From mboxrd@z Thu Jan  1 00:00:00 1970
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Date: Thu, 20 Nov 2014 03:53:42 +0000
Subject: Re: [PATCH 1/1] kprobes: Deletion of an unnecessary check before the function call "module_put"
Message-Id: <546D65C6.3030109@hitachi.com>
List-Id: <kernel-janitors.vger.kernel.org>
References: <5307CAA2.8060406@users.sourceforge.net> <alpine.DEB.2.02.1402212321410.2043@localhost6.localdomain6> <530A086E.8010901@users.sourceforge.net> <alpine.DEB.2.02.1402231635510.1985@localhost6.localdomain6> <530A72AA.3000601@users.sourceforge.net> <alpine.DEB.2.02.1402240658210.2090@localhost6.localdomain6> <530B5FB6.6010207@users.sourceforge.net> <alpine.DEB.2.10.1402241710370.2074@hadrien> <530C5E18.1020800@users.sourceforge.net> <alpine.DEB.2.10.1402251014170.2080@hadrien> <530CD2C4.4050903@users.sourceforge.net> <alpine.DEB.2.10.1402251840450.7035@hadrien> <530CF8FF.8080600@users.sourceforge.net> <alpine.DEB.2.02.1402252117150.2047@localhost6.localdomain6> <530DD06F.4090703@users.sourceforge.net> <alpine.DEB.2.02.1402262129250.2221@localhost6.localdomain6> <5317A59D.4@users.sourceforge.net> <546899CF.8020808@users.sourceforge.net> <5469B08E.90104@hitachi.com> <546C41EF.4040502@users.sourceforge.net>
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To: SF Markus Elfring <elfring@users.sourceforge.net>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>, Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>, "David S. Miller" <davem@davemloft.net>, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, Coccinelle <cocci@systeme.lip6.fr>

(2014/11/19 16:08), SF Markus Elfring wrote:
>>> index 3995f54..f1e7d45 100644
>>> --- a/kernel/kprobes.c
>>> +++ b/kernel/kprobes.c
>>> @@ -1527,8 +1527,7 @@ int register_kprobe(struct kprobe *p)
>>>  out:
>>>  	mutex_unlock(&kprobe_mutex);
>>>  
>>> -	if (probed_mod)
>>> -		module_put(probed_mod);
>>> +	module_put(probed_mod);
>>
>> This is OK, but I you request a comment line over there so that
>> code reader can understand it is safe to pass a NULL pointer to
>> module_put().
> 
> Do you want that I replace the shown null pointer check by a short
> comment which repeats an expectation for the affected function call?

No, not "want". IMHO, if try_module_get(mod) is done only when mod!=NULL,
we shouldn't call module_put(mod) when mod=NULL (even if it is possible),
because those get/put method must be used as a pair, for the better
understandings.

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com