linux-kernel - Re: ftrace/perf

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Date:	Wed, 1 Sep 2010 14:15:20 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Avi Kivity <avi@...hat.com>, Li Zefan <lizf@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	kvm-devel <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: ftrace/perf_event leak

On Wed, Sep 01, 2010 at 01:02:57PM +0200, Peter Zijlstra wrote:
> On Wed, 2010-09-01 at 13:38 +0300, Avi Kivity wrote:
> > On 09/01/2010 12:38 PM, Li Zefan wrote:
> > >
> > > Then try this:
> > 
> > Tested-by: Avi Kivity <avi@...hat.com>
> > 
> 
> Thanks, queued as:
> 
> ---
> Subject: perf, trace: Fix module leak
> From: Li Zefan <lizf@...fujitsu.com>
> Date: Wed Sep 01 12:58:43 CEST 2010
> 
> Commit 1c024eca (perf, trace: Optimize tracepoints by using
> per-tracepoint-per-cpu hlist to track events) caused a module refcount
> leak.
> 
> Tested-by: Avi Kivity <avi@...hat.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> LKML-Reference: <4C7E1F12.8030304@...fujitsu.com>
> ---
>  kernel/trace/trace_event_perf.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6/kernel/trace/trace_event_perf.c
> ===================================================================
> --- linux-2.6.orig/kernel/trace/trace_event_perf.c
> +++ linux-2.6/kernel/trace/trace_event_perf.c
> @@ -91,6 +91,8 @@ int perf_trace_init(struct perf_event *p
>  		    tp_event->class && tp_event->class->reg &&
>  		    try_module_get(tp_event->mod)) {
>  			ret = perf_trace_event_init(tp_event, p_event);
> +			if (ret)
> +				module_put(tp_event->mod);
>  			break;
>  		}
>  	}
> @@ -147,6 +149,7 @@ void perf_trace_destroy(struct perf_even
>  		}
>  	}
>  out:
> +	module_put(tp_event->mod);
>  	mutex_unlock(&event_mutex);
>  }
>  
> 



Thanks for fixing this.

However, can we split this in two patches to ease the backport?

The lack of a module_put() after perf_trace_init() failure is there for a while
(the backport needs to start in 2.6.32).

But the lack of a module_put in the destroy path needs a .35 backport only.

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