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, 6 insertions, 9 deletions

diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index c543cbd62d..2c22a906da 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -7951,9 +7951,9 @@ void ClassLinker::LinkMethodsHelper<kPointerSize>::ReallocMethods(ObjPtr<mirror:
                                                                       kMethodSize,
                                                                       kMethodAlignment);
   const size_t old_methods_ptr_size = (old_methods != nullptr) ? old_size : 0;
-  auto* methods = reinterpret_cast<LengthPrefixedArray<ArtMethod>*>(
-      class_linker_->GetAllocatorForClassLoader(klass->GetClassLoader())->Realloc(
-          self_, old_methods, old_methods_ptr_size, new_size, LinearAllocKind::kArtMethodArray));
+  LinearAlloc* allocator = class_linker_->GetAllocatorForClassLoader(klass->GetClassLoader());
+  auto* methods = reinterpret_cast<LengthPrefixedArray<ArtMethod>*>(allocator->Realloc(
+      self_, old_methods, old_methods_ptr_size, new_size, LinearAllocKind::kArtMethodArray));
   CHECK(methods != nullptr);  // Native allocation failure aborts.
 
   if (methods != old_methods) {
@@ -7966,12 +7966,9 @@ void ClassLinker::LinkMethodsHelper<kPointerSize>::ReallocMethods(ObjPtr<mirror:
         ++out;
       }
     } else if (gUseUserfaultfd) {
-      // Clear the declaring class of the old dangling method array so that GC doesn't
-      // try to update them, which could cause crashes in userfaultfd GC due to
-      // checks in post-compact address computation.
-      for (auto& m : klass->GetMethods(kPointerSize)) {
-        m.SetDeclaringClass(nullptr);
-      }
+      // In order to make compaction code skip updating the declaring_class_ in
+      // old_methods, convert it into a 'no GC-root' array.
+      allocator->ConvertToNoGcRoots(old_methods, LinearAllocKind::kArtMethodArray);
     }
   }