linux-kernel - Re: [PATCH] tracing/profile: Fix profile_disable vs module

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Date:	Thu, 27 Aug 2009 09:53:59 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

> Peter is correct that he should not need to worry about modules, he 
> doesn't build kernels with them ;-)
> 
> Here's another patch that moves the module ref count administration to the 
> trace events themselves. This should satisfy both you and Peter.
> 

In fact I had this patch in my mind, but I thought Peter insist
on fixing it in tracepoint. So I'm fine with this. :)

> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 1b1f742..3f7c5dc 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -390,6 +390,20 @@ static inline int ftrace_get_offsets_##call(				\
>   *
>   */
>  
> +#ifdef MODULE
> +# define event_trace_up_ref()					\
> +	do {							\
> +		if (!try_module_get(THIS_MODULE)) {		\
> +			atomic_dec(&event_call->profile_count);	\
> +			return -1;				\

Should return -1 or -errno like -ENOENT?

> +		}						\
> +	} while (0)
> +# define event_trace_down_ref() module_put(THIS_MODULE)
> +#else
> +# define event_trace_up_ref() do { } while (0)
> +# define event_trace_down_ref() do { } while (0)
> +#endif
> +		
>  #undef TRACE_EVENT
>  #define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
>  									\
> @@ -399,16 +413,20 @@ static int ftrace_profile_enable_##call(struct ftrace_event_call *event_call) \
>  {									\
>  	int ret = 0;							\
>  									\
> -	if (!atomic_inc_return(&event_call->profile_count))		\
> +	if (!atomic_inc_return(&event_call->profile_count)) {		\
> +		event_trace_up_ref();					\
>  		ret = register_trace_##call(ftrace_profile_##call);	\
> +	}								\
>  									\
>  	return ret;							\
>  }									\
>  									\
>  static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
>  {									\
> -	if (atomic_add_negative(-1, &event_call->profile_count))	\
> +	if (atomic_add_negative(-1, &event_call->profile_count)) {	\
>  		unregister_trace_##call(ftrace_profile_##call);		\
> +		event_trace_down_ref();					\
> +	}								\
>  }
>  
>  #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
> 
> 
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