Messages in this thread | | | Date | Thu, 5 Mar 2009 21:21:50 -0500 (EST) | From | Steven Rostedt <> | Subject | Re: [TIP][RFC 6/7] futex: add requeue_pi calls |
| |
On Thu, 5 Mar 2009, Darren Hart wrote: > > As it turns out I missed setting RT_MUTEX_HAS_WAITERS on the rt_mutex in > rt_mutex_start_proxy_lock() - seems awfully silly in retrospect - but a > little non-obvious while writing it. I added mark_rt_mutex_waiters() > after the call to task_blocks_on_rt_mutex() and the test has completed > more than 400 iterations successfully (it would fail after no more than > 2 most of the time before). > > Steven, there are several ways to set RT_MUTEX_HAS_WAITERS - but this > seemed like a reasonable approach, would you agree? Since I'm holding > the wait_lock I don't technically need the atomic cmpxchg and could > probably just set it explicity - do you have a preference? >
> + > +/** > + * rt_mutex_finish_proxy_lock - Complete the taking of the lock initialized > on > + * our behalf by another thread. > + * @lock: the rt_mutex we were woken on > + * @to: the timeout, null if none. hrtimer should already have been started. > + * @waiter: the pre-initialized rt_mutex_waiter > + * @detect_deadlock: for use by __rt_mutex_slowlock > + * > + * Special API call for PI-futex requeue support > + */ > +int rt_mutex_finish_proxy_lock(struct rt_mutex *lock, > + struct hrtimer_sleeper *to, > + struct rt_mutex_waiter *waiter, > + int detect_deadlock) > +{ > + int ret; > + > + if (waiter->task) > + schedule_rt_mutex(lock); > + > + spin_lock(&lock->wait_lock); > + > + set_current_state(TASK_INTERRUPTIBLE); > + > + ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, > + detect_deadlock); > + > + set_current_state(TASK_RUNNING); > + > + if (unlikely(waiter->task)) > + remove_waiter(lock, waiter); > + > + /* > + * try_to_take_rt_mutex() sets the waiter bit unconditionally. We > might > + * have to fix that up. > + */ > + fixup_rt_mutex_waiters(lock);
Darren,
I take it you are talking about the above.
static void fixup_rt_mutex_waiters(struct rt_mutex *lock) { if (!rt_mutex_has_waiters(lock)) clear_rt_mutex_waiters(lock); }
So it only clears the bit if there are no waiters. Yep, that should be fine. The task clearing the bit is the owner and you have the wait_lock. This should work.
-- Steve
> + > + spin_unlock(&lock->wait_lock); > + > + /* > + * Readjust priority, when we did not get the lock. We might have been > + * the pending owner and boosted. Since we did not take the lock, the > + * PI boost has to go. > + */ > + if (unlikely(ret)) > + rt_mutex_adjust_prio(current); > + > + return ret; > +}
| |