tracing: Fix user stack trace "??" output

commit 6d54ceb539aacc3df65c89500e8b045924f3ef81 upstream.

Commit c5c27a0a5838 ("x86/stacktrace: Remove the pointless ULONG_MAX
marker") removes ULONG_MAX marker from user stack trace entries but
trace_user_stack_print() still uses the marker and it outputs unnecessary
"??".

For example:

            less-1911  [001] d..2    34.758944: <user stack trace>
   =>  <00007f16f2295910>
   => ??
   => ??
   => ??
   => ??
   => ??
   => ??
   => ??

The user stack trace code zeroes the storage before saving the stack, so if
the trace is shorter than the maximum number of entries it can terminate
the print loop if a zero entry is detected.

Link: http://lkml.kernel.org/r/20190630085438.25545-1-devel@etsukata.com

Cc: stable@vger.kernel.org
Fixes: 4285f2fcef80 ("tracing: Remove the ULONG_MAX stack trace hackery")
Signed-off-by: Eiichi Tsukata <devel@etsukata.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 1 insertions, 8 deletions

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index ba751f993c3b6..cab4a5398f1d4 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1109,17 +1109,10 @@ static enum print_line_t trace_user_stack_print(struct trace_iterator *iter,
 	for (i = 0; i < FTRACE_STACK_ENTRIES; i++) {
 		unsigned long ip = field->caller[i];
 
-		if (ip == ULONG_MAX || trace_seq_has_overflowed(s))
+		if (!ip || trace_seq_has_overflowed(s))
 			break;
 
 		trace_seq_puts(s, " => ");
-
-		if (!ip) {
-			trace_seq_puts(s, "??");
-			trace_seq_putc(s, '\n');
-			continue;
-		}
-
 		seq_print_user_ip(s, mm, ip, flags);
 		trace_seq_putc(s, '\n');
 	}