linux-kernel - Re: [PATCH] i2c: drop ancient protection against sysfs refcounting issues

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Message-ID: <54BDFE30.5090303@metafoo.de>
Date:	Tue, 20 Jan 2015 08:05:20 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Wolfram Sang <wsa@...-dreams.de>, linux-mips@...ux-mips.org,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	linux-kernel@...r.kernel.org, Julia Lawall <julia.lawall@...6.fr>,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, Jean Delvare <jdelvare@...e.de>
Subject: Re: [PATCH] i2c: drop ancient protection against sysfs refcounting
 issues

On 01/20/2015 02:41 AM, Greg Kroah-Hartman wrote:
> On Mon, Jan 19, 2015 at 11:04:27PM +0000, Russell King - ARM Linux wrote:
>> On Tue, Jan 20, 2015 at 03:01:42AM +0800, Greg Kroah-Hartman wrote:
>>> On Mon, Jan 19, 2015 at 07:55:56PM +0100, Wolfram Sang wrote:
>>>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
>>>> index 39d25a8cb1ad..15cc5902cf89 100644
>>>> --- a/drivers/i2c/i2c-core.c
>>>> +++ b/drivers/i2c/i2c-core.c
>>>> @@ -41,7 +41,6 @@
>>>>   #include <linux/of_device.h>
>>>>   #include <linux/of_irq.h>
>>>>   #include <linux/clk/clk-conf.h>
>>>> -#include <linux/completion.h>
>>>>   #include <linux/hardirq.h>
>>>>   #include <linux/irqflags.h>
>>>>   #include <linux/rwsem.h>
>>>> @@ -1184,8 +1183,7 @@ EXPORT_SYMBOL_GPL(i2c_new_dummy);
>>>>
>>>>   static void i2c_adapter_dev_release(struct device *dev)
>>>>   {
>>>> -	struct i2c_adapter *adap = to_i2c_adapter(dev);
>>>> -	complete(&adap->dev_released);
>>>> +	/* empty, but the driver core insists we need a release function */
>>>
>>> Yeah, it does, but I hate to see this in "real" code as something is
>>> probably wrong with it if it happens.
>>>
>>> Please move the rest of 'i2c_del_adapter' into the release function
>>> (what was after the wait_for_completion() call), and then all should be
>>> fine.
>>
>> Are you sure about that?  Some drivers do this, eg,
>>
>>          i2c_del_adapter(&drv_data->adapter);
>>          free_irq(drv_data->irq, drv_data);
>>
>> where drv_data was allocated using devm_kzalloc(), and so will be
>> released when the ->remove callback (which calls the above
>> i2c_del_adapter()) returns... freeing the embedded device struct.
>
> But that will fail today if the memory is freed in i2c_del_adapter(), so
> there shouldn't be any change in logic here.
>
> Or am I missing something obvious?

The memory is not freed in i2c_del_adapter().

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