netdev - Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection method

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Message-ID: <43c86606-2911-768d-704f-8b25e04cb47b@redhat.com>
Date:   Wed, 1 Nov 2017 21:02:03 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        willemdebruijn.kernel@...il.com, tom@...bertland.com
Subject: Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection
 method



On 2017年11月01日 00:45, Michael S. Tsirkin wrote:
>> +static void __tun_set_steering_ebpf(struct tun_struct *tun,
>> +				    struct bpf_prog *new)
>> +{
>> +	struct bpf_prog *old;
>> +
>> +	old = rtnl_dereference(tun->steering_prog);
>> +	rcu_assign_pointer(tun->steering_prog, new);
>> +
>> +	if (old) {
>> +		synchronize_net();
>> +		bpf_prog_destroy(old);
>> +	}
>> +}
>> +
> Is this really called under rtnl?

Yes it is __tun_chr_ioctl() will call rtnl_lock().

> If no then rtnl_dereference
> is wrong. If yes I'm not sure you can call synchronize_net
> under rtnl.
>

Are you worrying about the long wait? Looking at synchronize_net(), it does:

void synchronize_net(void)
{
     might_sleep();
     if (rtnl_is_locked())
         synchronize_rcu_expedited();
     else
         synchronize_rcu();
}
EXPORT_SYMBOL(synchronize_net);

Thanks