MTX_RECURSED
if (__predict_false(v & MTX_RECURSED)) {
atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
MPASS((m->mtx_lock & (MTX_RECURSED|MTX_WAITERS)) == 0);
if (m->mtx_lock & MTX_RECURSED)
atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
#define MTX_FLAGMASK (MTX_RECURSED | MTX_WAITERS | MTX_DESTROYED)