static int coroutine_fn put_fid(V9fsPDU *pdu, V9fsFidState *fidp)
{
    BUG_ON(!fidp->ref);
    fidp->ref--;
    /*
     * Don't free the fid if it is in reclaim list
     */
    if (!fidp->ref && fidp->clunked) {
        if (fidp->fid == pdu->s->root_fid) {
            /*
             * if the clunked fid is root fid then we
             * have unmounted the fs on the client side.
             * delete the migration blocker. Ideally, this
             * should be hooked to transport close notification
             */
            if (pdu->s->migration_blocker) {
                migrate_del_blocker(pdu->s->migration_blocker);
                error_free(pdu->s->migration_blocker);
                pdu->s->migration_blocker = NULL;
            }
        }
        return free_fid(pdu, fidp);
    }
    return 0;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.