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Date:      Tue, 27 Nov 2012 20:04:52 +0000 (UTC)
From:      Andre Oppermann <andre@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r243627 - head/sys/kern
Message-ID:  <201211272004.qARK4qS8047209@svn.freebsd.org>
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Author: andre
Date: Tue Nov 27 20:04:52 2012
New Revision: 243627
URL: http://svnweb.freebsd.org/changeset/base/243627

Log:
  Fix a race on listen socket teardown where while draining the
  accept queues a new socket/connection may be added to the queue
  due to a race on the ACCEPT_LOCK.
  
  The submitted patch is slightly changed in comments, teardown
  and locking order and extended with KASSERT's.
  
  Submitted by:	Vijay Singh <vijju.singh-at-gmail-dot-com>
  Found by:	His team.
  MFC after:	1 week

Modified:
  head/sys/kern/uipc_socket.c

Modified: head/sys/kern/uipc_socket.c
==============================================================================
--- head/sys/kern/uipc_socket.c	Tue Nov 27 19:35:21 2012	(r243626)
+++ head/sys/kern/uipc_socket.c	Tue Nov 27 20:04:52 2012	(r243627)
@@ -555,6 +555,16 @@ sonewconn(struct socket *head, int conns
 	so->so_snd.sb_flags |= head->so_snd.sb_flags & SB_AUTOSIZE;
 	so->so_state |= connstatus;
 	ACCEPT_LOCK();
+	/*
+	 * The accept socket may be tearing down but we just
+	 * won a race on the ACCEPT_LOCK.
+	 */
+	if (!(so->so_options & SO_ACCEPTCONN)) {
+		SOCK_LOCK(so);
+		so->so_head = NULL;
+		sofree(so);		/* NB: returns ACCEPT_UNLOCK'ed. */
+		return (NULL);
+	}
 	if (connstatus) {
 		TAILQ_INSERT_TAIL(&head->so_comp, so, so_list);
 		so->so_qstate |= SQ_COMP;
@@ -780,9 +790,14 @@ soclose(struct socket *so)
 drop:
 	if (so->so_proto->pr_usrreqs->pru_close != NULL)
 		(*so->so_proto->pr_usrreqs->pru_close)(so);
+	ACCEPT_LOCK();
 	if (so->so_options & SO_ACCEPTCONN) {
 		struct socket *sp;
-		ACCEPT_LOCK();
+		/*
+		 * Prevent new additions to the accept queues due
+		 * to ACCEPT_LOCK races while we are draining them.
+		 */
+		so->so_options &= ~SO_ACCEPTCONN;
 		while ((sp = TAILQ_FIRST(&so->so_incomp)) != NULL) {
 			TAILQ_REMOVE(&so->so_incomp, sp, so_list);
 			so->so_incqlen--;
@@ -801,13 +816,15 @@ drop:
 			soabort(sp);
 			ACCEPT_LOCK();
 		}
-		ACCEPT_UNLOCK();
+		KASSERT((TAILQ_EMPTY(&so->so_comp)),
+		    ("%s: so_comp populated", __func__));
+		KASSERT((TAILQ_EMPTY(&so->so_incomp)),
+		    ("%s: so_incomp populated", __func__));
 	}
-	ACCEPT_LOCK();
 	SOCK_LOCK(so);
 	KASSERT((so->so_state & SS_NOFDREF) == 0, ("soclose: NOFDREF"));
 	so->so_state |= SS_NOFDREF;
-	sorele(so);
+	sorele(so);			/* NB: Returns with ACCEPT_UNLOCK(). */
 	CURVNET_RESTORE();
 	return (error);
 }

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