linux-kernel - Re: [PATCH 1/1] kprobes: Deletion of an unnecessary check before the function call "module

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Date:	Thu, 20 Nov 2014 12:53:42 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	Coccinelle <cocci@...teme.lip6.fr>
Subject: Re: [PATCH 1/1] kprobes: Deletion of an unnecessary check before
 the function call "module_put"

(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@...achi.com


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