NFSMNT_SNDLOCK
nmp->nm_iflag |= NFSMNT_SNDLOCK;
if ((nmp->nm_iflag & NFSMNT_SNDLOCK) == 0)
nmp->nm_iflag &= ~NFSMNT_SNDLOCK;
while ((nmp->nm_iflag & NFSMNT_SNDLOCK) != 0) {