linux-kernel - Re: [PATCH 3/9] ftrace: Fix shutdown to disable calls properly

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Date:	Mon, 28 Nov 2011 14:18:48 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	fweisbec@...il.com, mingo@...hat.com, paulus@...ba.org,
	acme@...stprotocols.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/9] ftrace: Fix shutdown to disable calls properly

On Sun, 2011-11-27 at 19:04 +0100, Jiri Olsa wrote:
> Each ftrace_startup call increases the call record's flag,
> so we need allways to decrease it when shutting down the
> ftrace_ops.

No, that's not how this works. I probably should comment this code
better, because it caused me to reread it too ;)

> 
> Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> ---
>  kernel/trace/ftrace.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index c6d0293..0ca0c0d 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1744,8 +1744,7 @@ static void ftrace_shutdown(struct ftrace_ops *ops, int command)
>  	if (ops != &global_ops || !global_start_up)
>  		ops->flags &= ~FTRACE_OPS_FL_ENABLED;
>  
> -	if (!ftrace_start_up)
> -		command |= FTRACE_DISABLE_CALLS;
> +	command |= FTRACE_DISABLE_CALLS;

FTRACE_DISABLE_CALLS will disable *all* functions for all tracers. If
you are tracing with ftrace and perf, and one calls this with
FTRACE_DISABLE_CALLS then both will no long be tracing anything.

When you call unregister_ftrace_function() it will disable the functions
that you have enabled by the ops.

Nacked-by: Steven Rostedt <rostedt@...dmis.org.

-- Steve


>  
>  	if (saved_ftrace_func != ftrace_trace_function) {
>  		saved_ftrace_func = ftrace_trace_function;


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