linux-kernel - Re: [PATCH v2] reboot: Backup orderly

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Message-ID: <20160115101312.GA23349@gmail.com>
Date:	Fri, 15 Jan 2016 11:13:12 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Keerthy <a0393675@...com>, nm@...com, grygorii.strashko@...com,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-pm@...r.kernel.org, peterz@...radead.org,
	Keerthy <j-keerthy@...com>, linux-kernel@...r.kernel.org,
	josh@...htriplett.org, edubezval@...il.com, joel@....id.au,
	mpe@...erman.id.au, akpm@...ux-foundation.org,
	linux-omap@...r.kernel.org, dyoung@...hat.com,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] reboot: Backup orderly_poweroff

* Russell King - ARM Linux <linux@....linux.org.uk> wrote:

> On Thu, Jan 14, 2016 at 12:23:54PM +0100, Ingo Molnar wrote:
> > * Keerthy <a0393675@...com> wrote:
> > > I tried to simulate the issue.
> > > 
> > > In the probe function of drivers/thermal/ti-soc-thermal/ti-bandgap.c
> > > ti_bandgap_probe i call
> > > 
> > > orderly_poweroff(true);
> > > 
> > > This is while driver probes are still on going. I observe that
> > > ret = run_cmd(poweroff_cmd);
> > > 
> > > ret is a non-zero value and we enter the if condition:
> > > 
> > > Even after the
> > > 
> > > emergency_sync();
> > > kernel_power_off();
> > > 
> > > calls
> > > 
> > > the console remained active in weird state.
> > 
> > Now _that_ is clearly an architecture bug that should not be papered over ...
> 
> No, it's not an architecture bug - it's a platform bug. [...]

It's an 'architecture bug' in Linux kernel speak: all stuff that is traditionally 
under arch/*. The 'arch' in that directory name derives from 'architecture'.

kernel_power_off() is a traditionally architecture level (not core kernel level 
and not driver level) code.

> [...] The ARM architecture has no standard way to control CPU reset or system 
> power, all that is up to the platform.

... and platform code is typically part of arch/ as well.

FYI, you are making an unnecessarily obtuse argument by insisting on the 
architecture != platform triviality and you also injected an uncalled for 
patronizing tone into this discussion by pretending that I don't know that 
distinction. It's sad.

> > If kernel_power_off() is called then the system should power off. No ifs and 
> > whens.
> 
> There definitely are ifs and whens.  Only if the platform has support, and when 
> that support works.

And that is precisely what I meant: in a correctly working kernel, with correctly 
working hardware, in a correctly working universe, the core kernel expects 
kernel_power_off() to never 'fail'.

As the name suggests.

Yes, bugs in user-space, kernel-space, hardware and designed buggy hardware might 
prevent a reboot - as usual.

I.e. I NAK this patch from a core kernel perspective, we don't add such 
workarounds without a lot more information about why it's the right thing to do.

Thanks,

	Ingo