From: Jiri Slaby <jslaby@suse.cz>
Date: Thu, 14 Dec 2017 22:54:20 +0100
Subject: x86/stacktrace: make clear the success paths
Patch-mainline: submitted on 2017/12/5
References: bnc#1058115

Make clear which path is for user tasks and for kthreads and idle
tasks. This will allow easier plug-in of ORC unwinder in the next
patches.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/kernel/stacktrace.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -104,16 +104,18 @@ __save_stack_trace_reliable(struct stack
 
 		regs = unwind_get_entry_regs(&state, NULL);
 		if (regs) {
+			/* Success path for user tasks */
+			if (user_mode(regs))
+				goto success;
+
 			/*
 			 * Kernel mode registers on the stack indicate an
 			 * in-kernel interrupt or exception (e.g., preemption
 			 * or a page fault), which can make frame pointers
 			 * unreliable.
 			 */
-			if (!user_mode(regs))
-				return -EINVAL;
 
-			break;
+			return -EINVAL;
 		}
 
 		addr = unwind_get_return_address(&state);
@@ -138,6 +140,11 @@ __save_stack_trace_reliable(struct stack
 		return -EINVAL;
 	}
 
+	/* Success path for non-user tasks, i.e. kthreads and idle tasks */
+	if (!(task->flags & (PF_KTHREAD | PF_IDLE)))
+		return -EINVAL;
+
+success:
 	if (trace->nr_entries < trace->max_entries)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;