Use epoch(9) for rtentries to simplify control plane operations.

Currently the only reason of refcounting rtentries is the need to report
 the rtable operation details immediately after the execution.
Delaying rtentry reclamation allows to stop refcounting and simplify the code.
Additionally, this change allows to reimplement rib_lookup_info(), which
 is used by some of the customers to get the matching prefix along
 with nexthops, in more efficient way.

The change keeps per-vnet rtzone uma zone. It adds nh_vnet field to
 nhop_priv to be able to reliably set curvnet even during vnet teardown.
Rest of the reference counting code will be removed in the D24867 .

Differential Revision:	https://reviews.freebsd.org/D24866

sys/fs/nfsclient/nfs_clvfsops.c

@@ -465,18 +465,21 @@ nfs_mountroot(struct mount *mp)
 	if (nd->mygateway.sin_len != 0 &&
 	    nd->mygateway.sin_addr.s_addr != 0) {
 		struct sockaddr_in mask, sin;
+		struct epoch_tracker et;
 
 		bzero((caddr_t)&mask, sizeof(mask));
 		sin = mask;
 		sin.sin_family = AF_INET;
 		sin.sin_len = sizeof(sin);
                 /* XXX MRT use table 0 for this sort of thing */
+		NET_EPOCH_ENTER(et);
 		CURVNET_SET(TD_TO_VNET(td));
 		error = rtrequest_fib(RTM_ADD, (struct sockaddr *)&sin,
 		    (struct sockaddr *)&nd->mygateway,
 		    (struct sockaddr *)&mask,
 		    RTF_UP | RTF_GATEWAY, NULL, RT_DEFAULT_FIB);
 		CURVNET_RESTORE();
+		NET_EPOCH_EXIT(et);
 		if (error)
 			panic("nfs_mountroot: RTM_ADD: %d", error);
 	}

sys/net/if.c

@@ -1854,18 +1854,17 @@ ifa_maintain_loopback_route(int cmd, const char *otype, struct ifaddr *ifa,
 
 	ifp = ifa->ifa_ifp;
 
+	NET_EPOCH_ENTER(et);
 	bzero(&info, sizeof(info));
 	if (cmd != RTM_DELETE)
 		info.rti_ifp = V_loif;
 	if (cmd == RTM_ADD) {
 		/* explicitly specify (loopback) ifa */
 		if (info.rti_ifp != NULL) {
-			NET_EPOCH_ENTER(et);
 			rti_ifa = ifaof_ifpforaddr(ifa->ifa_addr, info.rti_ifp);
 			if (rti_ifa != NULL)
 				ifa_ref(rti_ifa);
 			info.rti_ifa = rti_ifa;
-			NET_EPOCH_EXIT(et);
 		}
 	}
 	info.rti_flags = ifa->ifa_flags | RTF_HOST | RTF_STATIC | RTF_PINNED;
@@ -1874,6 +1873,7 @@ ifa_maintain_loopback_route(int cmd, const char *otype, struct ifaddr *ifa,
 	link_init_sdl(ifp, (struct sockaddr *)&null_sdl, ifp->if_type);
 
 	error = rtrequest1_fib(cmd, &info, NULL, ifp->if_fib);
+	NET_EPOCH_EXIT(et);
 
 	if (rti_ifa != NULL)
 		ifa_free(rti_ifa);

sys/net/route.c

@@ -120,9 +120,6 @@ VNET_PCPUSTAT_SYSUNINIT(rtstat);
 VNET_DEFINE(struct rib_head *, rt_tables);
 #define	V_rt_tables	VNET(rt_tables)
 
-VNET_DEFINE(int, rttrash);		/* routes not in table but not freed */
-#define	V_rttrash	VNET(rttrash)
-
 
 /*
  * Convert a 'struct radix_node *' to a 'struct rtentry *'.
@@ -148,6 +145,7 @@ static int rt_ifdelroute(const struct rtentry *rt, const struct nhop_object *,
 static struct rtentry *rt_unlinkrte(struct rib_head *rnh,
     struct rt_addrinfo *info, int *perror);
 static void rt_notifydelete(struct rtentry *rt, struct rt_addrinfo *info);
+static void destroy_rtentry_epoch(epoch_context_t ctx);
 #ifdef RADIX_MPATH
 static struct radix_node *rt_mpath_unlink(struct rib_head *rnh,
     struct rt_addrinfo *info, struct rtentry *rto, int *perror);
@@ -332,6 +330,16 @@ vnet_route_uninit(const void *unused __unused)
 		}
 	}
 
+	/*
+	 * dom_rtdetach calls rt_table_destroy(), which
+	 *  schedules deletion for all rtentries, nexthops and control
+	 *  structures. Wait for the destruction callbacks to fire.
+	 * Note that this should result in freeing all rtentries, but
+	 *  nexthops deletions will be scheduled for the next epoch run
+	 *  and will be completed after vnet teardown.
+	 */
+	epoch_drain_callbacks(net_epoch_preempt);
+
 	free(V_rt_tables, M_RTABLE);
 	uma_zdestroy(V_rtzone);
 }
@@ -449,41 +457,54 @@ rtfree(struct rtentry *rt)
 	if ((rt->rt_flags & RTF_UP) == 0) {
 		if (rt->rt_nodes->rn_flags & (RNF_ACTIVE | RNF_ROOT))
 			panic("rtfree 2");
-		/*
-		 * the rtentry must have been removed from the routing table
-		 * so it is represented in rttrash.. remove that now.
-		 */
-		V_rttrash--;
 #ifdef	DIAGNOSTIC
 		if (rt->rt_refcnt < 0) {
 			printf("rtfree: %p not freed (neg refs)\n", rt);
 			goto done;
 		}
 #endif
-
-		/* Unreference nexthop */
-		nhop_free(rt->rt_nhop);
+		epoch_call(net_epoch_preempt, destroy_rtentry_epoch,
+		    &rt->rt_epoch_ctx);
 
 		/*
-		 * and the rtentry itself of course
+		 * FALLTHROUGH to RT_UNLOCK() so the reporting functions
+		 * have consistent behaviour of operating on unlocked entry.
 		 */
-		uma_zfree(V_rtzone, rt);
-		return;
 	}
 done:
 	RT_UNLOCK(rt);
 }
 
+static void
+destroy_rtentry(struct rtentry *rt)
+{
+
+	/*
+	 * At this moment rnh, nh_control may be already freed.
+	 * nhop interface may have been migrated to a different vnet.
+	 * Use vnet stored in the nexthop to delete the entry.
+	 */
+	CURVNET_SET(nhop_get_vnet(rt->rt_nhop));
+
+	/* Unreference nexthop */
+	nhop_free(rt->rt_nhop);
+
+	uma_zfree(V_rtzone, rt);
+
+	CURVNET_RESTORE();
+}
+
 /*
- * Temporary RTFREE() function wrapper.
- *  Intended to use in control plane code to
- *  avoid exposing internal layout of 'struct rtentry'.
+ * Epoch callback indicating rtentry is safe to destroy
  */
-void
-rtfree_func(struct rtentry *rt)
+static void
+destroy_rtentry_epoch(epoch_context_t ctx)
 {
+	struct rtentry *rt;
+
+	rt = __containerof(ctx, struct rtentry, rt_epoch_ctx);
 
-	RTFREE(rt);
+	destroy_rtentry(rt);
 }
 
 /*
@@ -546,7 +567,7 @@ rib_add_redirect(u_int fibnum, struct sockaddr *dst, struct sockaddr *gateway,
 
 	RT_LOCK(rt);
 	flags = rt->rt_flags;
-	RTFREE_LOCKED(rt);
+	RT_UNLOCK(rt);
 
 	RTSTAT_INC(rts_dynamic);
 
@@ -1112,13 +1133,6 @@ rt_notifydelete(struct rtentry *rt, struct rt_addrinfo *info)
 	ifa = rt->rt_nhop->nh_ifa;
 	if (ifa != NULL && ifa->ifa_rtrequest != NULL)
 		ifa->ifa_rtrequest(RTM_DELETE, rt, rt->rt_nhop, info);
-
-	/*
-	 * One more rtentry floating around that is not
-	 * linked to the routing table. rttrash will be decremented
-	 * when RTFREE(rt) is eventually called.
-	 */
-	V_rttrash++;
 }
 
