From: Vasily Gorbik <gor@linux.ibm.com>
Date: Fri, 22 Nov 2019 12:19:16 +0100
Subject: s390: disable preemption when switching to nodat stack with
 CALL_ON_STACK
Git-commit: 7f28dad395243c5026d649136823bbc40029a828
Patch-mainline: v5.5-rc1
References: jsc#SLE-11178

Make sure preemption is disabled when temporary switching to nodat
stack with CALL_ON_STACK helper, because nodat stack is per cpu.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 arch/s390/kernel/machine_kexec.c |    2 ++
 arch/s390/mm/maccess.c           |   12 +++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

--- a/arch/s390/kernel/machine_kexec.c
+++ b/arch/s390/kernel/machine_kexec.c
@@ -162,7 +162,9 @@ static int kdump_csum_valid(struct kimag
 #ifdef CONFIG_CRASH_DUMP
 	int rc;
 
+	preempt_disable();
 	rc = CALL_ON_STACK(do_start_kdump, S390_lowcore.nodat_stack, 1, image);
+	preempt_enable();
 	return rc ? 0 : -EINVAL;
 #else
 	return -EINVAL;
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -114,9 +114,15 @@ static unsigned long _memcpy_real(unsign
  */
 int memcpy_real(void *dest, void *src, size_t count)
 {
-	if (S390_lowcore.nodat_stack != 0)
-		return CALL_ON_STACK(_memcpy_real, S390_lowcore.nodat_stack,
-				     3, dest, src, count);
+	int rc;
+
+	if (S390_lowcore.nodat_stack != 0) {
+		preempt_disable();
+		rc = CALL_ON_STACK(_memcpy_real, S390_lowcore.nodat_stack, 3,
+				   dest, src, count);
+		preempt_enable();
+		return rc;
+	}
 	/*
 	 * This is a really early memcpy_real call, the stacks are
 	 * not set up yet. Just call _memcpy_real on the early boot