linux-kernel - Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS

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Date:	Tue, 25 Jan 2011 09:11:51 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Vasiliy Kulikov <segooon@...il.com>
CC:	Julia Lawall <julia@...u.dk>,
	Russell King <linux@....linux.org.uk>,
	kernel-janitors@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Andrew Victor <linux@...im.org.za>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS_ERR test

On 01/25/2011 09:05 AM, Vasiliy Kulikov wrote:
> On Mon, Jan 24, 2011 at 21:00 +0100, Julia Lawall wrote:
>> On Tue, 25 Jan 2011, Ryan Mallon wrote:
>>
>>> On 01/25/2011 08:55 AM, Julia Lawall wrote:
>>>> @@ -224,7 +224,7 @@ void __init at91_clock_associate(const char *id, struct device *dev, const char
>>>>  {
>>>>  	struct clk *clk = clk_get(NULL, id);
>>>>  
>>>> -	if (!dev || !clk || !IS_ERR(clk_get(dev, func)))
>>>> +	if (!dev || IS_ERR(clk) || !IS_ERR(clk_get(dev, func)))
>>>>  		return;
>>>
>>> I think we want:
>>>
>>> 	if (!dev || !clk || IS_ERR(clk) || !IS_ERR(clk_get(dev, func)))
>>> 		return;
>>>
>>> Since it is valid to return a NULL clk, and we don't want to try and
>>> dereference it if that is the case.
>>
>> Looking at the given defintion of clk_get, I can't see how that could 
>> happen:
> 
> clk_get() is defined per-architecture, sometimes it is NULL only.

Julia is correct. Some architectures can return NULL from clk_get, but I
didn't check the at91 before posting :-/. If we can't return NULL from
clk_get then we shouldn't bother checking for it. I do think we should
drop the !IS_ERR(clk_get(dev, func)) check though.

~Ryan

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