linux-kernel - Re: [PATCH] leds: Fix locking for WM8350

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Message-ID: <20081115173110.GD1523@ucw.cz>
Date:	Sat, 15 Nov 2008 18:31:10 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Richard Purdie <rpurdie@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: Fix locking for WM8350

On Thu 2008-11-13 14:57:49, Mark Brown wrote:
> LED API functions aren't allowed to sleep so we can't take a lock when
> setting the brightness of the LED.
> 
> Signed-off-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>
> ---
> 
> Sorry, I managed to drop this fix when moving the driver over to
> mainline for submission.  I'll roll it into the original patch in any
> future submissions.
> 
>  drivers/leds/leds-wm8350.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/leds/leds-wm8350.c b/drivers/leds/leds-wm8350.c
> index f3e5af3..283625c 100644
> --- a/drivers/leds/leds-wm8350.c
> +++ b/drivers/leds/leds-wm8350.c
> @@ -170,10 +170,7 @@ static void wm8350_led_set(struct led_classdev *led_cdev,
>  {
>  	struct wm8350_led *led = to_wm8350_led(led_cdev);
>  
> -	mutex_lock(&led->mutex);
>  	led->value = value;
> -	mutex_unlock(&led->mutex);
> -
>  	schedule_work(&led->work);
>  }

Unfortunately, now you write to value w/o locking -> races
possible. Maybe you need to make value atomic_t?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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