From: Jiri Slaby <jslaby@suse.cz>
Date: Fri, 18 May 2018 08:47:10 +0200
Subject: x86/stacktrace: Clarify the reliable success paths
Git-commit: 441ccc3580f45340715fd8f5c4db795b06326404
Patch-mainline: v4.19-rc1
References: bnc#1058115

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

Note that we added a check for unwind error to the top of the loop, so
that an error is returned also for user tasks (the 'goto success' would
skip the check after the loop otherwise).

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/lkml/20180518064713.26440-3-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/stacktrace.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -89,21 +89,24 @@ __save_stack_trace_reliable(struct stack
 	struct pt_regs *regs;
 	unsigned long addr;
 
-	for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state);
+	for (unwind_start(&state, task, NULL, NULL);
+	     !unwind_done(&state) && !unwind_error(&state);
 	     unwind_next_frame(&state)) {
 
 		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);
@@ -124,6 +127,11 @@ __save_stack_trace_reliable(struct stack
 	if (unwind_error(&state))
 		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;