[heap] Unprotect code space lab before MakeIterable

When closing a concurrent allocator, for instance when closing a
LocalHeap, we need to make the LAB of the code space iterable.
We add then a CodePageMemoryModificationScope to allow
code space modification.

Bug: v8:12054
Change-Id: I438d7c1a50694930b7558dec2dd552bec22b7552
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3277887
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77871}

src/heap/concurrent-allocator.cc

@@ -81,10 +81,22 @@ void StressConcurrentAllocatorTask::Schedule(Isolate* isolate) {
 }
 
 void ConcurrentAllocator::FreeLinearAllocationArea() {
+  // The code page of the linear allocation area needs to be unprotected
+  // because we are going to write a filler into that memory area below.
+  base::Optional<CodePageMemoryModificationScope> optional_scope;
+  if (lab_.IsValid() && space_->identity() == CODE_SPACE) {
+    optional_scope.emplace(MemoryChunk::FromAddress(lab_.top()));
+  }
   lab_.CloseAndMakeIterable();
 }
 
 void ConcurrentAllocator::MakeLinearAllocationAreaIterable() {
+  // The code page of the linear allocation area needs to be unprotected
+  // because we are going to write a filler into that memory area below.
+  base::Optional<CodePageMemoryModificationScope> optional_scope;
+  if (lab_.IsValid() && space_->identity() == CODE_SPACE) {
+    optional_scope.emplace(MemoryChunk::FromAddress(lab_.top()));
+  }
   lab_.MakeIterable();
 }