Bug 1287399 - Allow the pre-barrier verifier to work in the presence of OMT parsing; r=jonco

--HG--
extra : rebase_source : 4983f6ef29dd4479d215169be85b481328e48784

js/src/gc/Heap.h

@@ -1304,6 +1304,9 @@ TenuredCell::readBarrier(TenuredCell* thing)
         UnmarkGrayCellRecursively(thing, thing->getTraceKind());
 }
 
+void
+AssertSafeToSkipBarrier(TenuredCell* thing);
+
 /* static */ MOZ_ALWAYS_INLINE void
 TenuredCell::writeBarrierPre(TenuredCell* thing)
 {
@@ -1312,6 +1315,22 @@ TenuredCell::writeBarrierPre(TenuredCell* thing)
     if (!thing || thing->shadowRuntimeFromAnyThread()->isHeapCollecting())
         return;
 
+#ifdef JS_GC_ZEAL
+    // When verifying pre barriers we need to switch on all barriers, even
+    // those on the Atoms Zone. Normally, we never enter a parse task when
+    // collecting in the atoms zone, so will filter out atoms below.
+    // Unfortuantely, If we try that when verifying pre-barriers, we'd never be
+    // able to handle OMT parse tasks at all as we switch on the verifier any
+    // time we're not doing GC. This would cause us to deadlock, as OMT parsing
+    // is meant to resume after GC work completes. Instead we filter out any
+    // OMT barriers that reach us and assert that they would normally not be
+    // possible.
+    if (!CurrentThreadCanAccessRuntime(thing->runtimeFromAnyThread())) {
+        AssertSafeToSkipBarrier(thing);
+        return;
+    }
+#endif
+
     JS::shadow::Zone* shadowZone = thing->shadowZoneFromAnyThread();
     if (shadowZone->needsIncrementalBarrier()) {
         MOZ_ASSERT(!RuntimeFromMainThreadIsHeapMajorCollecting(shadowZone));

js/src/gc/Verifier.cpp

@@ -286,6 +286,13 @@ CheckEdgeTracer::onChild(const JS::GCCellPtr& thing)
     }
 }
 
+void
+js::gc::AssertSafeToSkipBarrier(TenuredCell* thing)
+{
+    Zone* zone = thing->zoneFromAnyThread();
+    MOZ_ASSERT(!zone->needsIncrementalBarrier() || zone->isAtomsZone());
+}
+
 static void
 AssertMarkedOrAllocated(const EdgeValue& edge)
 {

js/src/jit-test/tests/gc/bug-1287399.js

@@ -0,0 +1,12 @@
+if (typeof gczeal != "function" || helperThreadCount() === 0)
+	quit(0);
+
+var lfGlobal = newGlobal();
+gczeal(4);
+for (lfLocal in this) {}
+lfGlobal.offThreadCompileScript(`
+  var desc = {
+    value: 'bar',
+    value: false,
+  };
+`);