[PATCH v2] watchdog: core: don't try to stop device if not running

[PATCH v2] watchdog: core: don't try to stop device if not running

[Hector Palacios]

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@digi.com>
---

Changes from v1:
- Make it less intrusive with 'if/else if' clauses
- Change the logic of 'err' variable for better readability of code
- Remove one-liner if brackets that broke coding sytle

 drivers/watchdog/watchdog_dev.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index ef8edec..8e0f1b8 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -463,15 +463,17 @@ 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 */
-- 
1.8.2

Re: [PATCH v2] watchdog: core: don't try to stop device if not running

[Guenter Roeck]

On Mon, Apr 08, 2013 at 11:10:58AM +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@digi.com>
> ---
> 
> Changes from v1:
> - Make it less intrusive with 'if/else if' clauses
> - Change the logic of 'err' variable for better readability of code
> - Remove one-liner if brackets that broke coding sytle
> 
>  drivers/watchdog/watchdog_dev.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index ef8edec..8e0f1b8 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -463,15 +463,17 @@ 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);
>  
Looking at it again, it is now broken and fails with EBUSY if WDOG_ACTIVE is
set, and it tries to stop the watchdog if it is already stopped.

Guenter

Re: [PATCH v2] watchdog: core: don't try to stop device if not running

[Hector Palacios]

On 04/08/2013 03:41 PM, Guenter Roeck wrote:
> On Mon, Apr 08, 2013 at 11:10:58AM +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@digi.com>
>> ---
>>
>> Changes from v1:
>> - Make it less intrusive with 'if/else if' clauses
>> - Change the logic of 'err' variable for better readability of code
>> - Remove one-liner if brackets that broke coding sytle
>>
>>   drivers/watchdog/watchdog_dev.c | 8 +++++---
>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
>> index ef8edec..8e0f1b8 100644
>> --- a/drivers/watchdog/watchdog_dev.c
>> +++ b/drivers/watchdog/watchdog_dev.c
>> @@ -463,15 +463,17 @@ 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);
>>
> Looking at it again, it is now broken and fails with EBUSY if WDOG_ACTIVE is
> set, and it tries to stop the watchdog if it is already stopped.

You are right, good catch! So your patch version wins.
Thank you
-- 
Héctor Palacios
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