From: Ilya Leoshkevich <iii@linux.ibm.com>
Date: Wed, 2 Oct 2019 12:56:27 +0200
Subject: s390/unwind: fix get_stack_pointer(NULL, NULL)
Git-commit: ea3f6dcfa71afb51753ad3729c29570f90d6abbc
Patch-mainline: v5.5-rc1
References: jsc#SLE-11178

unwind_for_each_frame(NULL, NULL, 0) does not return any valid frames.

The reason is that get_stack_pointer, unlike get_stack_info and
show_stack, does not handle NULL argument.

Fix by making get_stack_pointer treat NULL as current, like
get_stack_info and show_stack do.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Tested-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 arch/s390/include/asm/stacktrace.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
index 0ae4bbf7779c..fee40212af11 100644
--- a/arch/s390/include/asm/stacktrace.h
+++ b/arch/s390/include/asm/stacktrace.h
@@ -38,7 +38,7 @@ static inline unsigned long get_stack_pointer(struct task_struct *task,
 {
 	if (regs)
 		return (unsigned long) kernel_stack_pointer(regs);
-	if (task == current)
+	if (!task || task == current)
 		return current_stack_pointer();
 	return (unsigned long) task->thread.ksp;
 }