linux-kernel - Re: [PATCH v5] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

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Date:	Wed, 10 Jun 2015 23:57:44 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	Nicolas Pitre <nico@...aro.org>,
	Tyler Baker <tyler.baker@...aro.org>, linux-sh@...r.kernel.org,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org, Simon Horman <horms@...ge.net.au>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Dave Martin <Dave.Martin@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5] ARM: smp: Only expose /sys/.../cpuX/online if
 hotpluggable

On Tue, Jun 09, 2015 at 12:08:28PM -0700, Stephen Boyd wrote:
> On 04/13/2015 06:42 AM, Russell King - ARM Linux wrote:
> > On Fri, Apr 10, 2015 at 03:33:11PM -0700, Stephen Boyd wrote:
> >> Writes to /sys/.../cpuX/online fail if we determine the platform
> >> doesn't support hotplug for that CPU. Furthermore, if the cpu_die
> >> op isn't specified the system hangs when we try to offline a CPU
> >> and it comes right back online unexpectedly. Let's figure this
> >> stuff out before we make the sysfs nodes so that the online file
> >> doesn't even exist if it isn't (at least sometimes) possible to
> >> hotplug the CPU.
> >>
> >> Add a new 'cpu_can_disable' op and repoint all 'cpu_disable'
> >> implementations at it because all implementers use the op to
> >> indicate if a CPU can be hotplugged or not in a static fashion.
> >> With PSCI we may need to add a 'cpu_disable' op so that the
> >> secure OS can be migrated off the CPU we're trying to hotplug.
> >> In this case, the 'cpu_can_disable' op will indicate that all
> >> CPUs are hotpluggable by returning true, but the 'cpu_disable' op
> >> will make a PSCI migration call and occasionally fail, denying
> >> the hotplug of a CPU. This shouldn't be any worse than x86 where
> >> we may indicate that all CPUs are hotpluggable but occasionally
> >> we can't offline a CPU due to check_irq_vectors_for_cpu_disable()
> >> failing to find a CPU to move vectors to.
> >>
> >> Cc: Mark Rutland <mark.rutland@....com>
> >> Cc: Nicolas Pitre <nico@...aro.org>
> >> Cc: Dave Martin <Dave.Martin@....com>
> >> Acked-by: Simon Horman <horms@...ge.net.au> [shmobile portion]
> >> Tested-by: Simon Horman <horms@...ge.net.au>
> >> Cc: Magnus Damm <magnus.damm@...il.com>
> >> Cc: <linux-sh@...r.kernel.org>
> >> Cc: Tyler Baker <tyler.baker@...aro.org>
> >> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> >> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> > Let's see some more acks for this...
> >
> 
> Nobody else has acked this so far. Shall I put it in the patch tracker
> now? Or is there someone more specific we need an ack from?

The version you've put in the patch tracker is not the version you
posted.  It contains this change:

diff --git a/arch/arm/mach-shmobile/common.h b/arch/arm/mach-shmobile/common.h
index 476092b86c6e..f2c4bf437ea7 100644
--- a/arch/arm/mach-shmobile/common.h
+++ b/arch/arm/mach-shmobile/common.h
@@ -13,7 +13,8 @@ extern void shmobile_smp_boot(void);
 extern void shmobile_smp_sleep(void);
 extern void shmobile_smp_hook(unsigned int cpu, unsigned long fn,
 			      unsigned long arg);
-extern int shmobile_smp_cpu_disable(unsigned int cpu);
+extern bool shmobile_smp_cpu_can_disable(unsigned int cpu);
+extern void shmobile_invalidate_start(void);

which your original patch did not include.  The tree I'm applying to
(-rc1) contains:

extern int shmobile_smp_cpu_disable(unsigned int cpu);
extern void shmobile_invalidate_start(void);

there.  Hence git quite rightfully declines to apply the patch.

Please fix.

Thanks.

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