svn commit: r204409 - in releng: 7.1 7.1/sys/conf 7.1/sys/kern 7.2 7.2/sys/conf 7.2/sys/kern

[Colin Percival]

Author: cperciva
Date: Sat Feb 27 10:55:43 2010
New Revision: 204409
URL: http://svn.freebsd.org/changeset/base/204409

Log:
  MFC r197223: Fix a deadlock in the ULE scheduler.
  
  Approved by:	so (cperciva)
  Errata:		FreeBSD-EN-10:02.sched_ule

Modified:
  releng/7.1/UPDATING
  releng/7.1/sys/conf/newvers.sh
  releng/7.1/sys/kern/sched_ule.c
  releng/7.2/UPDATING
  releng/7.2/sys/conf/newvers.sh
  releng/7.2/sys/kern/sched_ule.c

Modified: releng/7.1/UPDATING
==============================================================================
--- releng/7.1/UPDATING	Sat Feb 27 10:41:30 2010	(r204408)
+++ releng/7.1/UPDATING	Sat Feb 27 10:55:43 2010	(r204409)
@@ -8,6 +8,9 @@ Items affecting the ports and packages s
 /usr/ports/UPDATING.  Please read that file before running
 portupgrade.
 
+20100227:	p11	FreeBSD-EN-10:02.sched_ule
+	Fix a deadlock in the ULE scheduler.
+
 20100106:	p10	FreeBSD-SA-10:01.bind, FreeBSD-SA-10:02.ntpd,
 			FreeBSD-SA-10:03.zfs
 	Fix BIND named(8) cache poisoning with DNSSEC validation.

Modified: releng/7.1/sys/conf/newvers.sh
==============================================================================
--- releng/7.1/sys/conf/newvers.sh	Sat Feb 27 10:41:30 2010	(r204408)
+++ releng/7.1/sys/conf/newvers.sh	Sat Feb 27 10:55:43 2010	(r204409)
@@ -32,7 +32,7 @@
 
 TYPE="FreeBSD"
 REVISION="7.1"
-BRANCH="RELEASE-p10"
+BRANCH="RELEASE-p11"
 if [ "X${BRANCH_OVERRIDE}" != "X" ]; then
 	BRANCH=${BRANCH_OVERRIDE}
 fi

Modified: releng/7.1/sys/kern/sched_ule.c
==============================================================================
--- releng/7.1/sys/kern/sched_ule.c	Sat Feb 27 10:41:30 2010	(r204408)
+++ releng/7.1/sys/kern/sched_ule.c	Sat Feb 27 10:55:43 2010	(r204409)
@@ -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

Modified: releng/7.2/UPDATING
==============================================================================
--- releng/7.2/UPDATING	Sat Feb 27 10:41:30 2010	(r204408)
+++ releng/7.2/UPDATING	Sat Feb 27 10:55:43 2010	(r204409)
@@ -8,6 +8,9 @@ Items affecting the ports and packages s
 /usr/ports/UPDATING.  Please read that file before running
 portupgrade.
 
+20100227:	p7	FreeBSD-EN-10:02.sched_ule
+	Fix a deadlock in the ULE scheduler.
+
 20100106:	p6	FreeBSD-SA-10:01.bind, FreeBSD-SA-10:02.ntpd,
 			FreeBSD-SA-10:03.zfs
 	Fix BIND named(8) cache poisoning with DNSSEC validation.

Modified: releng/7.2/sys/conf/newvers.sh
==============================================================================
--- releng/7.2/sys/conf/newvers.sh	Sat Feb 27 10:41:30 2010	(r204408)
+++ releng/7.2/sys/conf/newvers.sh	Sat Feb 27 10:55:43 2010	(r204409)
@@ -32,7 +32,7 @@
 
 TYPE="FreeBSD"
 REVISION="7.2"
-BRANCH="RELEASE-p6"
+BRANCH="RELEASE-p7"
 if [ "X${BRANCH_OVERRIDE}" != "X" ]; then
 	BRANCH=${BRANCH_OVERRIDE}
 fi

Modified: releng/7.2/sys/kern/sched_ule.c
==============================================================================
--- releng/7.2/sys/kern/sched_ule.c	Sat Feb 27 10:41:30 2010	(r204408)
+++ releng/7.2/sys/kern/sched_ule.c	Sat Feb 27 10:55:43 2010	(r204409)
@@ -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