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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 05:50 +0200
Message-ID <u84rL-6Qi-3@gated-at.bofh.it> (permalink)
References <u7Nhf-4j3-1@gated-at.bofh.it> <u7Nhg-4j3-15@gated-at.bofh.it> <u848p-6HH-7@gated-at.bofh.it> <u848p-6HH-9@gated-at.bofh.it>
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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.

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[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

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