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.s2862@xxxxxxxxx> 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.s2862@xxxxxxxxx>
> > ---
> > 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