Fix a bug in the handling of recent_activity

The problem occurred when the idle GC was turned off with +RTS -I0.
Then the scheduler would go into the state ACTIVITY_DONE_GC directly
without doing a GC, and a subsequent GC would put it back to
ACTIVITY_YES but without turning the timer back on.  Instead if the GC
finds the state is ACTIVITY_DONE_GC it should leave it there.

1 files changed, 22 insertions, 13 deletions

diff --git a/rts/Schedule.c b/rts/Schedule.c
index dee71c4676..310e68e629 100644
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -1658,21 +1658,30 @@ delete_threads_and_gc:
 
     traceSparkCounters(cap);
 
-    if (recent_activity == ACTIVITY_INACTIVE && force_major)
-    {
-        // We are doing a GC because the system has been idle for a
-        // timeslice and we need to check for deadlock.  Record the
-        // fact that we've done a GC and turn off the timer signal;
-        // it will get re-enabled if we run any threads after the GC.
-        recent_activity = ACTIVITY_DONE_GC;
-        stopTimer();
-    }
-    else
-    {
+    switch (recent_activity) {
+    case ACTIVITY_INACTIVE:
+        if (force_major) {
+            // We are doing a GC because the system has been idle for a
+            // timeslice and we need to check for deadlock.  Record the
+            // fact that we've done a GC and turn off the timer signal;
+            // it will get re-enabled if we run any threads after the GC.
+            recent_activity = ACTIVITY_DONE_GC;
+            stopTimer();
+            break;
+        }
+        // fall through...
+
+    case ACTIVITY_MAYBE_NO:
         // the GC might have taken long enough for the timer to set
-        // recent_activity = ACTIVITY_INACTIVE, but we aren't
-        // necessarily deadlocked:
+        // recent_activity = ACTIVITY_MAYBE_NO or ACTIVITY_INACTIVE,
+        // but we aren't necessarily deadlocked:
         recent_activity = ACTIVITY_YES;
+        break;
+
+    case ACTIVITY_DONE_GC:
+        // If we are actually active, the scheduler will reset the
+        // recent_activity flag and re-enable the timer.
+        break;
     }
 
 #if defined(THREADED_RTS)