[PATCH for-9.0 1/2] migration: Set migration error in migration_completion()

[Avihai Horon]

After commit 9425ef3f990a ("migration: Use migrate_has_error() in
close_return_path_on_source()"), close_return_path_on_source() assumes
that migration error is set if an error occurs during migration.

This may not be true if migration errors in migration_completion(). For
example, if qemu_savevm_state_complete_precopy() errors, migration error
will not be set.

This in turn, will cause a migration hang bug, similar to the bug that
was fixed by commit 22b04245f0d5 ("migration: Join the return path
thread before releasing to_dst_file"), as shutdown() will not be issued
for the return-path channel.

Fix it by ensuring migration error is set in case of error in
migration_completion().

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 migration/migration.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/migration/migration.c b/migration/migration.c
index 9fe8fd2afd7..b73ae3a72c4 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2799,6 +2799,7 @@ static void migration_completion(MigrationState *s)
 {
     int ret = 0;
     int current_active_state = s->state;
+    Error *local_err = NULL;
 
     if (s->state == MIGRATION_STATUS_ACTIVE) {
         ret = migration_completion_precopy(s, &current_active_state);
@@ -2832,6 +2833,15 @@ static void migration_completion(MigrationState *s)
     return;
 
 fail:
+    if (qemu_file_get_error_obj(s->to_dst_file, &local_err)) {
+        migrate_set_error(s, local_err);
+        error_free(local_err);
+    } else if (ret) {
+        error_setg_errno(&local_err, -ret, "Error in migration completion");
+        migrate_set_error(s, local_err);
+        error_free(local_err);
+    }
+
     migration_completion_failed(s, current_active_state);
 }
 
-- 
2.26.3