Allocate if_index before queue init

Allocate the index of a new network interface early so that the index
is available when the interface's queues are set up. This avoids
unintended concentration on net_tq(0).

Replace the kernel lock with an rwlock to serialize index map updates.
The kernel lock is not reliable here because the memory allocation
can sleep.

Also, correct the "too many interfaces" condition because the valid
index range is from 1 to USHRT_MAX.

OK bluhm@

1 files changed, 56 insertions, 10 deletions

diff --git a/sys/net/if.c b/sys/net/if.c
index 17f2265aab5..81d4efaea69 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if.c,v 1.659 2022/07/14 11:03:15 mvs Exp $	*/
+/*	$OpenBSD: if.c,v 1.660 2022/07/29 08:23:40 visa Exp $	*/
 /*	$NetBSD: if.c,v 1.35 1996/05/07 05:26:04 thorpej Exp $	*/
 
 /*
@@ -217,9 +217,12 @@ struct if_idxmap {
 	unsigned int		 serial;
 	unsigned int		 count;
 	struct srp		 map;
+	struct rwlock		 lock;
+	unsigned char		*usedidx;	/* bitmap of indices in use */
 };
 
 void	if_idxmap_init(unsigned int);
+void	if_idxmap_alloc(struct ifnet *);
 void	if_idxmap_insert(struct ifnet *);
 void	if_idxmap_remove(struct ifnet *);
 
@@ -273,7 +276,9 @@ ifinit(void)
 static struct if_idxmap if_idxmap = {
 	0,
 	0,
-	SRP_INITIALIZER()
+	SRP_INITIALIZER(),
+	RWLOCK_INITIALIZER("idxmaplk"),
+	NULL,
 };
 
 struct srp_gc if_ifp_gc = SRP_GC_INITIALIZER(if_ifp_dtor, NULL);
@@ -298,12 +303,15 @@ if_idxmap_init(unsigned int limit)
 	for (i = 0; i < limit; i++)
 		srp_init(&map[i]);
 
+	if_idxmap.usedidx = malloc(howmany(limit, NBBY),
+	    M_IFADDR, M_WAITOK | M_ZERO);
+
 	/* this is called early so there's nothing to race with */
 	srp_update_locked(&if_map_gc, &if_idxmap.map, if_map);
 }
 
 void
-if_idxmap_insert(struct ifnet *ifp)
+if_idxmap_alloc(struct ifnet *ifp)
 {
 	struct if_map *if_map;
 	struct srp *map;
@@ -311,10 +319,9 @@ if_idxmap_insert(struct ifnet *ifp)
 
 	refcnt_init(&ifp->if_refcnt);
 
-	/* the kernel lock guarantees serialised modifications to if_idxmap */
-	KERNEL_ASSERT_LOCKED();
+	rw_enter_write(&if_idxmap.lock);
 
-	if (++if_idxmap.count > USHRT_MAX)
+	if (++if_idxmap.count >= USHRT_MAX)
 		panic("too many interfaces");
 
 	if_map = srp_get_locked(&if_idxmap.map);
@@ -327,6 +334,7 @@ if_idxmap_insert(struct ifnet *ifp)
 		struct srp *nmap;
 		unsigned int nlimit;
 		struct ifnet *nifp;
+		unsigned char *nusedidx;
 
 		nlimit = if_map->limit * 2;
 		nif_map = malloc(sizeof(*nif_map) + nlimit * sizeof(*nmap),
@@ -348,6 +356,14 @@ if_idxmap_insert(struct ifnet *ifp)
 			i++;
 		}
 
+		nusedidx = malloc(howmany(nlimit, NBBY),
+		    M_IFADDR, M_WAITOK | M_ZERO);
+		memcpy(nusedidx, if_idxmap.usedidx,
+		    howmany(if_map->limit, NBBY));
+		free(if_idxmap.usedidx, M_IFADDR,
+		    howmany(if_map->limit, NBBY));
+		if_idxmap.usedidx = nusedidx;
+
 		srp_update_locked(&if_map_gc, &if_idxmap.map, nif_map);
 		if_map = nif_map;
 		map = nmap;
@@ -355,15 +371,39 @@ if_idxmap_insert(struct ifnet *ifp)
 
 	/* pick the next free index */
 	for (i = 0; i < USHRT_MAX; i++) {
-		if (index != 0 && srp_get_locked(&map[index]) == NULL)
+		if (index != 0 && isclr(if_idxmap.usedidx, index))
 			break;
 
 		index = if_idxmap.serial++ & USHRT_MAX;
 	}
+	KASSERT(index != 0 && index < if_map->limit);
+	KASSERT(isclr(if_idxmap.usedidx, index));
 
-	/* commit */
+	setbit(if_idxmap.usedidx, index);
 	ifp->if_index = index;
+
+	rw_exit_write(&if_idxmap.lock);
+}
+
+void
+if_idxmap_insert(struct ifnet *ifp)
+{
+	struct if_map *if_map;
+	struct srp *map;
+	unsigned int index = ifp->if_index;
+
+	rw_enter_write(&if_idxmap.lock);
+
+	if_map = srp_get_locked(&if_idxmap.map);
+	map = (struct srp *)(if_map + 1);
+
+	KASSERT(index != 0 && index < if_map->limit);
+	KASSERT(isset(if_idxmap.usedidx, index));
+
+	/* commit */
 	srp_update_locked(&if_ifp_gc, &map[index], if_ref(ifp));
+
+	rw_exit_write(&if_idxmap.lock);
 }
 
 void
@@ -375,8 +415,7 @@ if_idxmap_remove(struct ifnet *ifp)
 
 	index = ifp->if_index;
 
-	/* the kernel lock guarantees serialised modifications to if_idxmap */
-	KERNEL_ASSERT_LOCKED();
+	rw_enter_write(&if_idxmap.lock);
 
 	if_map = srp_get_locked(&if_idxmap.map);
 	KASSERT(index < if_map->limit);
@@ -386,7 +425,12 @@ if_idxmap_remove(struct ifnet *ifp)
 
 	srp_update_locked(&if_ifp_gc, &map[index], NULL);
 	if_idxmap.count--;
+
+	KASSERT(isset(if_idxmap.usedidx, index));
+	clrbit(if_idxmap.usedidx, index);
 	/* end of if_idxmap modifications */
+
+	rw_exit_write(&if_idxmap.lock);
 }
 
 void
@@ -607,6 +651,8 @@ if_attach_common(struct ifnet *ifp)
 		    "%s: if_qstart not set with MPSAFE set", ifp->if_xname);
 	}
 
+	if_idxmap_alloc(ifp);
+
 	ifq_init(&ifp->if_snd, ifp, 0);
 
 	ifp->if_snd.ifq_ifqs[0] = &ifp->if_snd;