[ 3.8.y.z extended stable ] Patch "powerpc/pseries: Always enable CONFIG_HOTPLUG_CPU on PSERIES SMP" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    powerpc/pseries: Always enable CONFIG_HOTPLUG_CPU on PSERIES SMP

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From ea360ea523857449b5f183f275dc366484ba4eeb Mon Sep 17 00:00:00 2001
From: "Srivatsa S. Bhat" <srivatsa.bhat at linux.vnet.ibm.com>
Date: Tue, 21 May 2013 09:32:48 +0000
Subject: powerpc/pseries: Always enable CONFIG_HOTPLUG_CPU on PSERIES SMP
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit f274ef8747d3be649bba8708696fb31cb00fa75a upstream.

Adam Lackorzynski reported the following build failure on
!CONFIG_HOTPLUG_CPU configuration:

  CC      arch/powerpc/kernel/rtas.o
arch/powerpc/kernel/rtas.c: In function ‘rtas_cpu_state_change_mask’:
arch/powerpc/kernel/rtas.c:843:4: error: implicit declaration of function ‘cpu_down’ [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors
make[1]: *** [arch/powerpc/kernel/rtas.o] Error 1
make: *** [arch/powerpc/kernel] Error 2

The build fails because cpu_down() is defined only under CONFIG_HOTPLUG_CPU.

Looking further, the mobility code in pseries is one of the call-sites which
uses rtas_ibm_suspend_me(), which in turn calls rtas_cpu_state_change_mask().
And the mobility code is unconditionally compiled-in (it does not fall under
any Kconfig option). And commit 120496ac (powerpc: Bring all threads online
prior to migration/hibernation) which introduced this build regression is
critical for the proper functioning of the migration code. So it appears
that the only solution to this problem is to enable CONFIG_HOTPLUG_CPU if
SMP is enabled on PPC_PSERIES platforms. So make that change in the Kconfig.

Reported-by: Adam Lackorzynski <adam at os.inf.tu-dresden.de>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/powerpc/platforms/pseries/Kconfig | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index 837cf49..c7a8425 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -17,6 +17,8 @@ config PPC_PSERIES
 	select PPC_NATIVE
 	select PPC_PCI_CHOICE if EXPERT
 	select ZLIB_DEFLATE
+	select HOTPLUG if SMP
+	select HOTPLUG_CPU if SMP
 	default y

 config PPC_SPLPAR
--
1.8.1.2