Re: [PATCH v1 1/1] migration: Unregister yank if migration setup fails

[Dr. David Alan Gilbert]

* Leonardo Bras (leobras@redhat.com) wrote:
> Currently, if a qemu instance is started with "-incoming defer" and
> an incorect parameter is passed to "migrate_incoming", it will print the
> expected error and reply with "duplicate yank instance" for any upcoming
> "migrate_incoming" command.
> 
> This renders current qemu process unusable, and requires a new qemu
> process to be started before accepting a migration.
> 
> This is caused by a yank_register_instance() that happens in
> qemu_start_incoming_migration() but is never reverted if any error
> happens.
> 
> Solves this by unregistering the instance if anything goes wrong
> in the function, allowing a new "migrate_incoming" command to be
> accepted.
> 
> Fixes: b5eea99ec2f ("migration: Add yank feature", 2021-01-13)
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1974366
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> 
> ---
>  migration/migration.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 4228635d18..ddcf9e1868 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -474,9 +474,13 @@ 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);
>      }
> +
> +    if (*errp) {
> +        yank_unregister_instance(MIGRATION_YANK_INSTANCE);
> +    }

My understanding is that testing *errp isn't allowed, because
it's legal to pass NULL to ignore errors, or legal to pass
&error_abort to mean that any error you do hit will cause the
process to assert; so you need to have something separate you can test.

Dave

>  }
>  
>  static void process_incoming_migration_bh(void *opaque)
> -- 
> 2.32.0
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK