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Date:      Wed, 25 Jan 2012 11:15:52 +0000 (UTC)
From:      Andre Oppermann <andre@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org
Subject:   svn commit: r230534 - stable/8/sys/netinet
Message-ID:  <201201251115.q0PBFqMo022466@svn.freebsd.org>
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Author: andre
Date: Wed Jan 25 11:15:52 2012
New Revision: 230534
URL: http://svn.freebsd.org/changeset/base/230534

Log:
  MFC r226113 and r228016:
   Prevent TCP sessions from stalling indefinitely in reassembly
   when reaching the zone limit of reassembly queue entries.
  
  Reviewed by:	lstewart

Modified:
  stable/8/sys/netinet/tcp_reass.c
Directory Properties:
  stable/8/sys/   (props changed)
  stable/8/sys/amd64/include/xen/   (props changed)
  stable/8/sys/cddl/contrib/opensolaris/   (props changed)
  stable/8/sys/contrib/dev/acpica/   (props changed)
  stable/8/sys/contrib/pf/   (props changed)

Modified: stable/8/sys/netinet/tcp_reass.c
==============================================================================
--- stable/8/sys/netinet/tcp_reass.c	Wed Jan 25 10:11:54 2012	(r230533)
+++ stable/8/sys/netinet/tcp_reass.c	Wed Jan 25 11:15:52 2012	(r230534)
@@ -174,7 +174,9 @@ tcp_reass(struct tcpcb *tp, struct tcphd
 	struct tseg_qent *nq;
 	struct tseg_qent *te = NULL;
 	struct socket *so = tp->t_inpcb->inp_socket;
+	char *s = NULL;
 	int flags;
+	struct tseg_qent tqs;
 
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
@@ -212,19 +214,45 @@ tcp_reass(struct tcpcb *tp, struct tcphd
 		TCPSTAT_INC(tcps_rcvmemdrop);
 		m_freem(m);
 		*tlenp = 0;
+		if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
+			log(LOG_DEBUG, "%s; %s: queue limit reached, "
+			    "segment dropped\n", s, __func__);
+			free(s, M_TCPLOG);
+		}
 		return (0);
 	}
 
 	/*
 	 * Allocate a new queue entry. If we can't, or hit the zone limit
 	 * just drop the pkt.
+	 *
+	 * Use a temporary structure on the stack for the missing segment
+	 * when the zone is exhausted. Otherwise we may get stuck.
 	 */
 	te = uma_zalloc(V_tcp_reass_zone, M_NOWAIT);
 	if (te == NULL) {
-		TCPSTAT_INC(tcps_rcvmemdrop);
-		m_freem(m);
-		*tlenp = 0;
-		return (0);
+		if (th->th_seq != tp->rcv_nxt) {
+			TCPSTAT_INC(tcps_rcvmemdrop);
+			m_freem(m);
+			*tlenp = 0;
+			if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
+			    NULL))) {
+				log(LOG_DEBUG, "%s; %s: global zone limit "
+				    "reached, segment dropped\n", s, __func__);
+				free(s, M_TCPLOG);
+			}
+			return (0);
+		} else {
+			bzero(&tqs, sizeof(struct tseg_qent));
+			te = &tqs;
+			if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
+			    NULL))) {
+				log(LOG_DEBUG,
+				    "%s; %s: global zone limit reached, using "
+				    "stack for missing segment\n", s, __func__);
+				free(s, M_TCPLOG);
+			}
+		}
 	}
 	tp->t_segqlen++;
 
@@ -301,6 +329,8 @@ tcp_reass(struct tcpcb *tp, struct tcphd
 	if (p == NULL) {
 		LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
 	} else {
+		KASSERT(te != &tqs, ("%s: temporary stack based entry not "
+		    "first element in queue", __func__));
 		LIST_INSERT_AFTER(p, te, tqe_q);
 	}
 
@@ -324,7 +354,8 @@ present:
 			m_freem(q->tqe_m);
 		else
 			sbappendstream_locked(&so->so_rcv, q->tqe_m);
-		uma_zfree(V_tcp_reass_zone, q);
+		if (q != &tqs)
+			uma_zfree(V_tcp_reass_zone, q);
 		tp->t_segqlen--;
 		q = nq;
 	} while (q && q->tqe_th->th_seq == tp->rcv_nxt);

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