On Fri, 22 Feb 2008, Gregory Haskins wrote: > Gregory Haskins wrote: > > @@ -732,14 +741,15 @@ rt_spin_lock_slowlock(struct rt_mutex *lock) > > > > debug_rt_mutex_print_deadlock(&waiter); > > > > - schedule_rt_mutex(lock); > > + update_current(TASK_UNINTERRUPTIBLE, &saved_state); > > I have a question for everyone out there about this particular part of > the code. Patch 6/14 adds an optimization that is predicated on the > order in which we modify the state==TASK_UNINTERRUPTIBLE vs reading the > waiter.task below. > > My assumption is that the xchg() (inside update_current()) acts as an > effective wmb(). If xchg() does not have this property, then this code > is broken and patch 6/14 should also add a: > > > + smp_wmb();
I believe that the wmb would be needed. I doubt that xchg on all archs would force any ordering of reads and writes. It only needs to guarantee the atomic nature of the data exchange. I don't see any reason that it would imply any type of memory barrier. -- Steve > > > > + if (waiter.task) > > + schedule_rt_mutex(lock); > > + else > > + update_current(TASK_RUNNING_MUTEX, &saved_state); > > > > spin_lock_irqsave(&lock->wait_lock, flags); > > current->flags |= saved_flags; > > current->lock_depth = saved_lock_depth; > > - state = xchg(¤t->state, TASK_UNINTERRUPTIBLE); > > - if (unlikely(state == TASK_RUNNING)) > > - saved_state = TASK_RUNNING; > > > Does anyone know the answer to this? > > Regards, > -Greg > - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
