migration/multifd: Forbid spurious wakeups

Now multifd's logic is designed to have no spurious wakeup.  I still
remember a talk to Juan and he seems to agree we should drop it now, and if
my memory was right it was there because multifd used to hit that when
still debugging.

Let's drop it and see what can explode; as long as it's not reaching
soft-freeze.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240202102857.110210-15-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/migration/multifd.c b/migration/multifd.c
index 6aa44340dec49235e20b471e71f99cab0a5f8890..28b54100cd81e04f4d8b6a522a1d2286f0002c73 100644 (file)
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -756,7 +756,9 @@ static void *multifd_send_thread(void *opaque)
             p->next_packet_size = 0;
             qatomic_set(&p->pending_job, false);
             qemu_mutex_unlock(&p->mutex);
-        } else if (qatomic_read(&p->pending_sync)) {
+        } else {
+            /* If not a normal job, must be a sync request */
+            assert(qatomic_read(&p->pending_sync));
             p->flags = MULTIFD_FLAG_SYNC;
             multifd_send_fill_packet(p);
             ret = qio_channel_write_all(p->c, (void *)p->packet,
@@ -771,9 +773,6 @@ static void *multifd_send_thread(void *opaque)
             qatomic_set(&p->pending_sync, false);
             qemu_mutex_unlock(&p->mutex);
             qemu_sem_post(&p->sem_sync);
-        } else {
-            qemu_mutex_unlock(&p->mutex);
-            /* sometimes there are spurious wakeups */
         }
     }