On Mon, 10 Feb 2014 18:17:12 +0100 Nicholas Mc Guire <[email protected]> wrote:
> > > > In rtmutex.c we have: > > > > pi_lock(&self->pi_lock); > > __set_current_state(self->saved_state); > > self->saved_state = TASK_RUNNING; > > pi_unlock(&self->pi_lock); > > > > As there is no wmb() here, it can be very possible that another CPU > > will see saved_state as TASK_RUNNING, and current state as > > TASK_RUNNING, and miss the update completely. > > > > I would not want to add a wmb() unless there is a real bug with the > > check state, as the above is in a very fast path and the check state is > > in a slower path. > > > maybe I'm missing/missunderstanding something here but > pi_unlock -> arch_spin_unlock is a full mb() > so once any task did an update of the state the loop should be catching > this update ? if the loop exits before the updat takes effect (pi_unlock) > would that be ncorrect ? Even if the spin locks were full memory barriers, it is still buggy. The fact that we set current_state to saved_state, and then saved_state to TASK_RUNNING without any memory barriers in between those two statements, means that the reader (even with a rmb()) can still see both as TASK_RUNNING. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
