migration/multifd: Fix multifd_send_setup cleanup when channel creation fails

When a channel fails to create, the code currently just returns. This
is wrong for two reasons:

1) Channel n+1 will not get to initialize it's semaphores, leading to
   an assert when terminate_threads tries to post to it:

 qemu-system-x86_64: ../util/qemu-thread-posix.c:92:
 qemu_mutex_lock_impl: Assertion `mutex->initialized' failed.

2) (theoretical) If channel n-1 already started creation it will
   defeat the purpose of the channels_created logic which is in place
   to avoid migrate_fd_cleanup() to run while channels are still being
   created.

   This cannot really happen today because the current failure cases
   for multifd_new_send_channel_create() are all synchronous,
   resulting from qio_channel_file_new_path() getting a bad
   filename. This would hit all channels equally.

   But I don't want to set a trap for future people, so have all
   channels try to create (even if failing), and only fail after the
   channels_created semaphore has been posted.

While here, remove the error_report_err call. There's one already at
migrate_fd_cleanup later on.

Cc: qemu-stable@nongnu.org
Reported-by: Jim Fehlig <jfehlig@suse.com>
Fixes: b7b03eb614 ("migration/multifd: Add outgoing QIOChannelFile support")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/multifd.c

@@ -1156,7 +1156,6 @@ static bool multifd_new_send_channel_create(gpointer opaque, Error **errp)
 bool multifd_send_setup(void)
 {
     MigrationState *s = migrate_get_current();
-    Error *local_err = NULL;
     int thread_count, ret = 0;
     uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
     bool use_packets = multifd_use_packets();
@@ -1177,6 +1176,7 @@ bool multifd_send_setup(void)
 
     for (i = 0; i < thread_count; i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
+        Error *local_err = NULL;
 
         qemu_sem_init(&p->sem, 0);
         qemu_sem_init(&p->sem_sync, 0);
@@ -1196,7 +1196,8 @@ bool multifd_send_setup(void)
         p->write_flags = 0;
 
         if (!multifd_new_send_channel_create(p, &local_err)) {
-            return false;
+            migrate_set_error(s, local_err);
+            ret = -1;
         }
     }
 
@@ -1209,24 +1210,27 @@ bool multifd_send_setup(void)
         qemu_sem_wait(&multifd_send_state->channels_created);
     }
 
+    if (ret) {
+        goto err;
+    }
+
     for (i = 0; i < thread_count; i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
+        Error *local_err = NULL;
 
         ret = multifd_send_state->ops->send_setup(p, &local_err);
         if (ret) {
-            break;
+            migrate_set_error(s, local_err);
+            goto err;
         }
     }
 
-    if (ret) {
-        migrate_set_error(s, local_err);
-        error_report_err(local_err);
-        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
-                          MIGRATION_STATUS_FAILED);
-        return false;
-    }
-
     return true;
+
+err:
+    migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
+                      MIGRATION_STATUS_FAILED);
+    return false;
 }
 
 bool multifd_recv(void)