linux-kernel - Re: Incorrect uses of get_driver()/put

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Date:	Tue, 10 Jan 2012 15:32:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Joerg Roedel <joerg.roedel@....com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Michael Buesch <m@...s.ch>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Incorrect uses of get_driver()/put_driver()

On Tue, 10 Jan 2012, Sebastian Ott wrote:

> [PATCH] cio: remove {get,put}_driver
> 
> Remove useless {get,put}_driver - the caller of the functions
> has to ensure valid driver pointers.
> 
> Signed-off-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> ---
>  drivers/s390/cio/ccwgroup.c |    2 --
>  drivers/s390/cio/device.c   |    8 +-------
>  2 files changed, 1 insertion(+), 9 deletions(-)
> 
> --- a/drivers/s390/cio/ccwgroup.c
> +++ b/drivers/s390/cio/ccwgroup.c
> @@ -580,7 +580,6 @@ void ccwgroup_driver_unregister(struct c
>  	struct device *dev;
>  
>  	/* We don't want ccwgroup devices to live longer than their driver. */
> -	get_driver(&cdriver->driver);
>  	while ((dev = driver_find_device(&cdriver->driver, NULL, NULL,
>  					 __ccwgroup_match_all))) {
>  		struct ccwgroup_device *gdev = to_ccwgroupdev(dev);
> @@ -592,7 +591,6 @@ void ccwgroup_driver_unregister(struct c
>  		mutex_unlock(&gdev->reg_mutex);
>  		put_device(dev);
>  	}
> -	put_driver(&cdriver->driver);
>  	driver_unregister(&cdriver->driver);
>  }
>  EXPORT_SYMBOL(ccwgroup_driver_unregister);
> --- a/drivers/s390/cio/device.c
> +++ b/drivers/s390/cio/device.c
> @@ -1676,15 +1676,9 @@ struct ccw_device *get_ccwdev_by_busid(s
>  				       const char *bus_id)
>  {
>  	struct device *dev;
> -	struct device_driver *drv;
>  
> -	drv = get_driver(&cdrv->driver);
> -	if (!drv)
> -		return NULL;
> -
> -	dev = driver_find_device(drv, NULL, (void *)bus_id,
> +	dev = driver_find_device(&cdrv->driver, NULL, (void *)bus_id,
>  				 __ccwdev_check_busid);
> -	put_driver(drv);
>  
>  	return dev ? to_ccwdev(dev) : NULL;
>  }

Thanks Sebastian and everybody else.  It looks like there's no reason
not to simply remove get_driver() and put_driver(), so I'll do just
that.  This patch can be part of the job -- unless someone else wants
to commit it first.

To avoid possible conflicts, I'll wait until after the merge window 
closes and things stabilize a little before posting any changes.

Alan Stern

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