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

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Message-ID: <5298f02a-406b-4f1e-bc1d-f34217eb20bc@gmail.com>
Date: Thu, 26 Sep 2024 14:43:56 +0900
From: ts <tatsuya.s2862@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: Hide a extra entry in stack trace

On 9/26/24 2:05 PM, Steven Rostedt wrote:

> On Mon, 23 Sep 2024 12:59:15 +0900
> Tatsuya S <tatsuya.s2862@...il.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)
>>   => vfs_write
>>   => __x64_sys_write
>>   => do_syscall_64
>>   => entry_SYSCALL_64_after_hwframe
>>
>> To resolve this, increment skip in __ftrace_trace_stack().
>> The reason why skip is incremented in __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>
>> ---
>>   kernel/trace/trace.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index c3b2c7dfadef..e0d98621ff23 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -2919,6 +2919,8 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer,
>>   #ifndef CONFIG_UNWINDER_ORC
>>   	if (!regs)
>>   		skip++;
>> +#else
>> +	skip++;
>>   #endif
> The above #ifdef block should be removed and replaced with;
>
>
> 	if (IS_ENABLED(CONFIG_UNWINDER_ORC) || !regs)
> 		skip++;
>
>>   
>>   	preempt_disable_notrace();
> -- Steve

  I will submit a new patch to fix it.

Thanks.