From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
willemdebruijn.kernel@gmail.com, tom@herbertland.com
Subject: Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection method
Date: Thu, 2 Nov 2017 11:45:39 +0800 [thread overview]
Message-ID: <30aa1418-9253-5721-a489-84cd6e1722c5@redhat.com> (raw)
In-Reply-To: <20171101150458-mutt-send-email-mst@kernel.org>
On 2017年11月01日 21:59, Michael S. Tsirkin wrote:
> On Wed, Nov 01, 2017 at 09:02:03PM +0800, Jason Wang wrote:
>>
>> 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().
> Is the call from tun_free_netdev under rtnl too?
Looks not, need hold rtnl_lock() in tun_free_netdev in next version.
>
>>> 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
> Not the wait - expedited is not a good thing to allow unpriveledged
> userspace to do, it interrupts all VMs running on the same box.
Good point.
>
> We could use a callback though the docs warn userspace can use that
> to cause a DOS and needs to be limited.
>
>
Will do this in next version.
Thanks
next prev parent reply other threads:[~2017-11-02 3:45 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 10:32 [PATCH net-next V2 0/3] support changing steering policies in tuntap Jason Wang
2017-10-31 10:32 ` [PATCH net-next V2 1/3] tun: abstract flow steering logic Jason Wang
2017-11-02 1:11 ` Willem de Bruijn
2017-11-02 3:43 ` Jason Wang
2017-11-02 3:45 ` Michael S. Tsirkin
2017-11-02 3:51 ` Jason Wang
2017-11-03 8:49 ` Willem de Bruijn
2017-10-31 10:32 ` [PATCH net-next V2 2/3] tun: introduce ioctls to set and get steering policies Jason Wang
2017-11-02 1:15 ` Willem de Bruijn
2017-10-31 10:32 ` [PATCH net-next V2 3/3] tun: add eBPF based queue selection method Jason Wang
2017-10-31 16:45 ` Michael S. Tsirkin
2017-11-01 13:02 ` Jason Wang
2017-11-01 13:59 ` Michael S. Tsirkin
2017-11-01 19:12 ` Alexei Starovoitov
2017-11-02 3:24 ` Jason Wang
2017-11-02 3:45 ` Jason Wang [this message]
2017-11-03 8:56 ` Willem de Bruijn
2017-11-03 23:56 ` Willem de Bruijn
2017-11-08 5:28 ` Jason Wang
2017-11-08 5:43 ` Michael S. Tsirkin
2017-11-08 11:13 ` Jason Wang
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