linux-kernel - Re: [PATCH 2/3 v2] fb: udlfb: fix hang at disconnect

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Message-Id: <20130128162238.7fba92fe.akpm@linux-foundation.org>
Date:	Mon, 28 Jan 2013 16:22:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alexander Holler <holler@...oftware.de>
Cc:	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Bernie Thompson <bernie@...gable.com>,
	Steve Glendinning <steve.glendinning@...well.net>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH 2/3 v2] fb: udlfb: fix hang at disconnect

On Fri, 25 Jan 2013 19:49:27 +0100
Alexander Holler <holler@...oftware.de> wrote:

> When a device was disconnected the driver may hang at waiting for urbs it never
> will get. Fix this by using a timeout while waiting for the used semaphore.
> 
> There is still a memory leak if a timeout happens, but at least the driver
> now continues his disconnect routine.
> 
> ...
>
> --- a/drivers/video/udlfb.c
> +++ b/drivers/video/udlfb.c
> @@ -1832,8 +1832,9 @@ static void dlfb_free_urb_list(struct dlfb_data *dev)
>  	/* keep waiting and freeing, until we've got 'em all */
>  	while (count--) {
>  
> -		/* Getting interrupted means a leak, but ok at disconnect */
> -		ret = down_interruptible(&dev->urbs.limit_sem);
> +		/* Timeout likely occurs at disconnect (resulting in a leak) */
> +		ret = down_timeout_killable(&dev->urbs.limit_sem,
> +						FREE_URB_TIMEOUT);
>  		if (ret)
>  			break;

This is rather a hack.  Do you have an understanding of the underlying
bug?  Why is the driver waiting for things which will never happen?

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