Re: [PATCH 1/2] migration: Move yank outside qemu_start_incoming_migration()

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> Starting from commit b5eea99ec2f5c, qmp_migrate_recover() calls unregister
> before calling qemu_start_incoming_migration(). I believe it wanted to mitigate
> the next call to yank_register_instance(), but I think that's wrong.
> 
> Firstly, if during recover, we should keep the yank instance there, not
> "quickly removing and adding it back".
> 
> Meanwhile, calling qmp_migrate_recover() twice with b5eea99ec2f5c will directly
> crash the dest qemu (right now it can't; but it'll start to work right after
> the next patch) because the 1st call of qmp_migrate_recover() will unregister
> permanently when the channel failed to establish, then the 2nd call of
> qmp_migrate_recover() crashes at yank_unregister_instance().
> 
> This patch fixes it by moving yank ops out of qemu_start_incoming_migration()
> into qmp_migrate_incoming.  For qmp_migrate_recover(), drop the unregister of
> yank instance too since we keep it there during the recovery phase.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/migration.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 4228635d18..1bb03d1eca 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -456,10 +456,6 @@ static void qemu_start_incoming_migration(const char *uri, Error **errp)
>  {
>      const char *p = NULL;
>  
> -    if (!yank_register_instance(MIGRATION_YANK_INSTANCE, errp)) {
> -        return;
> -    }
> -
>      qapi_event_send_migration(MIGRATION_STATUS_SETUP);
>      if (strstart(uri, "tcp:", &p) ||
>          strstart(uri, "unix:", NULL) ||
> @@ -474,7 +470,6 @@ static void qemu_start_incoming_migration(const char *uri, Error **errp)
>      } else if (strstart(uri, "fd:", &p)) {
>          fd_start_incoming_migration(p, errp);
>      } else {
> -        yank_unregister_instance(MIGRATION_YANK_INSTANCE);
>          error_setg(errp, "unknown migration protocol: %s", uri);
>      }
>  }
> @@ -2083,9 +2078,14 @@ void qmp_migrate_incoming(const char *uri, Error **errp)
>          return;
>      }
>  
> +    if (!yank_register_instance(MIGRATION_YANK_INSTANCE, errp)) {
> +        return;
> +    }
> +
>      qemu_start_incoming_migration(uri, &local_err);
>  
>      if (local_err) {
> +        yank_unregister_instance(MIGRATION_YANK_INSTANCE);
>          error_propagate(errp, local_err);
>          return;
>      }
> @@ -2114,7 +2114,6 @@ void qmp_migrate_recover(const char *uri, Error **errp)
>       * only re-setup the migration stream and poke existing migration
>       * to continue using that newly established channel.
>       */
> -    yank_unregister_instance(MIGRATION_YANK_INSTANCE);
>      qemu_start_incoming_migration(uri, errp);
>  }
>  
> -- 
> 2.31.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK