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

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Date:	Wed, 20 Mar 2013 10:14:00 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Richard Genoud <richard.genoud@...il.com>
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

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)?

> 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--;

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