2 files changed, 53 insertions, 26 deletions

diff --git a/arch/ia64/sn/kernel/xpc_channel.c b/arch/ia64/sn/kernel/xpc_channel.c
index 1f3540826e6..c08db9c2375 100644
--- a/arch/ia64/sn/kernel/xpc_channel.c
+++ b/arch/ia64/sn/kernel/xpc_channel.c
@@ -632,7 +632,7 @@ xpc_process_connect(struct xpc_channel *ch, unsigned long *irq_flags)
 		ch->number, ch->partid);
 
 	spin_unlock_irqrestore(&ch->lock, *irq_flags);
-	xpc_create_kthreads(ch, 1);
+	xpc_create_kthreads(ch, 1, 0);
 	spin_lock_irqsave(&ch->lock, *irq_flags);
 }
 
@@ -754,12 +754,12 @@ xpc_process_disconnect(struct xpc_channel *ch, unsigned long *irq_flags)
 
 	/* make sure all activity has settled down first */
 
-	if (atomic_read(&ch->references) > 0 ||
-			((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
-			!(ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE))) {
+	if (atomic_read(&ch->kthreads_assigned) > 0 ||
+				atomic_read(&ch->references) > 0) {
 		return;
 	}
-	DBUG_ON(atomic_read(&ch->kthreads_assigned) != 0);
+	DBUG_ON((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+			!(ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE));
 
 	if (part->act_state == XPC_P_DEACTIVATING) {
 		/* can't proceed until the other side disengages from us */
@@ -1651,6 +1651,11 @@ xpc_disconnect_channel(const int line, struct xpc_channel *ch,
 	/* wake all idle kthreads so they can exit */
 	if (atomic_read(&ch->kthreads_idle) > 0) {
 		wake_up_all(&ch->idle_wq);
+
+	} else if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+			!(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
+		/* start a kthread that will do the xpcDisconnecting callout */
+		xpc_create_kthreads(ch, 1, 1);
 	}
 
 	/* wake those waiting to allocate an entry from the local msg queue */
diff --git a/arch/ia64/sn/kernel/xpc_main.c b/arch/ia64/sn/kernel/xpc_main.c
index fa96dfc0e1a..7a387d23736 100644
--- a/arch/ia64/sn/kernel/xpc_main.c
+++ b/arch/ia64/sn/kernel/xpc_main.c
@@ -681,7 +681,7 @@ xpc_activate_kthreads(struct xpc_channel *ch, int needed)
 	dev_dbg(xpc_chan, "create %d new kthreads, partid=%d, channel=%d\n",
 		needed, ch->partid, ch->number);
 
-	xpc_create_kthreads(ch, needed);
+	xpc_create_kthreads(ch, needed, 0);
 }
 
 
@@ -775,26 +775,28 @@ xpc_daemonize_kthread(void *args)
 		xpc_kthread_waitmsgs(part, ch);
 	}
 
-	if (atomic_dec_return(&ch->kthreads_assigned) == 0) {
-		spin_lock_irqsave(&ch->lock, irq_flags);
-		if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
-				!(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
-			ch->flags |= XPC_C_DISCONNECTINGCALLOUT;
-			spin_unlock_irqrestore(&ch->lock, irq_flags);
+	/* let registerer know that connection is disconnecting */
 
-			xpc_disconnect_callout(ch, xpcDisconnecting);
-
-			spin_lock_irqsave(&ch->lock, irq_flags);
-			ch->flags |= XPC_C_DISCONNECTINGCALLOUT_MADE;
-		}
+	spin_lock_irqsave(&ch->lock, irq_flags);
+	if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+			!(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
+		ch->flags |= XPC_C_DISCONNECTINGCALLOUT;
 		spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+		xpc_disconnect_callout(ch, xpcDisconnecting);
+
+		spin_lock_irqsave(&ch->lock, irq_flags);
+		ch->flags |= XPC_C_DISCONNECTINGCALLOUT_MADE;
+	}
+	spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+	if (atomic_dec_return(&ch->kthreads_assigned) == 0) {
 		if (atomic_dec_return(&part->nchannels_engaged) == 0) {
 			xpc_mark_partition_disengaged(part);
 			xpc_IPI_send_disengage(part);
 		}
 	}
 
-
 	xpc_msgqueue_deref(ch);
 
 	dev_dbg(xpc_chan, "kthread exiting, partid=%d, channel=%d\n",
@@ -818,7 +820,8 @@ xpc_daemonize_kthread(void *args)
  * partition.
  */
 void
-xpc_create_kthreads(struct xpc_channel *ch, int needed)
+xpc_create_kthreads(struct xpc_channel *ch, int needed,
+			int ignore_disconnecting)
 {
 	unsigned long irq_flags;
 	pid_t pid;
@@ -833,16 +836,38 @@ xpc_create_kthreads(struct xpc_channel *ch, int needed)
 		 * kthread. That kthread is responsible for doing the
 		 * counterpart to the following before it exits.
 		 */
+		if (ignore_disconnecting) {
+			if (!atomic_inc_not_zero(&ch->kthreads_assigned)) {
+				/* kthreads assigned had gone to zero */
+				BUG_ON(!(ch->flags &
+					XPC_C_DISCONNECTINGCALLOUT_MADE));
+				break;
+			}
+
+		} else if (ch->flags & XPC_C_DISCONNECTING) {
+			break;
+
+		} else if (atomic_inc_return(&ch->kthreads_assigned) == 1) {
+			if (atomic_inc_return(&part->nchannels_engaged) == 1)
+				xpc_mark_partition_engaged(part);
+		}
 		(void) xpc_part_ref(part);
 		xpc_msgqueue_ref(ch);
-		if (atomic_inc_return(&ch->kthreads_assigned) == 1 &&
-		    atomic_inc_return(&part->nchannels_engaged) == 1) {
-			xpc_mark_partition_engaged(part);
-		}
 
 		pid = kernel_thread(xpc_daemonize_kthread, (void *) args, 0);
 		if (pid < 0) {
 			/* the fork failed */
+
+			/*
+			 * NOTE: if (ignore_disconnecting &&
+			 * !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) is true,
+			 * then we'll deadlock if all other kthreads assigned
+			 * to this channel are blocked in the channel's
+			 * registerer, because the only thing that will unblock
+			 * them is the xpcDisconnecting callout that this
+			 * failed kernel_thread would have made.
+			 */
+
 			if (atomic_dec_return(&ch->kthreads_assigned) == 0 &&
 			    atomic_dec_return(&part->nchannels_engaged) == 0) {
 				xpc_mark_partition_disengaged(part);
@@ -857,9 +882,6 @@ xpc_create_kthreads(struct xpc_channel *ch, int needed)
 				 * Flag this as an error only if we have an
 				 * insufficient #of kthreads for the channel
 				 * to function.
-				 *
-				 * No xpc_msgqueue_ref() is needed here since
-				 * the channel mgr is doing this.
 				 */
 				spin_lock_irqsave(&ch->lock, irq_flags);
 				XPC_DISCONNECT_CHANNEL(ch, xpcLackOfResources,