looking at the other architectures, it seems this API is not well
> defined: some of them have an infinite loop, some don't. So it's hard to
> say the function is supposed to return or not.

I'm going by x86 (which I regard as definitive) and the generic power-off
kernel code (which I've looked at all the way back to 2.6.12-rc2).

The hibernation code path should really be fixed - the paths in
kernel/reboot.c have coped for 9+ with all of these platform hooks
returning, and it's only the silly switch() in the hibernation code
that doesn't use a "default" case to handle the kernel_halt() case
which is the real cause of the problem.

As you've found, calling kernel_power_off() followed by kernel_halt()
leads to bugs in drivers: this is not an architecture thing, it's partly
a hibernation code failure for doing that, and partly a driver bug for
trying to unregister something that it's already unregistered.

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