Use MNT_DETACH for lazy unmount in cleanup and delete processes to prevent "device or resource busy" errors

Author: aledbf

internal/guest/vminit/process/init.go

@@ -336,7 +336,10 @@ func (p *Init) delete(ctx context.Context) error {
 		}
 		_ = p.io.Close()
 	}
-	if err2 := mount.UnmountRecursive(p.Rootfs, 0); err2 != nil {
+	// Use MNT_DETACH for lazy unmount - this succeeds even if processes still hold
+	// references to the filesystem. The actual unmount happens when all references
+	// are released. This prevents "device or resource busy" errors during shutdown.
+	if err2 := mount.UnmountRecursive(p.Rootfs, unix.MNT_DETACH); err2 != nil {
 		log.G(ctx).WithError(err2).Warn("failed to cleanup rootfs mount")
 		if err == nil {
 			err = fmt.Errorf("failed rootfs umount: %w", err2)

internal/guest/vminit/system/cleanup.go

@@ -63,7 +63,8 @@ func cleanupBundles(ctx context.Context) {
 
 		for _, mountPath := range mounts {
 			log.G(ctx).WithField("path", mountPath).Debug("unmounting")
-			if err := mount.UnmountAll(mountPath, 0); err != nil {
+			// Use MNT_DETACH for lazy unmount - succeeds even with open file handles
+			if err := mount.UnmountAll(mountPath, unix.MNT_DETACH); err != nil {
 				log.G(ctx).WithError(err).WithField("path", mountPath).Warn("failed to unmount")
 			}
 		}