[patch] reducing arp locking

[Fabien Thomas]

Le 9 nov. 2012 à 17:43, Ingo Flaschberger a écrit :

> Am 09.11.2012 15:03, schrieb Fabien Thomas:
>> In in_arpinput only exclusive access to the entry is taken during the update no IF_AFDATA_LOCK that's why i was surprised.
> 
> what about this:

I'm not against optimizing but an API that seems clear (correct this if i'm wrong):
- one lock for list modification
- one RW lock for lle entry access
- one refcount for ptr unref

is now a lot more unclear and from my point of view dangerous.

My next question is why do we need a per entry lock if we use the table lock to protect entry access?

Fabien
 
> --
> --- /usr/src/sys/netinet/if_ether.c_org 2012-11-09 16:15:43.000000000 +0000
> +++ /usr/src/sys/netinet/if_ether.c     2012-11-09 16:16:37.000000000 +0000
> @@ -685,7 +685,7 @@
>        flags |= LLE_EXCLUSIVE;
>        IF_AFDATA_LOCK(ifp);
>        la = lla_lookup(LLTABLE(ifp), flags, (struct sockaddr *)&sin);
> -       IF_AFDATA_UNLOCK(ifp);
> +
>        if (la != NULL) {
>                /* the following is not an error when doing bridging */
>                if (!bridged && la->lle_tbl->llt_ifp != ifp && !carp_match) {
> @@ -697,12 +697,14 @@
>                                    ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
>                                    ifp->if_xname);
>                        LLE_WUNLOCK(la);
> +                       IF_AFDATA_UNLOCK(ifp);
>                        goto reply;
>                }
>                if ((la->la_flags & LLE_VALID) &&
>                    bcmp(ar_sha(ah), &la->ll_addr, ifp->if_addrlen)) {
>                        if (la->la_flags & LLE_STATIC) {
>                                LLE_WUNLOCK(la);
> +                               IF_AFDATA_UNLOCK(ifp);
>                                if (log_arp_permanent_modify)
>                                        log(LOG_ERR,
>                                            "arp: %*D attempts to modify "
> @@ -725,6 +727,7 @@
> 
>                if (ifp->if_addrlen != ah->ar_hln) {
>                        LLE_WUNLOCK(la);
> +                       IF_AFDATA_UNLOCK(ifp);
>                        log(LOG_WARNING, "arp from %*D: addr len: new %d, "
>                            "i/f %d (ignored)\n", ifp->if_addrlen,
>                            (u_char *) ar_sha(ah), ":", ah->ar_hln,
> @@ -763,14 +766,19 @@
>                        la->la_numheld = 0;
>                        memcpy(&sa, L3_ADDR(la), sizeof(sa));
>                        LLE_WUNLOCK(la);
> +                       IF_AFDATA_UNLOCK(ifp);
>                        for (; m_hold != NULL; m_hold = m_hold_next) {
>                                m_hold_next = m_hold->m_nextpkt;
>                                m_hold->m_nextpkt = NULL;
>                                (*ifp->if_output)(ifp, m_hold, &sa, NULL);
>                        }
> -               } else
> +               } else {
>                        LLE_WUNLOCK(la);
> -       }
> +                       IF_AFDATA_UNLOCK(ifp);
> +                }
> +       } else {
> +               IF_AFDATA_UNLOCK(ifp);
> +        }
> reply:
>        if (op != ARPOP_REQUEST)
>                goto drop;
> --
> 
> Kind regards,
>    Ingo Flaschberger
> 
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