[PATCH] s390/unwind: use current_frame_address() to unwind current task

[Vasily Gorbik <gor@linux.ibm.com>]

current_stack_pointer() simply returns current value of %r15. If
current_stack_pointer() caller allocates stack (which is the case in
unwind code) %r15 points to a stack frame allocated for callees, meaning
current_stack_pointer() caller (e.g. stack_trace_save) will end up in
the stacktrace. This is not expected by stack_trace_save*() callers and
causes problems.

current_frame_address() on the other hand returns function stack frame
address, which matches %r15 upon function invocation. Using it in
get_stack_pointer() makes it more aligned with x86 implementation
(according to BACKTRACE_SELF_TEST output) and meets stack_trace_save*()
caller's expectations, notably KCSAN.

Also make sure unwind_start is always inlined.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---
 arch/s390/include/asm/stacktrace.h | 20 ++++++++++----------
 arch/s390/include/asm/unwind.h     |  8 ++++----
 2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
index 3d8a4b94c620..22c41d7fd95c 100644
--- a/arch/s390/include/asm/stacktrace.h
+++ b/arch/s390/include/asm/stacktrace.h
@@ -34,16 +34,6 @@ static inline bool on_stack(struct stack_info *info,
 	return addr >= info->begin && addr + len <= info->end;
 }
 
-static __always_inline unsigned long get_stack_pointer(struct task_struct *task,
-						       struct pt_regs *regs)
-{
-	if (regs)
-		return (unsigned long) kernel_stack_pointer(regs);
-	if (task == current)
-		return current_stack_pointer();
-	return (unsigned long) task->thread.ksp;
-}
-
 /*
  * Stack layout of a C stack frame.
  */
@@ -74,6 +64,16 @@ struct stack_frame {
 	((unsigned long)__builtin_frame_address(0) -			\
 	 offsetof(struct stack_frame, back_chain))
 
+static __always_inline unsigned long get_stack_pointer(struct task_struct *task,
+						       struct pt_regs *regs)
+{
+	if (regs)
+		return (unsigned long) kernel_stack_pointer(regs);
+	if (task == current)
+		return current_frame_address();
+	return (unsigned long) task->thread.ksp;
+}
+
 /*
  * To keep this simple mark register 2-6 as being changed (volatile)
  * by the called function, even though register 6 is saved/nonvolatile.
diff --git a/arch/s390/include/asm/unwind.h b/arch/s390/include/asm/unwind.h
index de9006b0cfeb..5ebf534ef753 100644
--- a/arch/s390/include/asm/unwind.h
+++ b/arch/s390/include/asm/unwind.h
@@ -55,10 +55,10 @@ static inline bool unwind_error(struct unwind_state *state)
 	return state->error;
 }
 
-static inline void unwind_start(struct unwind_state *state,
-				struct task_struct *task,
-				struct pt_regs *regs,
-				unsigned long first_frame)
+static __always_inline void unwind_start(struct unwind_state *state,
+					 struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long first_frame)
 {
 	task = task ?: current;
 	first_frame = first_frame ?: get_stack_pointer(task, regs);
-- 
2.25.4