linux-kernel - Re: [patch 1/2] hdaps: fix locking

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Date:	Sun, 14 Oct 2007 09:28:33 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthias Kaehlcke <matthias.kaehlcke@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/2] hdaps: fix locking

On Sun, Oct 14, 2007 at 09:25:23AM +0200, Nick Piggin wrote:
> Here are a couple of fixes for the hdaps driver. I have kind of been
> blocking out the bug traces caused by these (the 2nd patch, actually)
> thinking that it's one of those transient / churn things... but it's
> getting annoying now because I think it turns off lockdep. After this
> patch it no longer produces warnings, but I don't actually know if it
> does the right thing (because I don't really know what the driver
> does or how to test it anyway!).
> 

Ahh, forget that, I see the patch in -mm now, which should go in instead.


> ---
> 
> hdaps was using incorrect mutex_trylock return code.
> 
> Signed-off-by: Nick Piggin <npiggin@...e.de>
> 
> ---
> Index: linux-2.6/drivers/hwmon/hdaps.c
> ===================================================================
> --- linux-2.6.orig/drivers/hwmon/hdaps.c
> +++ linux-2.6/drivers/hwmon/hdaps.c
> @@ -328,22 +328,20 @@ static void hdaps_mousedev_poll(unsigned
>  	int x, y;
>  
>  	/* Cannot sleep.  Try nonblockingly.  If we fail, try again later. */
> -	if (mutex_trylock(&hdaps_mtx)) {
> -		mod_timer(&hdaps_timer,jiffies + HDAPS_POLL_PERIOD);
> -		return;
> -	}
> +	if (!mutex_trylock(&hdaps_mtx))
> +		goto out;
>  
>  	if (__hdaps_read_pair(HDAPS_PORT_XPOS, HDAPS_PORT_YPOS, &x, &y))
> -		goto out;
> +		goto out_lock;
>  
>  	input_report_abs(hdaps_idev, ABS_X, x - rest_x);
>  	input_report_abs(hdaps_idev, ABS_Y, y - rest_y);
>  	input_sync(hdaps_idev);
>  
> -	mod_timer(&hdaps_timer, jiffies + HDAPS_POLL_PERIOD);
> -
> -out:
> +out_lock:
>  	mutex_unlock(&hdaps_mtx);
> +out:
> +	mod_timer(&hdaps_timer, jiffies + HDAPS_POLL_PERIOD);
>  }
>  
>  
-
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