x86/stacktrace: Remove the pointless ULONG_MAX marker

Terminating the last trace entry with ULONG_MAX is a completely pointless
exercise and none of the consumers can rely on it because it's
inconsistently implemented across architectures. In fact quite some of the
callers remove the entry and adjust stack_trace.nr_entries afterwards.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexander Potapenko <glider@google.com>
Link: https://lkml.kernel.org/r/20190410103643.750954603@linutronix.de

arch/x86/kernel/stacktrace.c

@@ -46,9 +46,6 @@ static void noinline __save_stack_trace(struct stack_trace *trace,
 		if (!addr || save_stack_address(trace, addr, nosched))
 			break;
 	}
-
-	if (trace->nr_entries < trace->max_entries)
-		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
 
 /*
@@ -97,7 +94,7 @@ __save_stack_trace_reliable(struct stack_trace *trace,
 		if (regs) {
 			/* Success path for user tasks */
 			if (user_mode(regs))
-				goto success;
+				return 0;
 
 			/*
 			 * Kernel mode registers on the stack indicate an
@@ -132,10 +129,6 @@ __save_stack_trace_reliable(struct stack_trace *trace,
 	if (!(task->flags & (PF_KTHREAD | PF_IDLE)))
 		return -EINVAL;
 
-success:
-	if (trace->nr_entries < trace->max_entries)
-		trace->entries[trace->nr_entries++] = ULONG_MAX;
-
 	return 0;
 }
 
@@ -221,9 +214,6 @@ void save_stack_trace_user(struct stack_trace *trace)
 	/*
 	 * Trace user stack if we are not a kernel thread
 	 */
-	if (current->mm) {
+	if (current->mm)
 		__save_stack_trace_user(trace);
-	}
-	if (trace->nr_entries < trace->max_entries)
-		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }