From 8f6fcd8e8de8ac332577f4cc44af1c9cb8b0b065 Mon Sep 17 00:00:00 2001
From: Kunal Sareen <kunal.sareen@anu.edu.au>
Date: Thu, 18 Jul 2024 04:18:05 +0000
Subject: [PATCH] Fix stale unlog bits for LOS and MarkSweepSpace objects

We now:
 - Clear the unlog bits for dead LOS objects
 - Bulk clear the unlog bits for MarkSweepSpace for full heap GC
 - Set the unlog bits for LOS and MarkSweepSpace objects during trace
   object

This is because we want to ensure the unlog bits are only set for
objects that are alive. We do not reset the unlogs bits inside the
`ProcessModBuf` work packet because we do not know what objects are
alive at that moment in time.
---
 src/policy/largeobjectspace.rs                |  8 +++++++-
 src/policy/marksweepspace/native_ms/global.rs | 14 ++++++++++++--
 src/util/metadata/log_bit.rs                  |  5 +++++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/policy/largeobjectspace.rs b/src/policy/largeobjectspace.rs
index 64a13c8f37..f5305d0a09 100644
--- a/src/policy/largeobjectspace.rs
+++ b/src/policy/largeobjectspace.rs
@@ -209,7 +209,9 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
                 trace!("LOS object {} is being marked now", object);
                 self.treadmill.copy(object, nursery_object);
                 // We just moved the object out of the logical nursery, mark it as unlogged.
-                if nursery_object && self.common.needs_log_bit {
+                // We also set the unlog bit for mature objects to ensure that
+                // any modifications to them are logged
+                if self.common.needs_log_bit {
                     VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC
                         .mark_as_unlogged::<VM>(object, Ordering::SeqCst);
                 }
@@ -228,6 +230,10 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
         let sweep = |object: ObjectReference| {
             #[cfg(feature = "vo_bit")]
             crate::util::metadata::vo_bit::unset_vo_bit::<VM>(object);
+            if self.common.needs_log_bit {
+                VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC
+                    .clear::<VM>(object, Ordering::SeqCst);
+            }
             self.pr
                 .release_pages(get_super_page(object.to_object_start::<VM>()));
         };
diff --git a/src/policy/marksweepspace/native_ms/global.rs b/src/policy/marksweepspace/native_ms/global.rs
index 81cc10fdf5..7db92cf73c 100644
--- a/src/policy/marksweepspace/native_ms/global.rs
+++ b/src/policy/marksweepspace/native_ms/global.rs
@@ -321,7 +321,7 @@ impl<VM: VMBinding> MarkSweepSpace<VM> {
                 block.set_state(BlockState::Marked);
                 queue.enqueue(object);
                 if self.common.needs_log_bit {
-                    VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC.mark_as_unlogged::<VM>(object, Ordering::SeqCst);
+                    VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC.mark_byte_as_unlogged::<VM>(object, Ordering::SeqCst);
                 }
             }
             object
@@ -337,7 +337,7 @@ impl<VM: VMBinding> MarkSweepSpace<VM> {
         Block::NEXT_BLOCK_TABLE
     }
 
-    pub fn prepare(&mut self, _full_heap: bool) {
+    pub fn prepare(&mut self, full_heap: bool) {
         if let MetadataSpec::OnSide(side) = *VM::VMObjectModel::LOCAL_MARK_BIT_SPEC {
             for chunk in self.chunk_map.all_chunks() {
                 side.bzero_metadata(chunk.start(), Chunk::BYTES);
@@ -345,6 +345,16 @@ impl<VM: VMBinding> MarkSweepSpace<VM> {
         } else {
             unimplemented!("in header mark bit is not supported");
         }
+
+        if self.common.needs_log_bit && full_heap {
+            if let MetadataSpec::OnSide(side) = *VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC {
+                for chunk in self.chunk_map.all_chunks() {
+                    side.bzero_metadata(chunk.start(), Chunk::BYTES);
+                }
+            } else {
+                unimplemented!("in header log bit is not supported");
+            }
+        }
     }
 
     pub fn release(&mut self) {
diff --git a/src/util/metadata/log_bit.rs b/src/util/metadata/log_bit.rs
index 6b387041fb..d29ca6ebf2 100644
--- a/src/util/metadata/log_bit.rs
+++ b/src/util/metadata/log_bit.rs
@@ -6,6 +6,11 @@ use std::sync::atomic::Ordering;
 use super::MetadataSpec;
 
 impl VMGlobalLogBitSpec {
+    /// Clear the unlog bit to log object (0 means logged)
+    pub fn clear<VM: VMBinding>(&self, object: ObjectReference, order: Ordering) {
+        self.store_atomic::<VM, u8>(object, 0, None, order)
+    }
+
     /// Mark the log bit as unlogged (1 means unlogged)
     pub fn mark_as_unlogged<VM: VMBinding>(&self, object: ObjectReference, order: Ordering) {
         self.store_atomic::<VM, u8>(object, 1, None, order)