linux-kernel - Re: [PATCH v2] HID: i2c-hid: add mutex protecting open/close race

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Date:	Wed, 12 Dec 2012 18:27:26 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	Jean Delvare <khali@...ux-fr.org>, linux-input@...r.kernel.org,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] HID: i2c-hid: add mutex protecting open/close race

On Wed, 12 Dec 2012, Benjamin Tissoires wrote:

> We should not enter close function while someone else is in open.
> This mutex prevents this race.
> 
> There is also no need to override the ret value with -EIO in case of
> a failure of i2c_hid_set_power.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...il.com>
> Reviewed-by: Jean Delvare <khali@...ux-fr.org>
> ---
> 
> Changes in v2:
> * add mutex.h

Applied, thanks.

> 
> Cheers,
> Benjamin
> 
>  drivers/hid/i2c-hid/i2c-hid.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> index 6e1774c..9ef22244 100644
> --- a/drivers/hid/i2c-hid/i2c-hid.c
> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> @@ -33,6 +33,7 @@
>  #include <linux/jiffies.h>
>  #include <linux/kernel.h>
>  #include <linux/hid.h>
> +#include <linux/mutex.h>
>  
>  #include <linux/i2c/i2c-hid.h>
>  
> @@ -117,6 +118,8 @@ static const struct i2c_hid_cmd hid_set_power_cmd =	{ I2C_HID_CMD(0x08) };
>   * static const struct i2c_hid_cmd hid_set_protocol_cmd = { I2C_HID_CMD(0x07) };
>   */
>  
> +static DEFINE_MUTEX(i2c_hid_open_mut);
> +
>  /* The main device structure */
>  struct i2c_hid {
>  	struct i2c_client	*client;	/* i2c client */
> @@ -641,17 +644,20 @@ static int i2c_hid_open(struct hid_device *hid)
>  {
>  	struct i2c_client *client = hid->driver_data;
>  	struct i2c_hid *ihid = i2c_get_clientdata(client);
> -	int ret;
> +	int ret = 0;
>  
> +	mutex_lock(&i2c_hid_open_mut);
>  	if (!hid->open++) {
>  		ret = i2c_hid_set_power(client, I2C_HID_PWR_ON);
>  		if (ret) {
>  			hid->open--;
> -			return -EIO;
> +			goto done;
>  		}
>  		set_bit(I2C_HID_STARTED, &ihid->flags);
>  	}
> -	return 0;
> +done:
> +	mutex_unlock(&i2c_hid_open_mut);
> +	return ret;
>  }
>  
>  static void i2c_hid_close(struct hid_device *hid)
> @@ -663,12 +669,14 @@ static void i2c_hid_close(struct hid_device *hid)
>  	 * data acquistion due to a resumption we no longer
>  	 * care about
>  	 */
> +	mutex_lock(&i2c_hid_open_mut);
>  	if (!--hid->open) {
>  		clear_bit(I2C_HID_STARTED, &ihid->flags);
>  
>  		/* Save some power */
>  		i2c_hid_set_power(client, I2C_HID_PWR_SLEEP);
>  	}
> +	mutex_unlock(&i2c_hid_open_mut);
>  }
>  
>  static int i2c_hid_power(struct hid_device *hid, int lvl)
> -- 
> 1.8.0.2
> 

-- 
Jiri Kosina
SUSE Labs
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