[PATCH percpu/for-3.18-fixes] s390: fix machine check regression caused by the conversion from __get_cpu_var() to this_cpu_ptr()

[Tejun Heo <tj@kernel.org>]

>From 1bb43105791dae7e9d4d1b1047729b12c5d5c3be Mon Sep 17 00:00:00 2001
From: Sebastian Ott <sebott@linux.vnet.ibm.com>
Date: Fri, 28 Nov 2014 16:03:14 +0100

Commit eb7e7d766326 ("s390: Replace __get_cpu_var uses") broke machine
check handling.

We copy machine check information from per-cpu to a stack variable for
local processing. Next we should zap the per-cpu variable, not the
stack variable.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Christoph Lameter <cl@linux.com>
Fixes: eb7e7d766326 ("s390: Replace __get_cpu_var uses")
Signed-off-by: Tejun Heo <tj@kernel.org>
---
Sorry about the delay.  Was on vacation.

Patch applied to percpu/for-3.18-fixes w/ minor updates to the patch
subject and description.  Will push out to Linus soon.

Thanks.

 arch/s390/kernel/nmi.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/s390/kernel/nmi.c b/arch/s390/kernel/nmi.c
index dd1c24c..3f51cf4 100644
--- a/arch/s390/kernel/nmi.c
+++ b/arch/s390/kernel/nmi.c
@@ -54,12 +54,8 @@ void s390_handle_mcck(void)
 	 */
 	local_irq_save(flags);
 	local_mcck_disable();
-	/*
-	 * Ummm... Does this make sense at all? Copying the percpu struct
-	 * and then zapping it one statement later?
-	 */
-	memcpy(&mcck, this_cpu_ptr(&cpu_mcck), sizeof(mcck));
-	memset(&mcck, 0, sizeof(struct mcck_struct));
+	mcck = *this_cpu_ptr(&cpu_mcck);
+	memset(this_cpu_ptr(&cpu_mcck), 0, sizeof(mcck));
 	clear_cpu_flag(CIF_MCCK_PENDING);
 	local_mcck_enable();
 	local_irq_restore(flags);
-- 
2.1.0