linux-kernel - Re: [PATCH resend v2] ftrace: nuke clear_ftrace

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Date:   Wed, 9 May 2018 08:56:43 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Yisheng Xie <xieyisheng1@...wei.com>
Cc:     <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH resend v2] ftrace: nuke clear_ftrace_function

On Wed, 9 May 2018 17:33:56 +0800
Yisheng Xie <xieyisheng1@...wei.com> wrote:

> clear_ftrace_function is not used outside of ftrace.c and is not help to
> use a function, so nuke it per Steve's suggestion.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
> ---
> v2:
>  - nuke clear_ftrace_function instead of use it - per Steve
> 
> v1:
>  - https://lkml.org/lkml/2018/1/29/944
> 
>  include/linux/ftrace.h |  2 --
>  kernel/trace/ftrace.c  | 13 +------------
>  2 files changed, 1 insertion(+), 14 deletions(-)
> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 9c3c9a3..15518b5 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -223,7 +223,6 @@ enum ftrace_tracing_type_t {
>   */
>  int register_ftrace_function(struct ftrace_ops *ops);
>  int unregister_ftrace_function(struct ftrace_ops *ops);
> -void clear_ftrace_function(void);
>  
>  extern void ftrace_stub(unsigned long a0, unsigned long a1,
>  			struct ftrace_ops *op, struct pt_regs *regs);
> @@ -239,7 +238,6 @@ static inline int ftrace_nr_registered_ops(void)
>  {
>  	return 0;
>  }
> -static inline void clear_ftrace_function(void) { }
>  static inline void ftrace_kill(void) { }
>  static inline void ftrace_free_init_mem(void) { }
>  static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 8d83bcf..d4984f4 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -192,17 +192,6 @@ static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip,
>  	op->saved_func(ip, parent_ip, op, regs);
>  }
>  
> -/**
> - * clear_ftrace_function - reset the ftrace function
> - *
> - * This NULLs the ftrace function and in essence stops
> - * tracing.  There may be lag
> - */

I agree that the function should be removed, but the comment is still
relevant.

> -void clear_ftrace_function(void)
> -{
> -	ftrace_trace_function = ftrace_stub;
> -}
> -
>  static void ftrace_sync(struct work_struct *work)
>  {
>  	/*
> @@ -6689,7 +6678,7 @@ void ftrace_kill(void)
>  {
>  	ftrace_disabled = 1;
>  	ftrace_enabled = 0;
> -	clear_ftrace_function();

	/* This will stop tracing, but there may be a lag */

-- Steve

> +	ftrace_trace_function = ftrace_stub;
>  }
>  
>  /**