[08/14] memory: Do not create circular reference with subregion

Commit Message

Akihiko Odaki June 26, 2024, 11:06 a.m. UTC

A memory region does not use their own reference counters, but instead
piggybacks on another QOM object, "owner" (unless the owner is not the
memory region itself). When creating a subregion, a new reference to the
owner of the container must be created. However, if the subregion is
owned by the same QOM object, this result in a self-reference, and make
the owner immortal. Avoid such a self-reference.

Signed-off-by: Akihiko Odaki <[e-mail]>
---
 system/memory.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Patch

diff --git a/system/memory.c b/system/memory.c
index 9540caa8a1f4..6645da02c658 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -2638,7 +2638,10 @@  static void memory_region_update_container_subregions(MemoryRegion *subregion)
 
     memory_region_transaction_begin();
 
-    memory_region_ref(subregion);
+    if (mr->owner != subregion->owner) {
+        memory_region_ref(subregion);
+    }
+
     QTAILQ_FOREACH(other, &mr->subregions, subregions_link) {
         if (subregion->priority >= other->priority) {
             QTAILQ_INSERT_BEFORE(other, subregion, subregions_link);
@@ -2696,7 +2699,11 @@  void memory_region_del_subregion(MemoryRegion *mr,
         assert(alias->mapped_via_alias >= 0);
     }
     QTAILQ_REMOVE(&mr->subregions, subregion, subregions_link);
-    memory_region_unref(subregion);
+
+    if (mr->owner != subregion->owner) {
+        memory_region_unref(subregion);
+    }
+
     memory_region_update_pending |= mr->enabled && subregion->enabled;
     memory_region_transaction_commit();
 }