linux-kernel - Re: [PATCHv2] bridge: disable snooping if there is no querier

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Date:	Thu, 25 Jul 2013 09:01:40 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Linus Lüssing <linus.luessing@....de>
Cc:	bridge@...ts.linux-foundation.org,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Cong Wang <amwang@...hat.com>,
	Adam Baker <linux@...er-net.org.uk>
Subject: Re: [PATCHv2] bridge: disable snooping if there is no querier

On Thu, 25 Jul 2013 15:56:20 +0200
Linus Lüssing <linus.luessing@....de> wrote:

>  
> +static void br_multicast_update_querier_timer(struct net_bridge *br,
> +					      unsigned long max_delay)
> +{
> +	if (!timer_pending(&br->multicast_querier_timer))
> +		atomic64_set(&br->multicast_querier_delay_time,
> +			     jiffies + max_delay);
> +
> +	mod_timer(&br->multicast_querier_timer,
> +		  jiffies + br->multicast_querier_interval);
> +}
> +

Isn't this test racing with timer expiration.

static void br_multicast_update_querier_timer(struct net_bridge *br,
					      unsigned long max_delay)
{
	if (!timer_pending(&br->multicast_querier_timer))
		atomic64_set(&br->multicast_querier_delay_time,
			     jiffies + max_delay);
What if timer completes here?

	mod_timer(&br->multicast_querier_timer,
		  jiffies + br->multicast_querier_interval);
}


And another race if timer goes off?

static void br_multicast_update_querier_timer(struct net_bridge *br,
					      unsigned long max_delay)
{
	if (!timer_pending(&br->multicast_querier_timer))
		atomic64_set(&br->multicast_querier_delay_time,
			     jiffies + max_delay);
Timer fires here...?

	mod_timer(&br->multicast_querier_timer,
		  jiffies + br->multicast_querier_interval);
}
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