linux-kernel - Re: [PATCH 1/2] watchdog: update watchdog attributes atomically

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Message-ID: <20130726160745.GJ58219@redhat.com>
Date:	Fri, 26 Jul 2013 12:07:45 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/2] watchdog: update watchdog attributes atomically

On Fri, Jul 26, 2013 at 02:49:34PM +0200, Michal Hocko wrote:
> proc_dowatchdog doesn't synchronize multiple callers which
> might lead to confusion when two parallel callers might confuse
> watchdog_enable_all_cpus resp. watchdog_disable_all_cpus (e.g. watchdog
> gets enabled even if watchdog_thresh was set to 0 already).
> 
> This patch adds a local mutex which synchronizes callers to the sysctl
> handler.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Acked-by: Don Zickus <dzickus@...hat.com>


> ---
>  kernel/watchdog.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 1241d8c..2d64c02 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -520,13 +520,15 @@ int proc_dowatchdog(struct ctl_table *table, int write,
>  		    void __user *buffer, size_t *lenp, loff_t *ppos)
>  {
>  	int err, old_thresh, old_enabled;
> +	static DEFINE_MUTEX(watchdog_proc_mutex);
>  
> +	mutex_lock(&watchdog_proc_mutex);
>  	old_thresh = ACCESS_ONCE(watchdog_thresh);
>  	old_enabled = ACCESS_ONCE(watchdog_user_enabled);
>  
>  	err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>  	if (err || !write)
> -		return err;
> +		goto out;
>  
>  	set_sample_period();
>  	/*
> @@ -544,7 +546,8 @@ int proc_dowatchdog(struct ctl_table *table, int write,
>  		watchdog_thresh = old_thresh;
>  		watchdog_user_enabled = old_enabled;
>  	}
> -
> +out:
> +	mutex_unlock(&watchdog_proc_mutex);
>  	return err;
>  }
>  #endif /* CONFIG_SYSCTL */
> -- 
> 1.8.3.2
> 
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