linux-kernel - Re: [PATCH] BUG: pinmux: forbid mux_usecount to be set at UINT

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Message-ID: <CACQ1gAjNFgPg+k9MLgGfvWGTYK1mi2nsiQ-LwCu2gdjjL3wkCA@mail.gmail.com>
Date:	Wed, 20 Mar 2013 17:59:46 +0100
From:	Richard Genoud <richard.genoud@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Axel Lin <axel.lin@...ics.com>,
	Stephen Warren <swarren@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] BUG: pinmux: forbid mux_usecount to be set at UINT_MAX

2013/3/20 Stephen Warren <swarren@...dotorg.org>:
> On 03/20/2013 05:31 AM, Richard Genoud wrote:
>> If pin_free is called on a pin already freed, mux_usecount is set to
>> UINT_MAX which is really a bad idea.
>> This will silently ignore a double call to pin_free
>
> Shouldn't we WARN_ON(this case)?
yes indeed, it may be better to issue a big warning because AFAIK
that's not normal.

>
>> diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c
>
>>       if (!gpio_range) {
>> -             desc->mux_usecount--;
>> -             if (desc->mux_usecount)
>> +             if (1 == desc->mux_usecount)
>> +                     desc->mux_usecount = 0;
>> +             else
>>                       return NULL;
>
> What if desc-mux_usecount was 2; this patch prevents the use-count from
> being decremented to 1 in this case. Shouldn't this be:
>
>         if (!gpio_range) {
> +               if (WARN_ON(!desc->mux_usecount))
> +                       return NULL;
>                 desc->mux_usecount--;
>
Well, I'm not very familiar with this code, but can mux_usecount be
higher than 1 ?
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