On Wed, 2012-12-19 at 20:31 -0500, Steven Rostedt wrote: > > This is just an RFC patch to start discussion, not for inclusion. I may > send another patch that implements #2 above.
Signed-off-by: Steven Rostedt <[email protected]> Index: linux-rt.git/kernel/rtmutex.c =================================================================== --- linux-rt.git.orig/kernel/rtmutex.c +++ linux-rt.git/kernel/rtmutex.c @@ -167,6 +167,39 @@ static void rt_mutex_wake_waiter(struct */ int max_lock_depth = 1024; +static bool test_lock_waiter(struct task_struct *task, + struct rt_mutex_waiter *waiter, + struct rt_mutex_waiter *top_waiter, + struct rt_mutex *orig_lock, + struct rt_mutex_waiter *orig_waiter, + int detect_deadlock) +{ + /* + * Check the orig_waiter state. After we dropped the locks, + * the previous owner of the lock might have released the lock. + */ + if (orig_waiter && !rt_mutex_owner(orig_lock)) + return false; + + /* + * Drop out, when the task has no waiters. Note, + * top_waiter can be NULL, when we are in the deboosting + * mode! + */ + if (top_waiter && (!task_has_pi_waiters(task) || + top_waiter != task_top_pi_waiter(task))) + return false; + + /* + * When deadlock detection is off then we check, if further + * priority adjustment is necessary. + */ + if (!detect_deadlock && waiter->list_entry.prio == task->prio) + return false; + + return true; +} + /* * Adjust the priority chain. Also used for deadlock detection. * Decreases task's usage by one - may thus free the task. @@ -225,34 +258,32 @@ static int rt_mutex_adjust_prio_chain(st if (!rt_mutex_real_waiter(waiter)) goto out_unlock_pi; - /* - * Check the orig_waiter state. After we dropped the locks, - * the previous owner of the lock might have released the lock. - */ - if (orig_waiter && !rt_mutex_owner(orig_lock)) - goto out_unlock_pi; - - /* - * Drop out, when the task has no waiters. Note, - * top_waiter can be NULL, when we are in the deboosting - * mode! - */ - if (top_waiter && (!task_has_pi_waiters(task) || - top_waiter != task_top_pi_waiter(task))) - goto out_unlock_pi; - - /* - * When deadlock detection is off then we check, if further - * priority adjustment is necessary. - */ - if (!detect_deadlock && waiter->list_entry.prio == task->prio) + if (!test_lock_waiter(task, waiter, top_waiter, + orig_lock, orig_waiter, deadlock_detect)) goto out_unlock_pi; lock = waiter->lock; if (!raw_spin_trylock(&lock->wait_lock)) { raw_spin_unlock_irqrestore(&task->pi_lock, flags); - cpu_relax(); - goto retry; + /* + * As raw_spin_locks are FIFO, we need to avoid being + * starved out by other tasks that may be grabbing + * the wait_lock. Grab both locks in the proper + * order and test if anything changed. If it did + * we need to drop them and try again. + */ + raw_spin_lock(&lock->wait_lock); + raw_spin_lock_irqsave(&task->pi_lock, flags); + if (waiter != task->pi_blocked_on || + lock != waiter->lock || + !test_lock_waiter(task, waiter, top_waiter, + orig_lock, orig_waiter, + detect_deadlock)) { + raw_spin_unlock_irqrestore(&task->pi_lock, flags); + raw_spin_unlock(&lock->wait_lock); + cpu_relax(); + goto retry; + } } /* Deadlock detection */ -- 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/
