From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out-231.synserver.de (smtp-out-231.synserver.de [212.40.185.231]) by lists.ozlabs.org (Postfix) with ESMTP id C1B321A0C35 for ; Tue, 20 Jan 2015 18:25:39 +1100 (AEDT) Message-ID: <54BE0364.7060404@metafoo.de> Date: Tue, 20 Jan 2015 08:27:32 +0100 From: Lars-Peter Clausen MIME-Version: 1.0 To: Greg Kroah-Hartman Subject: Re: [PATCH] i2c: drop ancient protection against sysfs refcounting issues References: <1421693756-12917-1-git-send-email-wsa@the-dreams.de> <20150119190142.GA9451@kroah.com> <20150119230427.GH26493@n2100.arm.linux.org.uk> <20150120014159.GA3349@kroah.com> <54BDFE30.5090303@metafoo.de> <20150120071256.GA18983@kroah.com> In-Reply-To: <20150120071256.GA18983@kroah.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-mips@linux-mips.org, Russell King - ARM Linux , Wolfram Sang , Pantelis Antoniou , linux-kernel@vger.kernel.org, Julia Lawall , Jean Delvare , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 01/20/2015 08:12 AM, Greg Kroah-Hartman wrote: > On Tue, Jan 20, 2015 at 08:05:20AM +0100, Lars-Peter Clausen wrote: >> 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 >>>>>> #include >>>>>> #include >>>>>> -#include >>>>>> #include >>>>>> #include >>>>>> #include >>>>>> @@ -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(). > > Right, and I'm not saying it should be, just move the existing logic > into the release callback, and the code flow should be the same and we > don't end up with an "empty" release callback. But the code flow often is. i2c_del_adapter(&drvdata->adap); kfree(drvdata); That wont work anymore if i2c_del_adapter() returns before the last reference has been dropped. This needs to be restructured so that the adapter memory can be freed by the release callback.