[Qemu-devel] [PATCH 1/3] memory: allow destroying a non-empty MemoryRegion

[Paolo Bonzini <pbonzini@redhat.com>]

This is legal; the MemoryRegion will simply unreference all the
existing subregions and possibly bring them down with it as well.
However, it requires a bit of care to avoid an infinite loop.
Finalizing a memory region cannot trigger an address space update,
but memory_region_del_subregion errs on the side of caution and
might trigger a spurious update: avoid that by resetting mr->enabled
first.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 memory.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/memory.c b/memory.c
index ef87363..73d28ba 100644
--- a/memory.c
+++ b/memory.c
@@ -1304,7 +1304,22 @@ static void memory_region_finalize(Object *obj)
 {
     MemoryRegion *mr = MEMORY_REGION(obj);
 
-    assert(QTAILQ_EMPTY(&mr->subregions));
+    assert(!mr->container);
+
+    /* We know the region is not visible in any address space (it
+     * does not have a container and cannot be a root either because
+     * it has no references, so we can blindly clear mr->enabled.
+     * memory_region_set_enabled instead could trigger a transaction
+     * and cause an infinite loop.
+     */
+    mr->enabled = false;
+    memory_region_transaction_begin();
+    while (!QTAILQ_EMPTY(&mr->subregions)) {
+        MemoryRegion *subregion = QTAILQ_FIRST(&mr->subregions);
+        memory_region_del_subregion(mr, subregion);
+    }
+    memory_region_transaction_commit();
+
     mr->destructor(mr);
     memory_region_clear_coalescing(mr);
     g_free((char *)mr->name);
-- 
2.5.0