Correct handling ArtMethod array during class linking

In case of userfaultfd, we were setting declaring_class_ of all
ArtMethods to nullptr. This could cause problem if a GC is taking place
simultaneously and it is visiting the ArtMethod array at the same time.

Instead, we should convert the array to a 'no gc-root array' so that
compaction code skips it. The marking-phase will simply skips it as it
will no longer be pointed by the class.

Bug: 301880194
Test: test infra
Change-Id: I72007dd94ad71aa9ccc6005eb6d99b5a8c1ad7ee

1 files changed, 7 insertions, 0 deletions

diff --git a/runtime/linear_alloc.h b/runtime/linear_alloc.h
index c40af8ad46..c81077abfc 100644
--- a/runtime/linear_alloc.h
+++ b/runtime/linear_alloc.h
@@ -56,9 +56,13 @@ class TrackingHeader final {
   bool Is16Aligned() const { return size_ & kIs16Aligned; }
 
  private:
+  void SetKind(LinearAllocKind kind) { kind_ = kind; }
+
   LinearAllocKind kind_;
   uint32_t size_;
 
+  friend class LinearAlloc;  // For SetKind()
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(TrackingHeader);
 };
 
@@ -93,6 +97,9 @@ class LinearAlloc {
   // Force arena allocator to ask for a new arena on next allocation. This
   // is to preserve private/shared clean pages across zygote fork.
   void SetupForPostZygoteFork(Thread* self) REQUIRES(!lock_);
+  // Convert the given allocated object into a `no GC-root` so that compaction
+  // skips it. Currently only used during class linking for ArtMethod array.
+  void ConvertToNoGcRoots(void* ptr, LinearAllocKind orig_kind);
 
   // Return true if the linear alloc contains an address.
   bool Contains(void* ptr) const REQUIRES(!lock_);