if we get dangerously low on clusters during interrupts, we need

to free some for use on the rx rings on network cards.

this modifies m_cluncount to advise callers when we're in such a
situation, and makes them responsible for freeing up the cluster
for allocation by MCLGETI later.

fixes an awesome lockup with sis(4) henning has been experiencing.
this is not the best fix, but it is better than the current situation.

yep deraadt@ tested by henning@

1 files changed, 9 insertions, 2 deletions

diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index d0166e2e84a..ba971536e3c 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if_ethersubr.c,v 1.133 2009/06/05 00:05:21 claudio Exp $	*/
+/*	$OpenBSD: if_ethersubr.c,v 1.134 2009/08/12 14:39:05 dlg Exp $	*/
 /*	$NetBSD: if_ethersubr.c,v 1.19 1996/05/07 02:40:30 thorpej Exp $	*/
 
 /*
@@ -542,7 +542,14 @@ ether_input(ifp0, eh, m)
 	struct ether_header *eh_tmp;
 #endif
 
-	m_cluncount(m, 1);
+	/*
+	 * the cluster is no longer on the ring, so don't count it against the
+	 * ring. if the system wants the packet back we should give it back.
+	 */
+	if (m_cluncount(m) != 0) {
+		m_freem(m);
+		return;
+	}
 
 	/* mark incomming routing domain */
 	m->m_pkthdr.rdomain = ifp->if_rdomain;