 
@@ -1386,6 +1400,7 @@ rtrequest1_fib(int req, struct rt_addrinfo *info, struct rtentry **ret_nrt,
 
 	KASSERT((fibnum < rt_numfibs), ("rtrequest1_fib: bad fibnum"));
 	KASSERT((info->rti_flags & RTF_RNH_LOCKED) == 0, ("rtrequest1_fib: locked"));
+	NET_EPOCH_ASSERT();
 
 	dst = info->rti_info[RTAX_DST];
 
@@ -1580,13 +1595,10 @@ add_route(struct rib_head *rnh, struct rt_addrinfo *info,
 		ifa->ifa_rtrequest(RTM_ADD, rt, rt->rt_nhop, info);
 
 	/*
-	 * actually return a resultant rtentry and
-	 * give the caller a single reference.
+	 * actually return a resultant rtentry
 	 */
-	if (ret_nrt) {
+	if (ret_nrt)
 		*ret_nrt = rt;
-		RT_ADDREF(rt);
-	}
 	rnh->rnh_gen++;		/* Routing table updated */
 	RT_UNLOCK(rt);
 
@@ -1622,15 +1634,13 @@ del_route(struct rib_head *rnh, struct rt_addrinfo *info,
 
 	/*
 	 * If the caller wants it, then it can have it,
-	 * but it's up to it to free the rtentry as we won't be
-	 * doing it.
+	 * the entry will be deleted after the end of the current epoch.
 	 */
-	if (ret_nrt) {
+	if (ret_nrt)
 		*ret_nrt = rt;
-		RT_UNLOCK(rt);
-	} else
-		RTFREE_LOCKED(rt);
-
+
+	RTFREE_LOCKED(rt);
+
 	return (0);
 }
 
@@ -1736,10 +1746,8 @@ change_route_one(struct rib_head *rnh, struct rt_addrinfo *info,
 	if ((nh_orig->nh_ifa != nh->nh_ifa) && nh_orig->nh_ifa->ifa_rtrequest)
 		nh_orig->nh_ifa->ifa_rtrequest(RTM_DELETE, rt, nh_orig, info);
 
-	if (ret_nrt != NULL) {
+	if (ret_nrt != NULL)
 		*ret_nrt = rt;
-		RT_ADDREF(rt);
-	}
 
 	RT_UNLOCK(rt);
 
@@ -1757,16 +1765,13 @@ static int
 change_route(struct rib_head *rnh, struct rt_addrinfo *info,
     struct rtentry **ret_nrt)
 {
-	struct epoch_tracker et;
 	int error;
 
 	/* Check if updated gateway exists */
 	if ((info->rti_flags & RTF_GATEWAY) &&
 	    (info->rti_info[RTAX_GATEWAY] == NULL))
 		return (EINVAL);
 
-	NET_EPOCH_ENTER(et);
-
 	/*
 	 * route change is done in multiple steps, with dropping and
 	 * reacquiring lock. In the situations with multiple processes
@@ -1779,7 +1784,6 @@ change_route(struct rib_head *rnh, struct rt_addrinfo *info,
 		if (error != EAGAIN)
 			break;
 	}
-	NET_EPOCH_EXIT(et);
 
 	return (error);
 }
@@ -1825,6 +1829,7 @@ static inline  int
 rtinit1(struct ifaddr *ifa, int cmd, int flags, int fibnum)
 {
 	RIB_RLOCK_TRACKER;
+	struct epoch_tracker et;
 	struct sockaddr *dst;
 	struct sockaddr *netmask;
 	struct rtentry *rt = NULL;
@@ -1957,38 +1962,18 @@ rtinit1(struct ifaddr *ifa, int cmd, int flags, int fibnum)
 		else
 			info.rti_info[RTAX_GATEWAY] = ifa->ifa_addr;
 		info.rti_info[RTAX_NETMASK] = netmask;
+		NET_EPOCH_ENTER(et);
 		error = rtrequest1_fib(cmd, &info, &rt, fibnum);
 		if (error == 0 && rt != NULL) {
 			/*
 			 * notify any listening routing agents of the change
 			 */
-			RT_LOCK(rt);
 
