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Date:      Thu, 21 May 2020 11:12:28 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org
Subject:   svn commit: r361327 - stable/12/sys/kern
Message-ID:  <202005211112.04LBCSIs012346@repo.freebsd.org>
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Author: kib
Date: Thu May 21 11:12:27 2020
New Revision: 361327
URL: https://svnweb.freebsd.org/changeset/base/361327

Log:
  MFC r361037, r361056:
  Fix spurious ENOTCONN from closed unix domain socket other' side.

Modified:
  stable/12/sys/kern/uipc_socket.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/kern/uipc_socket.c
==============================================================================
--- stable/12/sys/kern/uipc_socket.c	Thu May 21 06:40:51 2020	(r361326)
+++ stable/12/sys/kern/uipc_socket.c	Thu May 21 11:12:27 2020	(r361327)
@@ -1792,8 +1792,9 @@ restart:
 				m = so->so_rcv.sb_mb;
 				goto dontblock;
 			}
-		if ((so->so_state & (SS_ISCONNECTED|SS_ISCONNECTING)) == 0 &&
-		    (so->so_proto->pr_flags & PR_CONNREQUIRED)) {
+		if ((so->so_state & (SS_ISCONNECTING | SS_ISCONNECTED |
+		    SS_ISDISCONNECTING | SS_ISDISCONNECTED)) == 0 &&
+		    (so->so_proto->pr_flags & PR_CONNREQUIRED) != 0) {
 			SOCKBUF_UNLOCK(&so->so_rcv);
 			error = ENOTCONN;
 			goto release;
@@ -3814,8 +3815,17 @@ soisdisconnected(struct socket *so)
 {
 
 	SOCK_LOCK(so);
-	so->so_state &= ~(SS_ISCONNECTING|SS_ISCONNECTED|SS_ISDISCONNECTING);
+
+	/*
+	 * There is at least one reader of so_state that does not
+	 * acquire socket lock, namely soreceive_generic().  Ensure
+	 * that it never sees all flags that track connection status
+	 * cleared, by ordering the update with a barrier semantic of
+	 * our release thread fence.
+	 */
 	so->so_state |= SS_ISDISCONNECTED;
+	atomic_thread_fence_rel();
+	so->so_state &= ~(SS_ISCONNECTING|SS_ISCONNECTED|SS_ISDISCONNECTING);
 
 	if (!SOLISTENING(so)) {
 		SOCK_UNLOCK(so);

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