On Mon, 10 Feb 2014, Steven Rostedt wrote: > On Mon, 10 Feb 2014 18:17:12 +0100 > Nicholas Mc Guire <der.herr@xxxxxxx> 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. > ok - thanks - I think now I got it. thx! hofrat -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