 			/* TODO: interface routes/aliases */
-			RT_ADDREF(rt);
-			RT_UNLOCK(rt);
 			rt_newaddrmsg_fib(cmd, ifa, rt, fibnum);
-			RT_LOCK(rt);
-			RT_REMREF(rt);
-			if (cmd == RTM_DELETE) {
-				/*
-				 * If we are deleting, and we found an entry,
-				 * then it's been removed from the tree..
-				 * now throw it away.
-				 */
-				RTFREE_LOCKED(rt);
-			} else {
-				if (cmd == RTM_ADD) {
-					/*
-					 * We just wanted to add it..
-					 * we don't actually need a reference.
-					 */
-					RT_REMREF(rt);
-				}
-				RT_UNLOCK(rt);
-			}
 			didwork = 1;
 		}
+		NET_EPOCH_EXIT(et);
 		if (error)
 			a_failure = error;
 	}

sys/net/route.h

@@ -332,8 +332,6 @@ struct rt_addrinfo {
 #define RT_LINK_IS_UP(ifp)	(!((ifp)->if_capabilities & IFCAP_LINKSTATE) \
 				 || (ifp)->if_link_state == LINK_STATE_UP)
 
-#define	RTFREE_FUNC(_rt)	rtfree_func(_rt)
-
 #define	RO_NHFREE(_ro) do {					\
 	if ((_ro)->ro_nh) {					\
 		NH_FREE((_ro)->ro_nh);				\

sys/net/route/nhop.h

@@ -176,6 +176,7 @@ struct rib_head;
 uint32_t nhop_get_idx(const struct nhop_object *nh);
 enum nhop_type nhop_get_type(const struct nhop_object *nh);
 int nhop_get_rtflags(const struct nhop_object *nh);
+struct vnet *nhop_get_vnet(const struct nhop_object *nh);
 
 #endif /* _KERNEL */
 

sys/net/route/nhop_ctl.c

@@ -500,6 +500,9 @@ finalize_nhop(struct nh_control *ctl, struct rt_addrinfo *info,
 		return (ENOMEM);
 	}
 
+	/* Save vnet to ease destruction */
+	nh_priv->nh_vnet = curvnet;
+
 	/* Reference external objects and calculate (referenced) ifa */
 	if_ref(nh->nh_ifp);
 	ifa_ref(nh->nh_ifa);
@@ -698,6 +701,13 @@ nhop_set_rtflags(struct nhop_object *nh, int rt_flags)
 	nh->nh_priv->rt_flags = rt_flags;
 }
 
+struct vnet *
+nhop_get_vnet(const struct nhop_object *nh)
+{
+
+	return (nh->nh_priv->nh_vnet);
+}
+
 void
 nhops_update_ifmtu(struct rib_head *rh, struct ifnet *ifp, uint32_t mtu)
 {

sys/net/route/nhop_var.h

@@ -78,6 +78,7 @@ struct nhop_priv {
 	struct nhop_object	*nh;		/* backreference to the dataplane nhop */
 	struct nh_control	*nh_control;	/* backreference to the rnh */
 	struct nhop_priv	*nh_next;	/* hash table membership */
+	struct vnet		*nh_vnet;	/* vnet nhop belongs to */
 	struct epoch_context	nh_epoch_ctx;	/* epoch data for nhop */
 };
 

sys/net/route/route_var.h

@@ -35,6 +35,7 @@
 #ifndef RNF_NORMAL
 #include <net/radix.h>
 #endif
+#include <sys/epoch.h>
 #include <netinet/in.h>		/* struct sockaddr_in */
 #include <sys/counter.h>
 
@@ -148,6 +149,7 @@ struct rtentry {
 #define	rt_endzero	rt_mtx
 	struct mtx	rt_mtx;		/* mutex for routing entry */
 	struct rtentry	*rt_chain;	/* pointer to next rtentry to delete */
+	struct epoch_context	rt_epoch_ctx;	/* net epoch tracker */
 };
 
 #define	RT_LOCK_INIT(_rt) \