On Wed, Jul 15, 2020 at 2:17 PM Florian Westphal <fw@xxxxxxxxx> wrote: > > Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > On Tue, 7 Jul 2020 12:55:08 +0800 wenxu@xxxxxxxxx wrote: > > > From: wenxu <wenxu@xxxxxxxxx> > > > > > > Add nf_ct_frag_gather and Make nf_ct_frag6_gather elide the CB clear > > > when packets are defragmented by connection tracking. This can make > > > each subsystem such as br_netfilter, openvswitch, act_ct do defrag > > > without restore the CB. > > > This also avoid serious crashes and problems in ct subsystem. > > > Because Some packet schedulers store pointers in the qdisc CB private > > > area and parallel accesses to the SKB. > > > > > > This series following up > > > http://patchwork.ozlabs.org/project/netdev/patch/1593422178-26949-1-git-send-email-wenxu@xxxxxxxxx/ > > > > > > patch1: add nf_ct_frag_gather elide the CB clear > > > patch2: make nf_ct_frag6_gather elide the CB clear > > > patch3: fix clobber qdisc_skb_cb in act_ct with defrag > > > > > > v2: resue some ip_defrag function in patch1 > > > > Florian, Cong - are you willing to venture an ack on these? Anyone? > > Nope, sorry. Reason is that I can't figure out the need for this series. > Taking a huge step back: > > http://patchwork.ozlabs.org/project/netdev/patch/1593422178-26949-1-git-send-email-wenxu@xxxxxxxxx/ > > That patch looks ok to me: > I understand the problem statement/commit message and I can see how its addressed. > > I don't understand why the CB clearing must be avoided. > > defrag assumes skb ownership -- e.g. it may realloc skb->data > (calls pskb_may_pull), it calls skb_orphan(), etc. > > AFAICS, tcf_classify makes same assumption -- exclusive ownership > and no parallel skb accesses. > > So, if in fact the "only" problem is the loss of > qdisc_skb_cb(skb)->pkt_len, then the other patch looks ok to me. > > If we indeed have parallel access, then I do not understand how > avoiding the memsets in the defrag path makes things any better > (see above wrt. skb pull and the like). +1 I don't see parallel access here either. skb can be cloned for packet socket or act_mirred, but its CB is cloned at the same time. Thanks.
