memory: New AS helper to serialize destroy+free

If an AddressSpace has been created in its own allocated
memory, cleaning it up requires first destroying the AS
and then freeing the memory. Doing this doesn't work:

    address_space_destroy(as);
    g_free_rcu(as, rcu);

because both address_space_destroy() and g_free_rcu()
try to use the same 'rcu' node in the AddressSpace struct
and the address_space_destroy hook gets overwritten.

Provide a new address_space_destroy_free() function which
will destroy the AS and then free the memory it uses, all
in one RCU callback.

(CC to stable because the next commit needs this function.)

Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20250929144228.1994037-3-peter.maydell@linaro.org
Signed-off-by: Peter Xu <peterx@redhat.com>

include/system/memory.h

@@ -2735,11 +2735,24 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name);
  * Note that destruction of the AddressSpace is done via RCU;
  * it is therefore not valid to free the memory the AddressSpace
  * struct is in until after that RCU callback has completed.
+ * If you want to g_free() the AddressSpace after destruction you
+ * can do that with address_space_destroy_free().
  *
  * @as: address space to be destroyed
  */
 void address_space_destroy(AddressSpace *as);
 
+/**
+ * address_space_destroy_free: destroy an address space and free it
+ *
+ * This does the same thing as address_space_destroy(), and then also
+ * frees (via g_free()) the AddressSpace itself once the destruction
+ * is complete.
+ *
+ * @as: address space to be destroyed
+ */
+void address_space_destroy_free(AddressSpace *as);
+
 /**
  * address_space_remove_listeners: unregister all listeners of an address space
  *

system/memory.c

@@ -3278,7 +3278,14 @@ static void do_address_space_destroy(AddressSpace *as)
     memory_region_unref(as->root);
 }
 
-void address_space_destroy(AddressSpace *as)
+static void do_address_space_destroy_free(AddressSpace *as)
+{
+    do_address_space_destroy(as);
+    g_free(as);
+}
+
+/* Detach address space from global view, notify all listeners */
+static void address_space_detach(AddressSpace *as)
 {
     MemoryRegion *root = as->root;
 
@@ -3293,9 +3300,20 @@ void address_space_destroy(AddressSpace *as)
      * values to expire before freeing the data.
      */
     as->root = root;
+}
+
+void address_space_destroy(AddressSpace *as)
+{
+    address_space_detach(as);
     call_rcu(as, do_address_space_destroy, rcu);
 }
 
+void address_space_destroy_free(AddressSpace *as)
+{
+    address_space_detach(as);
+    call_rcu(as, do_address_space_destroy_free, rcu);
+}
+
 static const char *memory_region_type(MemoryRegion *mr)
 {
     if (mr->alias) {