linux-kernel - Re: [PATCH, RFC] uio BKL removal

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Date:	Wed, 27 Aug 2008 10:08:38 +0200
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Jonathan Corbet <corbet@....net>
Cc:	LKML <linux-kernel@...r.kernel.org>, Greg KH <greg@...ah.com>,
	hjk@...utronix.de
Subject: Re: [PATCH, RFC] uio BKL removal

On Tue, Aug 26, 2008 at 05:15:32PM -0600, Jonathan Corbet wrote:
> I had a moment to dedicate to the BKL removal cause, so I went for the
> UIO driver, which seemed simple.  The main thing I found was that there
> was locking around some idr accesses, but not all, so I filled that
> in.  With that in place, removing the BKL from uio_open() seems safe,
> especially since none of the in-tree UIO drivers have open() or
> release() methods.  
> 
> (Incidentally, I don't see how uio_pdrv.c could ever work - who initializes
> uioinfo?)

That has to be done somewhere in your board specific file, e.g. for ARM
boards in arch/arm/mach-xxx/board-something.c - the same place where you
setup your struct platform_device.

> 
> If there's no complaints, I'll feed this into linux-next via the
> bkl-removal tree.

Seems right.

Acked-by: Hans J. Koch <hjk@...utronix.de>

> 
> Thanks,
> 
> jon
> 
> ---
> UIO: BKL removal
> 
> Remove the BKL from the UIO driver, and add complete locking where needed
> to serialize idr accesses.
> 
> Signed-off-by: Jonathan Corbet <corbet@....net>
> 
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index 3a6934b..4f28f4b 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -47,6 +47,9 @@ static struct uio_class {
>  	struct class *class;
>  } *uio_class;
>  
> +/* Protect idr accesses */
> +static DEFINE_MUTEX(minor_lock);
> +
>  /*
>   * attributes
>   */
> @@ -231,7 +234,6 @@ static void uio_dev_del_attributes(struct uio_device *idev)
>  
>  static int uio_get_minor(struct uio_device *idev)
>  {
> -	static DEFINE_MUTEX(minor_lock);
>  	int retval = -ENOMEM;
>  	int id;
>  
> @@ -253,7 +255,9 @@ exit:
>  
>  static void uio_free_minor(struct uio_device *idev)
>  {
> +	mutex_lock(&minor_lock);
>  	idr_remove(&uio_idr, idev->minor);
> +	mutex_unlock(&minor_lock);
>  }
>  
>  /**
> @@ -297,8 +301,9 @@ static int uio_open(struct inode *inode, struct file *filep)
>  	struct uio_listener *listener;
>  	int ret = 0;
>  
> -	lock_kernel();
> +	mutex_lock(&minor_lock);
>  	idev = idr_find(&uio_idr, iminor(inode));
> +	mutex_unlock(&minor_lock);
>  	if (!idev) {
>  		ret = -ENODEV;
>  		goto out;
> @@ -324,18 +329,15 @@ static int uio_open(struct inode *inode, struct file *filep)
>  		if (ret)
>  			goto err_infoopen;
>  	}
> -	unlock_kernel();
>  	return 0;
>  
>  err_infoopen:
> -
>  	kfree(listener);
> -err_alloc_listener:
>  
> +err_alloc_listener:
>  	module_put(idev->owner);
>  
>  out:
> -	unlock_kernel();
>  	return ret;
>  }
>  
--
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