netdev - Re: [PATCH v2] VLAN, support ingress/egress priority map flushing

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Date:   Mon, 13 Mar 2017 21:33:52 +0100
From:   Thierry Du Tre <thierry@...ystems.be>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, Ben Greear <greearb@...delatech.com>
Subject: Re: [PATCH v2] VLAN, support ingress/egress priority map flushing

On 13-03-17 16:28, Eric Dumazet wrote:
> On Mon, 2017-03-13 at 15:36 +0100, Thierry Du Tre wrote:
>
>> +void vlan_dev_flush_egress_priority(const struct net_device *dev)
>> +{
>> +	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
>> +	struct vlan_priority_tci_mapping *mp;
>> +	int i;
>> +
>> +	for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
>> +		while ((mp = vlan->egress_priority_map[i]) != NULL) {
>> +			vlan->egress_priority_map[i] = mp->next;
>> +			kfree(mp);
>> +		}
>> +	}
>> +	vlan->nr_egress_mappings = 0;
>> +}
>
> Are you doing this on a live device ?
>
> Looks you'll need proper RCU support then.
>
> Otherwise, crashes will happen, say in egress_priority_map()
>
> smp_rmb() wont be enough if items can now be destroyed.
Yes, good point about the smp concurrency.
I wrongly assumed there was already some locking mechanism in place to 
protect these structures.

Let me take a look at this and I'll come back with a new proposal.

--
Thierry