Re: [PATCH net-next 3/3] tap: XDP support

From	"Michael S. Tsirkin" <mst@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH net-next 3/3] tap: XDP support
Date	2017-07-28 06:10 +0200
Message-ID	<u84L7-7bU-1@gated-at.bofh.it> (permalink)
References	(1 earlier) <u7Nhg-4j3-15@gated-at.bofh.it> <u848p-6HH-7@gated-at.bofh.it> <u848p-6HH-9@gated-at.bofh.it> <u84rL-6Qi-3@gated-at.bofh.it> <u84Br-6TA-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Fri, Jul 28, 2017 at 11:50:45AM +0800, Jason Wang wrote:
> 
> 
> On 2017年07月28日 11:46, Michael S. Tsirkin wrote:
> > On Fri, Jul 28, 2017 at 11:28:54AM +0800, Jason Wang wrote:
> > > > > +	old_prog = rtnl_dereference(tun->xdp_prog);
> > > > > +	if (old_prog)
> > > > > +		bpf_prog_put(old_prog);
> > > > > +	rcu_assign_pointer(tun->xdp_prog, prog);
> > > > Is this OK?  Could this lead to the program getting freed and then
> > > > datapath accessing a stale pointer?  I mean in the scenario where the
> > > > process gets pre-empted between the bpf_prog_put() and
> > > > rcu_assign_pointer()?
> > > Will call bpf_prog_put() after rcu_assign_pointer().
> > I suspect you need to sync RCU or something before that.
> 
> __bpf_prog_put() will do call_rcu(), so looks like it was ok.
> 
> Thanks

True - I missed that.

-- 
MST

Thread

[PATCH net-next 0/3] XDP support for tap Jason Wang <jasowang@redhat.com> - 2017-07-27 11:30 +0200
  [PATCH net-next 1/3] tap: use build_skb() for small packet Jason Wang <jasowang@redhat.com> - 2017-07-27 11:30 +0200
  [PATCH net-next 2/3] net: export some generic xdp helpers Jason Wang <jasowang@redhat.com> - 2017-07-27 11:30 +0200
  [PATCH net-next 3/3] tap: XDP support Jason Wang <jasowang@redhat.com> - 2017-07-27 11:30 +0200
    Re: [PATCH net-next 3/3] tap: XDP support Jason Wang <jasowang@redhat.com> - 2017-07-28 05:30 +0200
      Re: [PATCH net-next 3/3] tap: XDP support "Michael S. Tsirkin" <mst@redhat.com> - 2017-07-28 05:50 +0200
        Re: [PATCH net-next 3/3] tap: XDP support Jakub Kicinski <kubakici@wp.pl> - 2017-07-28 06:00 +0200
        Re: [PATCH net-next 3/3] tap: XDP support Jason Wang <jasowang@redhat.com> - 2017-07-28 06:00 +0200
          Re: [PATCH net-next 3/3] tap: XDP support "Michael S. Tsirkin" <mst@redhat.com> - 2017-07-28 06:10 +0200
        Re: [PATCH net-next 3/3] tap: XDP support Daniel Borkmann <daniel@iogearbox.net> - 2017-07-28 17:20 +0200
    Re: [PATCH net-next 3/3] tap: XDP support Jakub Kicinski <kubakici@wp.pl> - 2017-07-28 05:30 +0200

csiph-web