[heap] Do not use always_allocate() when starting tear down

Do not use the already existing always_allocate() method for allowing
all allocations after tear down was started. Use explicit checks
of gc_state() == TEAR_DOWN instead.

This ensures that background threads extend the heap beyond its limits
only when tearing down the isolate. always_allocate() is also used
during regular execution in C++ code.

Bug: v8:10315
Change-Id: I66b5bfb06fa854048f37305a5d0cb7d60fadb30f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2390764
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69699}

src/heap/heap.cc

@@ -4920,6 +4920,10 @@ bool Heap::ShouldExpandOldGenerationOnSlowAllocation(LocalHeap* local_heap) {
   if (always_allocate() || OldGenerationSpaceAvailable() > 0) return true;
   // We reached the old generation allocation limit.
 
+  // Background threads need to be allowed to allocate without GC after teardown
+  // was initiated.
+  if (gc_state() == TEAR_DOWN) return true;
+
   // Ensure that retry of allocation on background thread succeeds
   if (IsRetryOfFailedAllocation(local_heap)) return true;
 
@@ -4944,11 +4948,6 @@ bool Heap::IsRetryOfFailedAllocation(LocalHeap* local_heap) {
   return local_heap->allocation_failed_;
 }
 
-void Heap::AlwaysAllocateAfterTearDownStarted() {
-  always_allocate_scope_count_++;
-  collection_barrier_.ShutdownRequested();
-}
-
 Heap::HeapGrowingMode Heap::CurrentHeapGrowingMode() {
   if (ShouldReduceMemory() || FLAG_stress_compaction) {
     return Heap::HeapGrowingMode::kMinimal;
@@ -5507,7 +5506,7 @@ void Heap::StartTearDown() {
   // process the event queue anymore. Avoid this deadlock by allowing all
   // allocations after tear down was requested to make sure all background
   // threads finish.
-  AlwaysAllocateAfterTearDownStarted();
+  collection_barrier_.ShutdownRequested();
 
 #ifdef VERIFY_HEAP
   // {StartTearDown} is called fairly early during Isolate teardown, so it's

src/heap/heap.h

@@ -1903,8 +1903,6 @@ class Heap {
       LocalHeap* local_heap = nullptr);
   bool IsRetryOfFailedAllocation(LocalHeap* local_heap);
 
-  void AlwaysAllocateAfterTearDownStarted();
-
   HeapGrowingMode CurrentHeapGrowingMode();
 
   double PercentToOldGenerationLimit();