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

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Message-ID: <20130719161047.GN126784@redhat.com>
Date:	Fri, 19 Jul 2013 12:10:48 -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: [RFC 1/2] watchdog: update watchdog attributes atomically

On Fri, Jul 19, 2013 at 11:04:58AM +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.

Looks fine by me, except one little nitpick..

> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> ---
>  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);

Should we just make this global instead of hiding it as a static inside a
function.  I don't know the kernel rules for deciding which approach makes
sense.  I know it is the same result in either case...

Cheers,
Don
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