linux-kernel - Re: [PATCH 1/5] [BUGFIX] tracing: Returns -EBUSY when event_enable

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Date:	Thu, 16 May 2013 10:58:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com, Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Tom Zanussi <tom.zanussi@...el.com>
Subject: Re: [PATCH 1/5] [BUGFIX] tracing: Returns -EBUSY when
 event_enable_func fails to get module

On Thu, 2013-05-16 at 20:48 +0900, Masami Hiramatsu wrote:
> Since try_module_get returns false( = 0) when it fails to
> pindown a module, event_enable_func() returns 0 which means
> "succeed". This can cause a kernel panic when the entry
> is removed, because the event is already released.
> 
> This fixes the bug by returning -EBUSY, because the reason
> why it fails is under removing module at that time.
> 

Thanks, this looks to be something that needs to go in right away.

-- Steve

> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> ---
>  kernel/trace/trace_events.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 7a0cf68..27963e2 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -2072,8 +2072,10 @@ event_enable_func(struct ftrace_hash *hash,
>   out_reg:
>  	/* Don't let event modules unload while probe registered */
>  	ret = try_module_get(file->event_call->mod);
> -	if (!ret)
> +	if (!ret) {
> +		ret = -EBUSY;
>  		goto out_free;
> +	}
>  
>  	ret = __ftrace_event_enable_disable(file, 1, 1);
>  	if (ret < 0)


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