linux-kernel - Re: [PATCH 3/5] watchdog: implement error handling in update_watchdog_all

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Date:	Tue, 29 Sep 2015 07:40:46 +0100
From:	Aaron Tomlin <atomlin@...hat.com>
To:	Ulrich Obergfell <uobergfe@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	dzickus@...hat.com
Subject: Re: [PATCH 3/5] watchdog: implement error handling in
 update_watchdog_all_cpus() and callers

On Mon 2015-09-28 22:44 +0200, Ulrich Obergfell wrote:
> update_watchdog_all_cpus() now passes errors from watchdog_park_threads()
> up to functions in the call chain. This allows watchdog_enable_all_cpus()
> and proc_watchdog_update() to handle such errors too.
> 
> Signed-off-by: Ulrich Obergfell <uobergfe@...hat.com>
> ---
>  kernel/watchdog.c | 30 +++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index eb9527c..457113c 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -731,10 +731,17 @@ void lockup_detector_resume(void)
>  	mutex_unlock(&watchdog_proc_mutex);
>  }
>  
> -static void update_watchdog_all_cpus(void)
> +static int update_watchdog_all_cpus(void)
>  {
> -	watchdog_park_threads();
> +	int ret;
> +
> +	ret = watchdog_park_threads();
> +	if (ret)
> +		return ret;
> +
>  	watchdog_unpark_threads();
> +
> +	return 0;
>  }
>  
>  static int watchdog_enable_all_cpus(void)
> @@ -753,9 +760,17 @@ static int watchdog_enable_all_cpus(void)
>  		 * Enable/disable the lockup detectors or
>  		 * change the sample period 'on the fly'.
>  		 */
> -		update_watchdog_all_cpus();
> +		err = update_watchdog_all_cpus();
> +
> +		if (err) {
> +			watchdog_disable_all_cpus();
> +			pr_err("Failed to update lockup detectors, disabled\n");
> +		}
>  	}
>  
> +	if (err)
> +		watchdog_enabled = 0;
> +
>  	return err;
>  }
>  
> @@ -851,12 +866,13 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
>  		} while (cmpxchg(&watchdog_enabled, old, new) != old);
>  
>  		/*
> -		 * Update the run state of the lockup detectors.
> -		 * Restore 'watchdog_enabled' on failure.
> +		 * Update the run state of the lockup detectors. There is _no_
> +		 * need to check the value returned by proc_watchdog_update()
> +		 * and to restore the previous value of 'watchdog_enabled' as
> +		 * both lockup detectors are disabled if proc_watchdog_update()
> +		 * returns an error.
>  		 */
>  		err = proc_watchdog_update();
> -		if (err)
> -			watchdog_enabled = old;
>  	}
>  out:
>  	mutex_unlock(&watchdog_proc_mutex);

Reviewed-by: Aaron Tomlin <atomlin@...hat.com>

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