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 1f3540826e68..c08db9c2375d 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 fa96dfc0e1aa..7a387d237363 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,