On Tue, 2015-09-01 at 15:25 -0700, Martin KaFai Lau wrote: > 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() >
Yes, this is protected by normal rcu rules. dst wont be freed until all cpus exit their rcu read sections. > -------- > > 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? > -- You should take a look at following commits for a bit of history 10e2eb878f3ca07ac2f05fa5ca5e6c4c9174a27a dbfc4fb7d578d4f224faa6b60deb40804dfdc1b1 f88649721268999bdff09777847080a52004f691 6c7e7610ff6888ea15a901fbcb30c5d461816b34 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
