Re: [PATCH] ARM: machine_power_off should not return

Russell King - ARM Linux
2014-03-26T11:00:05Z

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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