migration: Fix state transition in postcopy_start() error handling

Commit 48814111366b ("migration: Always set DEVICE state") introduced
DEVICE state to postcopy, which moved the actual state transition that
leads to POSTCOPY_ACTIVE.

However, the error handling part of the postcopy_start() function still
expects the state POSTCOPY_ACTIVE, but depending on where an error
happens, now the state can be either ACTIVE, DEVICE or CANCELLING, but
never POSTCOPY_ACTIVE, as this transition now happens just before a
successful return from the function.

Instead, accept any state except CANCELLING when transitioning to FAILED
state.

Cc: qemu-stable@nongnu.org
Fixes: 48814111366b ("migration: Always set DEVICE state")
Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20250826115145.871272-1-jmarcin@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/migration/migration.c b/migration/migration.c
index 3ff85098d5..edb8ff0d46 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2878,8 +2878,9 @@ static int postcopy_start(MigrationState *ms, Error **errp)
 fail_closefb:
     qemu_fclose(fb);
 fail:
-    migrate_set_state(&ms->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
-                          MIGRATION_STATUS_FAILED);
+    if (ms->state != MIGRATION_STATUS_CANCELLING) {
+        migrate_set_state(&ms->state, ms->state, MIGRATION_STATUS_FAILED);
+    }
     migration_block_activate(NULL);
     migration_call_notifiers(ms, MIG_EVENT_PRECOPY_FAILED, NULL);
     bql_unlock();