migration: fix migrate_cancel multifd migration leads destination hung forever

When migrate_cancel a multifd migration, if run sequence like this:

        [source]                              [destination]

multifd_send_sync_main[finish]
                                    multifd_recv_thread wait &p->sem_sync
shutdown to_dst_file
                                    detect error from_src_file
send  RAM_SAVE_FLAG_EOS[fail]       [no chance to run multifd_recv_sync_main]
                                    multifd_load_cleanup
                                    join multifd receive thread forever

will lead destination qemu hung at following stack:

pthread_join
qemu_thread_join
multifd_load_cleanup
process_incoming_migration_co
coroutine_trampoline

Signed-off-by: Ivan Ren <ivanren@tencent.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <1561468699-9819-4-git-send-email-ivanren@tencent.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/migration/ram.c b/migration/ram.c
index eb6716710e..889148dd84 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1292,6 +1292,11 @@ int multifd_load_cleanup(Error **errp)
 
         if (p->running) {
             p->quit = true;
+            /*
+             * multifd_recv_thread may hung at MULTIFD_FLAG_SYNC handle code,
+             * however try to wakeup it without harm in cleanup phase.
+             */
+            qemu_sem_post(&p->sem_sync);
             qemu_thread_join(&p->thread);
         }
         object_unref(OBJECT(p->c));