Messages in this thread | | | Date | Thu, 05 Mar 2009 21:27:25 -0800 | From | Darren Hart <> | Subject | Re: [TIP][RFC 6/7] futex: add requeue_pi calls |
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Steven Rostedt wrote: > 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.
Actually no, I was talking about rt_mutex_START_proxy_lock():
/** * rt_mutex_start_proxy_lock - prepare another task to take the lock * * @lock: the rt_mutex to take * @waiter: the rt_mutex_waiter initialized by the waiter * @task: the task to prepare * @detext_deadlock: passed to task_blocks_on_rt_mutex * * The lock should have an owner, and it should not be task. * Special API call for FUTEX_REQUEUE_PI support. */ int rt_mutex_start_proxy_lock(struct rt_mutex *lock, struct rt_mutex_waiter *waiter, struct task_struct *task, int detect_deadlock) { int ret;
spin_lock(&lock->wait_lock); ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
I add the following line to fix the bug. Question is, should I use this atomic optimization here (under the lock->wait_lock) or should I just do "lock->owner |= RT_MUTEX_HAS_WAITERS" ?
=====> mark_rt_mutex_waiters(lock);
if (ret && !waiter->task) { /* * Reset the return value. We might have * returned with -EDEADLK and the owner * released the lock while we were walking the * pi chain. Let the waiter sort it out. */ ret = 0; } spin_unlock(&lock->wait_lock);
debug_rt_mutex_print_deadlock(waiter);
return ret; }
-- Darren Hart IBM Linux Technology Center Real-Time Linux Team
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