On Tue, 2017-08-15 at 22:45 +0300, Julian Anastasov wrote:
> Hello,
>
> On Tue, 15 Aug 2017, Eric Dumazet wrote:
>
> > Please try this :
> > diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> > index
> > 16a1a4c4eb57fa1147f230916e2e62e18ef89562..95e0d7702029b583de8229e3c3eb923f6395b072
> > 100644
> > --- a/net/core/neighbour.c
> > +++ b/net/core/neighbour.c
> > @@ -991,14 +991,18 @@ static void neigh_timer_handler(unsigned long arg)
> >
> > int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
> > {
> > - int rc;
> > bool immediate_probe = false;
> > + int rc;
> > +
> > + /* We _should_ test this under write_lock_bh(&neigh->lock),
> > + * but this is too costly.
> > + */
> > + if (READ_ONCE(neigh->nud_state) & (NUD_CONNECTED | NUD_DELAY |
> > NUD_PROBE))
> > + return 0;
>
> The same fast check is already done in the only caller,
> neigh_event_send. Now we risk to enter the
> 'if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {' block...
Right you are.
It must be possible to add a fast path without locks.
(say if jiffies has not changed before last state change)
