linux-kernel - Re: [PATCH RFC] watchdog: core: don't try to stop device if not running

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Date:	Mon, 8 Apr 2013 09:48:57 +0200
From:	Hector Palacios <hector.palacios@...i.com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"wim@...ana.be" <wim@...ana.be>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] watchdog: core: don't try to stop device if not running

On 04/05/2013 08:34 PM, Guenter Roeck wrote:
> On Fri, Apr 05, 2013 at 06:09:44PM +0200, Hector Palacios wrote:
>> A watchdog device may be stopped from userspace using WDIOC_SETOPTIONS
>> ioctl and flag WDIOS_DISABLECARD. If the device is closed after this
>> operation, watchdog_release() is called and status bits checked for
>> stopping it. Besides, if the device has not been unregistered a critical
>> message "watchdog did not stop!" is printed, although the ioctl may have
>> successfully stopped it already.
>>
>> Without the patch a user application sample code like this will successfully
>> stop the watchdog, but the kernel will output the message
>> "watchdog did not stop!":
>>
>> 	wd_fd = open("/dev/watchdog", O_RDWR);
>>
>> 	flags = WDIOS_DISABLECARD;
>> 	ioctl(wd_fd, WDIOC_SETOPTIONS, &flags);
>>
>> 	close(wd_fd);
>>
>> Signed-off-by: Hector Palacios <hector.palacios@...i.com>
>
> How about the following patch instead ?
>
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 08b48bb..9775e8d 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -469,7 +469,9 @@ static int watchdog_release(struct inode *inode, struct file *file)
>   	 * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
>   	 * watchdog_stop will fail.
>   	 */
> -	if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
> +	if (!test_bit(WDOG_ACTIVE, &wdd->status))
> +		err = 0;
> +	else if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
>   	    !(wdd->info->options & WDIOF_MAGICCLOSE))
>   		err = watchdog_stop(wdd);
>
> Much less invasive and the result is the same.

I like the simplicity but it is kind of inverted logic to initially define err = 
-EBUSY only to turn it to zero later, so I'm rebuilding your approach like this:

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index ef8edec..a4163cd 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -463,16 +463,19 @@ out:
  static int watchdog_release(struct inode *inode, struct file *file)
  {
         struct watchdog_device *wdd = file->private_data;
-       int err = -EBUSY;
+       int err = 0;

         /*
          * We only stop the watchdog if we received the magic character
          * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
          * watchdog_stop will fail.
          */
-       if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
-           !(wdd->info->options & WDIOF_MAGICCLOSE))
+       if (test_bit(WDOG_ACTIVE, &wdd->status))
+               err = -EBUSY;
+       else if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) ||
+           !(wdd->info->options & WDIOF_MAGICCLOSE)) {
                 err = watchdog_stop(wdd);
+       }

         /* If the watchdog was not stopped, send a keepalive ping */


which makes the code more readable.
Thanks,
-- 
Héctor Palacios
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