chgumtxcnt
chgumtxcnt(reg->ushm_cred->cr_ruidinfo, -1, 0);
if (!chgumtxcnt(cred->cr_ruidinfo, 1, lim_cur(td, RLIMIT_UMTXP)))
chgumtxcnt(cred->cr_ruidinfo, -1, 0);
int chgumtxcnt(struct uidinfo *uip, int diff, rlim_t maxval);