OTP-8342 Processes, and/or ports could get stuck on a blocked scheduler

          when erlang:system_flag(multi_scheduling, block) was used.

          Processes, and/or ports could get stuck on an offline scheduler
          when schedulers online were reduced using
          erlang:system_flag(schedulers_online, SchedulersOnline).

2 files changed, 41 insertions, 19 deletions

diff --git a/erts/emulator/beam/erl_port_task.c b/erts/emulator/beam/erl_port_task.c
index 0fb264a53c..3cb5a966ac 100644
--- a/erts/emulator/beam/erl_port_task.c
+++ b/erts/emulator/beam/erl_port_task.c
@@ -1,19 +1,19 @@
 /*
  * %CopyrightBegin%
- * 
- * Copyright Ericsson AB 2006-2009. All Rights Reserved.
- * 
+ *
+ * Copyright Ericsson AB 2006-2010. All Rights Reserved.
+ *
  * The contents of this file are subject to the Erlang Public License,
  * Version 1.1, (the "License"); you may not use this file except in
  * compliance with the License. You should have received a copy of the
  * Erlang Public License along with this software. If not, it can be
  * retrieved online at http://www.erlang.org/.
- * 
+ *
  * Software distributed under the License is distributed on an "AS IS"
  * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
  * the License for the specific language governing rights and limitations
  * under the License.
- * 
+ *
  * %CopyrightEnd%
  */
 
@@ -902,25 +902,45 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
 
     *curr_port_pp = NULL;
 
-    if (pp->sched.taskq) {
+#ifdef ERTS_SMP
+    ASSERT(runq == (ErtsRunQueue *) erts_smp_atomic_read(&pp->run_queue));
+#endif
+
+    if (!pp->sched.taskq) {
+	ASSERT(pp->sched.exe_taskq);
+	pp->sched.exe_taskq = NULL;
+    }
+    else {
+#ifdef ERTS_SMP
+	ErtsRunQueue *xrunq;
+#endif
+
 	ASSERT(!(pp->status & ERTS_PORT_SFLGS_DEAD));
 	ASSERT(pp->sched.taskq->first);
-	enqueue_port(runq, pp);
-	port_was_enqueued = 1;
-
-	/* 
-	   erts_smp_notify_inc_runq();
 
-	 * No need to notify schedulers about the increase in run
-	 * queue length since at least this thread, which is a
-	 * scheduler, will discover that the port run queue isn't
-	 * empty before trying to go to sleep.
-	 */
+#ifdef ERTS_SMP
+	xrunq = erts_check_emigration_need(runq, ERTS_PORT_PRIO_LEVEL);
+	if (!xrunq) {
+#endif
+	    enqueue_port(runq, pp);
+	    ASSERT(pp->sched.exe_taskq);
+	    pp->sched.exe_taskq = NULL;
+	    /* No need to notify ourselves about inc in runq. */
+#ifdef ERTS_SMP
+	}
+	else {
+	    /* Port emigrated ... */
+	    erts_smp_atomic_set(&pp->run_queue, (long) xrunq);
+	    enqueue_port(xrunq, pp);
+	    ASSERT(pp->sched.exe_taskq);
+	    pp->sched.exe_taskq = NULL;
+	    erts_smp_notify_inc_runq(xrunq);
+	    erts_smp_runq_unlock(xrunq);
+	}
+#endif
+	port_was_enqueued = 1;
     }
 
-    ASSERT(pp->sched.exe_taskq);
-    pp->sched.exe_taskq = NULL;
-
     res = erts_smp_atomic_read(&erts_port_task_outstanding_io_tasks) != (long) 0;
 
     ERTS_PT_CHK_PRES_PORTQ(runq, pp);
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 5f512a9982..476e29d96f 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -5517,6 +5517,8 @@ erts_proc_migrate(Process *p, ErtsProcLocks *plcks,
     p->run_queue = to_rq;
     enqueue_process(to_rq, p);
 
+    smp_notify_inc_runq(to_rq);
+
     return ERTS_MIGRATE_SUCCESS;
 }
 #endif /* ERTS_SMP */