linux-kernel - Re: [PATCH v2 1/2] ftrace/module: remove ftrace module notifier

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Date:	Thu, 4 Feb 2016 14:27:51 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Jessica Yu <jeyu@...hat.com>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] ftrace/module: remove ftrace module notifier

On Mon 2016-02-01 20:17:35, Jessica Yu wrote:
> Remove the ftrace module notifier in favor of directly calling
> ftrace_module_enable() and ftrace_release_mod() in the module loader.
> Hard-coding the function calls directly in the module loader removes
> dependence on the module notifier call chain and provides better
> visibility and control over what gets called when, which is important
> to kernel utilities such as livepatch.
> 
> Signed-off-by: Jessica Yu <jeyu@...hat.com>
> ---
>  include/linux/ftrace.h |  6 ++++--
>  kernel/module.c        |  4 ++++
>  kernel/trace/ftrace.c  | 36 +-----------------------------------
>  3 files changed, 9 insertions(+), 37 deletions(-)
> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 81de712..c2b340e 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -603,6 +603,7 @@ extern int ftrace_arch_read_dyn_info(char *buf, int size);
>  
>  extern int skip_trace(unsigned long ip);
>  extern void ftrace_module_init(struct module *mod);
> +extern void ftrace_module_enable(struct module *mod);
>  extern void ftrace_release_mod(struct module *mod);
>  
>  extern void ftrace_disable_daemon(void);
> @@ -612,8 +613,9 @@ static inline int skip_trace(unsigned long ip) { return 0; }
>  static inline int ftrace_force_update(void) { return 0; }
>  static inline void ftrace_disable_daemon(void) { }
>  static inline void ftrace_enable_daemon(void) { }
> -static inline void ftrace_release_mod(struct module *mod) {}
> -static inline void ftrace_module_init(struct module *mod) {}
> +static inline void ftrace_module_init(struct module *mod) { }
> +static inline void ftrace_module_enable(struct module *mod) { }
> +static inline void ftrace_release_mod(struct module *mod) { }
>  static inline __init int register_ftrace_command(struct ftrace_func_command *cmd)
>  {
>  	return -EINVAL;
> diff --git a/kernel/module.c b/kernel/module.c
> index 8358f46..b05d466 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -981,6 +981,8 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
>  		mod->exit();
>  	blocking_notifier_call_chain(&module_notify_list,
>  				     MODULE_STATE_GOING, mod);
> +	ftrace_release_mod(mod);
> +
>  	async_synchronize_full();
>  
>  	/* Store the name of the last unloaded module for diagnostic purposes */
> @@ -3295,6 +3297,7 @@ fail:
>  	module_put(mod);
>  	blocking_notifier_call_chain(&module_notify_list,
>  				     MODULE_STATE_GOING, mod);
> +	ftrace_release_mod(mod);
>  	free_module(mod);
>  	wake_up_all(&module_wq);
>  	return ret;
> @@ -3371,6 +3374,7 @@ static int complete_formation(struct module *mod, struct load_info *info)
>  	mod->state = MODULE_STATE_COMING;
>  	mutex_unlock(&module_mutex);
>  
> +	ftrace_module_enable(mod);
>  	blocking_notifier_call_chain(&module_notify_list,
>  				     MODULE_STATE_COMING, mod);
>  	return 0;

Also we need to call ftrace_release_mod() in bug_cleanup:
goto target in load_module(). Otherwise, it will stay
enabled when, e.g. parse_args() fails.

Best Regards,
Petr