linux-kernel - [PATCH v3] ftrace: Hide a extra entry in stack trace

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Message-ID: <20241002051347.4239-3-tatsuya.s2862@gmail.com>
Date: Wed,  2 Oct 2024 14:13:48 +0900
From: Tatsuya S <tatsuya.s2862@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Tatsuya S <tatsuya.s2862@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH v3] ftrace: Hide a extra entry in stack trace

A extra entry is shown on stack trace(CONFIG_UNWINDER_ORC=y).

[003] .....   110.171589: vfs_write <-__x64_sys_write
[003] .....   110.171600: <stack trace>
=> XXXXXXXXX (Wrong function name)
=> vfs_write
=> ksys_write
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

To resolve this, increment skip for __ftrace_trace_stack() in
function_stack_trace_call().
The reason why skip is incremented for __ftrace_trace_stack()
is because __ftrace_trace_stack() in stack trace is the only function
that wasn't skipped from anywhere.

Signed-off-by: Tatsuya S <tatsuya.s2862@...il.com>
---
V2 -> V3: Changed the place to increment skip number
V1 -> V2: Fixed redundant code

 kernel/trace/trace_functions.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 3b0cea37e029..27089d8e65d4 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -203,23 +203,21 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
 	ftrace_test_recursion_unlock(bit);
 }
 
-#ifdef CONFIG_UNWINDER_ORC
-/*
- * Skip 2:
- *
- *   function_stack_trace_call()
- *   ftrace_call()
- */
-#define STACK_SKIP 2
-#else
 /*
  * Skip 3:
- *   __trace_stack()
- *   function_stack_trace_call()
- *   ftrace_call()
+ *   Skipped functions if CONFIG_UNWINDER_ORC is defined
+ *
+ *     __ftrace_trace_stack()
+ *     function_stack_trace_call()
+ *     ftrace_call()
+ *
+ *   Otherwise
+ *
+ *     __trace_stack()
+ *     function_stack_trace_call()
+ *     ftrace_call()
  */
 #define STACK_SKIP 3
-#endif
 
 static void
 function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
-- 
2.46.2