From owner-svn-src-stable@FreeBSD.ORG  Thu Sep 24 09:08:23 2009
Return-Path: <owner-svn-src-stable@FreeBSD.ORG>
Delivered-To: svn-src-stable@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 523A8106566B;
	Thu, 24 Sep 2009 09:08:23 +0000 (UTC)
	(envelope-from attilio@FreeBSD.org)
Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c])
	by mx1.freebsd.org (Postfix) with ESMTP id 400448FC19;
	Thu, 24 Sep 2009 09:08:23 +0000 (UTC)
Received: from svn.freebsd.org (localhost [127.0.0.1])
	by svn.freebsd.org (8.14.3/8.14.3) with ESMTP id n8O98NVR091258;
	Thu, 24 Sep 2009 09:08:23 GMT (envelope-from attilio@svn.freebsd.org)
Received: (from attilio@localhost)
	by svn.freebsd.org (8.14.3/8.14.3/Submit) id n8O98Ncg091256;
	Thu, 24 Sep 2009 09:08:23 GMT (envelope-from attilio@svn.freebsd.org)
Message-Id: <200909240908.n8O98Ncg091256@svn.freebsd.org>
From: Attilio Rao <attilio@FreeBSD.org>
Date: Thu, 24 Sep 2009 09:08:23 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
	svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org
X-SVN-Group: stable-7
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Cc: 
Subject: svn commit: r197453 - in stable/7/sys: . contrib/pf kern
X-BeenThere: svn-src-stable@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: SVN commit messages for all the -stable branches of the src tree
	<svn-src-stable.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-stable>, 
	<mailto:svn-src-stable-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-stable>
List-Post: <mailto:svn-src-stable@freebsd.org>
List-Help: <mailto:svn-src-stable-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-stable>,
	<mailto:svn-src-stable-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 24 Sep 2009 09:08:23 -0000

Author: attilio
Date: Thu Sep 24 09:08:22 2009
New Revision: 197453
URL: http://svn.freebsd.org/changeset/base/197453

Log:
  MFC r197223:
  Fix a deadlock in sched_switch_migrate given by the runqueues being not
  locked at once together when doing the switch.

Modified:
  stable/7/sys/   (props changed)
  stable/7/sys/contrib/pf/   (props changed)
  stable/7/sys/kern/sched_ule.c

Modified: stable/7/sys/kern/sched_ule.c
==============================================================================
--- stable/7/sys/kern/sched_ule.c	Thu Sep 24 08:35:17 2009	(r197452)
+++ stable/7/sys/kern/sched_ule.c	Thu Sep 24 09:08:22 2009	(r197453)
@@ -1822,18 +1822,24 @@ sched_switch_migrate(struct tdq *tdq, st
 	 */
 	spinlock_enter();
 	thread_block_switch(td);	/* This releases the lock on tdq. */
-	TDQ_LOCK(tdn);
-	tdq_add(tdn, td, flags);
-	tdq_notify(td->td_sched);
-	/*
-	 * After we unlock tdn the new cpu still can't switch into this
-	 * thread until we've unblocked it in cpu_switch().  The lock
-	 * pointers may match in the case of HTT cores.  Don't unlock here
-	 * or we can deadlock when the other CPU runs the IPI handler.
+
+	/*
+	 * Acquire both run-queue locks before placing the thread on the new
+	 * run-queue to avoid deadlocks created by placing a thread with a
+	 * blocked lock on the run-queue of a remote processor.  The deadlock
+	 * occurs when a third processor attempts to lock the two queues in
+	 * question while the target processor is spinning with its own
+	 * run-queue lock held while waiting for the blocked lock to clear.
 	 */
-	if (TDQ_LOCKPTR(tdn) != TDQ_LOCKPTR(tdq)) {
-		TDQ_UNLOCK(tdn);
+	if (TDQ_LOCKPTR(tdn) == TDQ_LOCKPTR(tdq)) {
 		TDQ_LOCK(tdq);
+		tdq_add(tdn, td, flags);
+		tdq_notify(td->td_sched);
+	} else {
+		tdq_lock_pair(tdn, tdq);
+		tdq_add(tdn, td, flags);
+		tdq_notify(td->td_sched);
+		TDQ_UNLOCK(tdn);
 	}
 	spinlock_exit();
 #endif