[PULL 4/6] migration: Don't do migrate cleanup if during postcopy resume

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

From: Peter Xu <peterx@redhat.com>

Below process could crash qemu with postcopy recovery:

  1. (hmp) migrate -d ..
  2. (hmp) migrate_start_postcopy
  3. [network down, postcopy paused]
  4. (hmp) migrate -r $WRONG_PORT
     when try the recover on an invalid $WRONG_PORT, cleanup_bh will be cleared
  5. (hmp) migrate -r $RIGHT_PORT
     [qemu crash on assert(cleanup_bh)]

The thing is we shouldn't cleanup if it's postcopy resume; the error is set
mostly because the channel is wrong, so we return directly waiting for the user
to retry.

migrate_fd_cleanup() should only be called when migration is cancelled or
completed.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210708190653.252961-3-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 | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/migration/migration.c b/migration/migration.c
index 38ebc6c1ab..20c48cfff1 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -3979,7 +3979,18 @@ void migrate_fd_connect(MigrationState *s, Error *error_in)
     }
     if (error_in) {
         migrate_fd_error(s, error_in);
-        migrate_fd_cleanup(s);
+        if (resume) {
+            /*
+             * Don't do cleanup for resume if channel is invalid, but only dump
+             * the error.  We wait for another channel connect from the user.
+             * The error_report still gives HMP user a hint on what failed.
+             * It's normally done in migrate_fd_cleanup(), but call it here
+             * explicitly.
+             */
+            error_report_err(error_copy(s->error));
+        } else {
+            migrate_fd_cleanup(s);
+        }
         return;
     }
 
-- 
2.31.1