Use mutex_owned(9F) to Validate and Document Locking Requirements

int mutex_owned(kmutex_t *mp);

A significant portion of driver development involves properly handling multiple threads. Comments should always be used when a mutex is acquired; they are even more useful when an apparently necessary mutex is not acquired. To determine if a mutex is held by a thread, use mutex_owned(9F) within ASSERT(9F):

void helper(void)
{
        /* this routine should always be called with xsp's mutex held */
        ASSERT(mutex_owned(&xsp->mu));
        ...
}

mutex_owned(9F) is only valid within ASSERT(9F) macros. Under no circumstances should you use it to control the behavior of a driver.