[PULL 5/6] migration: Clear error at entry of migrate_fd_connect()

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Peter Xu <peterx@redhat.com>

For each "migrate" command, remember to clear the s->error before going on.
For one reason, when there's a new error it'll be still remembered; see
migrate_set_error() who only sets the error if error==NULL.  Meanwhile if a
failed migration completes (e.g., postcopy recovered and finished), we
shouldn't dump an error when calling migrate_fd_cleanup() at last.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210708190653.252961-4-peterx@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/migration.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/migration/migration.c b/migration/migration.c
index 20c48cfff1..2d306582eb 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1855,6 +1855,15 @@ void migrate_set_error(MigrationState *s, const Error *error)
     }
 }
 
+static void migrate_error_free(MigrationState *s)
+{
+    QEMU_LOCK_GUARD(&s->error_mutex);
+    if (s->error) {
+        error_free(s->error);
+        s->error = NULL;
+    }
+}
+
 void migrate_fd_error(MigrationState *s, const Error *error)
 {
     trace_migrate_fd_error(error_get_pretty(error));
@@ -3970,6 +3979,13 @@ void migrate_fd_connect(MigrationState *s, Error *error_in)
     int64_t rate_limit;
     bool resume = s->state == MIGRATION_STATUS_POSTCOPY_PAUSED;
 
+    /*
+     * If there's a previous error, free it and prepare for another one.
+     * Meanwhile if migration completes successfully, there won't have an error
+     * dumped when calling migrate_fd_cleanup().
+     */
+    migrate_error_free(s);
+
     s->expected_downtime = s->parameters.downtime_limit;
     if (resume) {
         assert(s->cleanup_bh);
-- 
2.31.1