Re: [PATCH] migration: NULL transport_data after freeing

[Dr. David Alan Gilbert]

* Hanna Reitz (hreitz@redhat.com) wrote:
> 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>

That probably deserves a fixes: a59136f

Reviewed-by: Dr. David Alan Gilbert <dgilbert@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
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK