Re: [PATCH v3] ftrace: Hide a extra entry in stack trace

[Tatsuya S]

On 10/2/24 10:56 PM, Steven Rostedt wrote:

On Wed,  2 Oct 2024 14:13:48 +0900
Tatsuya S <tatsuya.s2...@gmail.com> wrote:

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)

BTW, instead of X'ing it out, can you show what that extra function was.
Just saying "Wrong function name" doesn't give me any idea of what happened.

This is changed each shutdown.
For example, client_init_data, hidpp_driver_init, rfcomm_init.

The same function name was displayed each time if system was not shutdown.

And I added "nokaslr" to the kernel command line and boot, got same result.

=> 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.

Is that the function that was "wrong"?

Unrelated?

-- Steve

Signed-off-by: Tatsuya S <tatsuya.s2...@gmail.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,

thanks