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Re: [PATCH v2 1/4] clk: add common __clk_get(), __clk_put() implement

To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: [PATCH v2 1/4] clk: add common __clk_get(), __clk_put() implementations
From: Sylwester Nawrocki <s.nawrocki@samsung.com>
Date: Fri, 23 Aug 2013 16:41:29 +0200
Cc: linux-arm-kernel@lists.infradead.org, mturquette@linaro.org, jiada_wang@mentor.com, robherring2@gmail.com, grant.likely@linaro.org, broonie@kernel.org, vapier@gentoo.org, ralf@linux-mips.org, kyungmin.park@samsung.com, shawn.guo@linaro.org, sebastian.hesselbarth@gmail.com, LW@KARO-electronics.de, t.figa@samsung.com, g.liakhovetski@gmx.de, laurent.pinchart@ideasonboard.com, linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, linux-mips@linux-mips.org, linux-sh@vger.kernel.org
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On 08/20/2013 10:30 PM, Russell King - ARM Linux wrote:
> On Tue, Aug 20, 2013 at 07:34:20PM +0200, Sylwester Nawrocki wrote:
>> +int __clk_get(struct clk *clk)
>> +{
>> +    if (WARN_ON((!clk)))
>> +            return 0;
> 
> This changes the behaviour of clk_get()

My bad, will remove that.

>> +
>> +    if (!try_module_get(clk->owner))
>> +            return 0;
> 
> If you want this to be safe against NULL pointers, just do this:
> 
>       if (clk && !try_module_get(clk->owner))
>               return 0;

Ok, that should work too.

>> +
>> +    return 1;
>> +}
>> +EXPORT_SYMBOL(__clk_get);
>> +
>> +void __clk_put(struct clk *clk)
>> +{
>> +    if (!clk || IS_ERR(clk))
>> +            return;
>> +
>> +    module_put(clk->owner);
> 
> Calling clk_put() with an error-pointer should be a Bad Thing and something
> that shouldn't be encouraged, so trapping it is probably unwise.  So, just
> do here:
> 
>       if (clk)
>               module_put(clk->owner);
> 
> If we do have some callers of this with ERR pointers, then we could add:
> 
>       if (WARN_ON_ONCE(IS_ERR(clk)))
>               return;
> 
> and remove it after a full kernel cycle or so.

I wouldn't be surprised to see some callers with ERR pointers, since
clk_put() has been mostly a no op. I'm inclined to leave such a check
temporarily, let's see if it catches any issues.

Thanks for review of the other patches.

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