[PATCH] migration: NULL transport_data after freeing

[Hanna Reitz <hreitz@redhat.com>]

migration_incoming_state_destroy() NULLs all objects it frees after they
are freed, presumably so that a subsequent call to the same function
will not free them again, unless new objects have been created in the
meantime.

transport_data is the exception, and it shows exactly this problem: When
an incoming migration uses transport_cleanup() and transport_data, and a
subsequent incoming migration (e.g. loadvm) occurs that does not, then
when this second one is done, it will call transport_cleanup() on the
old transport_data again -- which has already been freed.  This is
sometimes visible in the iotest 201, though for some reason I can only
reproduce it with -m32.

To fix this, call transport_cleanup() only when transport_data is not
NULL (otherwise there is nothing to clean up), and set transport_data to
NULL when it has been cleaned up (i.e. freed).

(transport_cleanup() is used only by migration/socket.c, where
socket_start_incoming_migration_internal() sets both it and
transport_data to non-NULL values.)

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
---
 migration/migration.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/migration/migration.c b/migration/migration.c
index bcc385b94b..cdb2e76d02 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -287,8 +287,9 @@ void migration_incoming_state_destroy(void)
         g_array_free(mis->postcopy_remote_fds, TRUE);
         mis->postcopy_remote_fds = NULL;
     }
-    if (mis->transport_cleanup) {
+    if (mis->transport_cleanup && mis->transport_data) {
         mis->transport_cleanup(mis->transport_data);
+        mis->transport_data = NULL;
     }
 
     qemu_event_reset(&mis->main_thread_load_event);
-- 
2.34.1