Do not add handler to event handlers list until ithread is created.

In rare event when fast and ithread interrupts share the same vector
and the fast handler was registered first, we can end up trying to
schedule the ithread that is not created yet. The kernel built with
INVARIANTS then triggers an assertion.

Change the order to create the ithread first and only then add the
handler that needs it to the interrupt event handlers list.

Reviewed by: jhb

1 files changed, 27 insertions, 25 deletions

diff --git a/sys/kern/kern_intr.c b/sys/kern/kern_intr.c
index a578084..8e7ac1fc 100644
--- a/sys/kern/kern_intr.c
+++ b/sys/kern/kern_intr.c
@@ -545,17 +545,6 @@ intr_event_add_handler(struct intr_event *ie, const char *name,
 		}
 	}
 
-	/* Add the new handler to the event in priority order. */
-	TAILQ_FOREACH(temp_ih, &ie->ie_handlers, ih_next) {
-		if (temp_ih->ih_pri > ih->ih_pri)
-			break;
-	}
-	if (temp_ih == NULL)
-		TAILQ_INSERT_TAIL(&ie->ie_handlers, ih, ih_next);
-	else
-		TAILQ_INSERT_BEFORE(temp_ih, ih, ih_next);
-	intr_event_update(ie);
-
 	/* Create a thread if we need one. */
 	while (ie->ie_thread == NULL && handler != NULL) {
 		if (ie->ie_flags & IE_ADDING_THREAD)
@@ -572,6 +561,18 @@ intr_event_add_handler(struct intr_event *ie, const char *name,
 			wakeup(ie);
 		}
 	}
+
+	/* Add the new handler to the event in priority order. */
+	TAILQ_FOREACH(temp_ih, &ie->ie_handlers, ih_next) {
+		if (temp_ih->ih_pri > ih->ih_pri)
+			break;
+	}
+	if (temp_ih == NULL)
+		TAILQ_INSERT_TAIL(&ie->ie_handlers, ih, ih_next);
+	else
+		TAILQ_INSERT_BEFORE(temp_ih, ih, ih_next);
+	intr_event_update(ie);
+
 	CTR3(KTR_INTR, "%s: added %s to %s", __func__, ih->ih_name,
 	    ie->ie_name);
 	mtx_unlock(&ie->ie_lock);
@@ -618,23 +619,12 @@ intr_event_add_handler(struct intr_event *ie, const char *name,
 		}
 	}
 
-	/* Add the new handler to the event in priority order. */
-	TAILQ_FOREACH(temp_ih, &ie->ie_handlers, ih_next) {
-		if (temp_ih->ih_pri > ih->ih_pri)
-			break;
-	}
-	if (temp_ih == NULL)
-		TAILQ_INSERT_TAIL(&ie->ie_handlers, ih, ih_next);
-	else
-		TAILQ_INSERT_BEFORE(temp_ih, ih, ih_next);
-	intr_event_update(ie);
-
 	/* For filtered handlers, create a private ithread to run on. */
-	if (filter != NULL && handler != NULL) { 
+	if (filter != NULL && handler != NULL) {
 		mtx_unlock(&ie->ie_lock);
-		it = ithread_create("intr: newborn", ih);		
+		it = ithread_create("intr: newborn", ih);
 		mtx_lock(&ie->ie_lock);
-		it->it_event = ie; 
+		it->it_event = ie;
 		ih->ih_thread = it;
 		ithread_update(it); /* XXX - do we really need this?!?!? */
 	} else { /* Create the global per-event thread if we need one. */
@@ -654,6 +644,18 @@ intr_event_add_handler(struct intr_event *ie, const char *name,
 			}
 		}
 	}
+
+	/* Add the new handler to the event in priority order. */
+	TAILQ_FOREACH(temp_ih, &ie->ie_handlers, ih_next) {
+		if (temp_ih->ih_pri > ih->ih_pri)
+			break;
+	}
+	if (temp_ih == NULL)
+		TAILQ_INSERT_TAIL(&ie->ie_handlers, ih, ih_next);
+	else
+		TAILQ_INSERT_BEFORE(temp_ih, ih, ih_next);
+	intr_event_update(ie);
+
 	CTR3(KTR_INTR, "%s: added %s to %s", __func__, ih->ih_name,
 	    ie->ie_name);
 	mtx_unlock(&ie->ie_lock);