linux-kernel - Re: ftrace/perf

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Message-ID: <4C7EFBE6.3040408@cn.fujitsu.com>
Date:	Thu, 02 Sep 2010 09:20:38 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Avi Kivity <avi@...hat.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

>> 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).

The failure should be a rare case, I don't think this has to be backported?

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

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