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

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Message-ID: <20150120014159.GA3349@kroah.com>
Date:	Tue, 20 Jan 2015 09:41:59 +0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	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 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?

thanks,

greg k-h
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