linux-kernel - Re: [PATCH] BUG: [RFC] pinctrl: pins are freed 2 times in pinctrl_bind

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Message-ID: <CACQ1gAgjku1c+49H8STASg8jhKwFuLuJ_prhnkcGyknVuZUfpw@mail.gmail.com>
Date:	Thu, 21 Mar 2013 12:31:44 +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: [RFC] pinctrl: pins are freed 2 times in pinctrl_bind_pins

2013/3/20 Stephen Warren <swarren@...dotorg.org>:
> On 03/20/2013 05:31 AM, Richard Genoud wrote:
>> If the function pinctrl_select_state() fails because one pin is already
>> taken elsewhere, pinmux_enable_setting makes all the necessary pin_free
>> calls (and not more than necessary).
>> The problem here is that devm_pinctrl_put() will be called on the pin
>> group, and each pin in this group has already been freed.
>>
>> Example:
>> If a i2c function has already sucessfully taken pins 5 and 6.
>> And now, pinctrl_bind_pins() is called for function PHY (pins 3 4 5 6 7).
>> pinmux_enable_setting() will fail AND call pin_free on necessary pins.
>> But if devm_pinctrl_put() is called, it will call again pin_free on pins
>> 3 4 5 6 7.
>> So, the pins 5 and 6 will be released (and pins 3 4 7 double freed).
>> Which means that even if the i2c function has claim the pins, they will
>> be available for other functions.
>>
>> This patch simply doesn't call devm_pinctrl_put when
>> pinctrl_select_state fails, but I'm not sure it's the right thing to do.
>
> The correct fix here is not to skip the call to devm_pinctrl_put(),
> since that undoes a lot of other things besides the current state selection.
>
> Instead, pinctrl_select_state_locked() needs to be fixed so that:
>
> a)
>
> Change "p->state = state;" to "p->state = NULL;" or similar, to indicate
> that no state is selected. (Please validate if a NULL value in that
> variable will cause problems elsewhere)
>
> b)
>
> Add back the assignment "p->state = state;" at the end of the function,
> if no error occurred.
>
> c)
>
> Fix the list_for_each_entry() call that applies all the settings for the
> new state so that if it fails, it undoes everything that it's applied so
> far. That's the hard part, unless there's a
> list_for_each_entry_before_the_current_one_that_list_for_each_entry_iterated_over_already()
> macro!
ok, I'll look into that.
Thanks for your advices !

PS: with its 90chars long, your macro won't please checkpatch.pl ! :)

Regards,
Richard
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