linux-kernel - [PATCH] tracing: Fix user stack trace "??" output

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Message-Id: <20190630085438.25545-1-devel@etsukata.com>
Date:   Sun, 30 Jun 2019 17:54:38 +0900
From:   Eiichi Tsukata <devel@...ukata.com>
To:     rostedt@...dmis.org, tglx@...utronix.de, peterz@...radead.org,
        mingo@...hat.com, linux-kernel@...r.kernel.org
Cc:     Eiichi Tsukata <devel@...ukata.com>
Subject: [PATCH] tracing: Fix user stack trace "??" output

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.

Fixes: 4285f2fcef80 ("tracing: Remove the ULONG_MAX stack trace hackery")
Signed-off-by: Eiichi Tsukata <devel@...ukata.com>
---
 kernel/trace/trace_output.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index ba751f993c3b..cab4a5398f1d 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');
 	}
-- 
2.21.0