On Tue, Sep 01, 2015 at 02:26:58PM -0700, Eric Dumazet wrote:
> On Tue, 2015-09-01 at 13:55 -0700, Martin KaFai Lau wrote:
> > On Tue, Sep 01, 2015 at 01:14:20PM -0700, Eric Dumazet wrote:
> > > It should not be a problem. refcnt is taken when/if necessary (skb
> > > queued on a qdisc for example)
> > >
> > > We have other uses of skb_dst_set_noref()
> > >
> > > Please describe the problem ?
> > The current ip6_tnl_dst_get() does not take the dst refcnt.
> >
> > If the dst is released after ip6_tnl_dst_get() and before
> > skb_dst_set_noref(), would it cause an issue?
>
> We are under rcu here, and a dst in a cache is protected by RCU by
> definition.
>
> skb_dst_set_noref() has following debugging clause, does it trigger for
> you ?
>
> WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
No. I did not see this.
I am probably missing something. Do you mean the rcu can
protect the followings:
ip6_tnl_dst_get()
dst_release()
dst_free() /* refcnt is 0 */
skb_dst_set_noref()
--------
or for DST_NOCACHE
ip6_tnl_dst_get()
dst_release() /* refcnt is 0 */
skb_dst_set_noref()
/* ip6tunnel_xmit()
* or its callees
* take a dst refcnt
*/
--------
or the above situation does not matter/will not happen?
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