OTP-8612 Fix potential premature destruction of port locks

Port locks could be prematurely destroyed.

3 files changed, 31 insertions, 6 deletions

diff --git a/erts/emulator/beam/erl_port_task.c b/erts/emulator/beam/erl_port_task.c
index 0b6bb0d8e9..967a14f0d1 100644
--- a/erts/emulator/beam/erl_port_task.c
+++ b/erts/emulator/beam/erl_port_task.c
@@ -969,11 +969,11 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
     erts_port_release(pp);
 #else
     {
-	long refc = erts_smp_atomic_dectest(&pp->refc);
+	long refc;
+	erts_smp_mtx_unlock(pp->lock);
+	refc = erts_smp_atomic_dectest(&pp->refc);
 	ASSERT(refc >= 0);
-	if (refc > 0)
-	    erts_smp_mtx_unlock(pp->lock);
-	else {
+	if (refc == 0) {
 	    erts_smp_runq_unlock(runq);
 	    erts_port_cleanup(pp); /* Might aquire runq lock */
 	    erts_smp_runq_lock(runq);
diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 7c3ba69a65..d5d63631ff 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -1192,12 +1192,11 @@ erts_smp_port_unlock(Port *prt)
 {
 #ifdef ERTS_SMP
     long refc;
+    erts_smp_mtx_unlock(prt->lock);
     refc = erts_smp_atomic_dectest(&prt->refc);
     ASSERT(refc >= 0);
     if (refc == 0)
 	erts_port_cleanup(prt);
-    else
-	erts_smp_mtx_unlock(prt->lock);
 #endif
 }
 
diff --git a/erts/emulator/beam/io.c b/erts/emulator/beam/io.c
index 10f1082039..68625801cf 100644
--- a/erts/emulator/beam/io.c
+++ b/erts/emulator/beam/io.c
@@ -280,10 +280,36 @@ erts_test_next_port(int set, Uint next)
     return res;
 }
 
+
+static void port_cleanup(Port *prt);
+
+#ifdef ERTS_SMP
+
+static void
+sched_port_cleanup(void *vprt)
+{
+    Port *prt = (Port *) vprt;
+    erts_smp_mtx_lock(prt->lock);
+    port_cleanup(prt);
+}
+
+#endif
+
 void
 erts_port_cleanup(Port *prt)
 {
 #ifdef ERTS_SMP
+    if (erts_smp_mtx_trylock(prt->lock) == EBUSY)
+	erts_schedule_misc_op(sched_port_cleanup, (void *) prt);
+    else
+#endif
+	port_cleanup(prt);
+}
+
+void
+port_cleanup(Port *prt)
+{
+#ifdef ERTS_SMP
     Uint32 port_specific;
     erts_smp_mtx_t *mtx;
 #endif