Messages in this thread | | | Date | Tue, 10 Jun 2014 19:41:39 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch V3 7/7] rtmutex: Avoid pointless requeueing in the deadlock detection chain walk |
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On Mon, 9 Jun 2014, Steven Rostedt wrote: > On Mon, 09 Jun 2014 20:28:10 -0000 > Thomas Gleixner <tglx@linutronix.de> wrote: > > /* > > + * If we just follow the lock chain for deadlock detection, no > > + * need to do all the requeue operations. We avoid a truckload > > s/We/To/ > > > > + * of conditinals around the various places below and just do > > s/ and/, /
Ok.
> > + * the minimum chain walk checks here. > > + */ > > + if (!requeue) { > > + /* Release the task */ > > + raw_spin_unlock_irqrestore(&task->pi_lock, flags); > > + put_task_struct(task); > > + > > + /* If there is no owner of the lock, end of chain. */ > > + if (!rt_mutex_owner(lock)) { > > + raw_spin_unlock(&lock->wait_lock); > > + return 0; > > + } > > + > > + /* Grab the next task, i.e. owner of @lock */ > > + task = rt_mutex_owner(lock); > > + get_task_struct(task); > > + raw_spin_lock_irqsave(&task->pi_lock, flags); > > + > > + /* Store whether owner is blocked itself and drop locks */ > > + next_lock = task_blocked_on(task); > > + raw_spin_unlock_irqrestore(&task->pi_lock, flags); > > + raw_spin_unlock(&lock->wait_lock); > > + > > + /* If owner is not blocked, end of chain. */ > > + if (!next_lock) > > + goto out_put_task; > > On the loop back around, have something like: > > if (top_waiter) { > if (!task_has_pi_waiters(task)) > goto out_unlock_pi;
The task has at least one pi waiter.
> if (!requeue && > top_waiter != task_top_pi_waiter(task)) { > if (!detect_deadlock) > goto out_unlock_pi; > else > requeue = false; > }
Errm? if requeue is off we are in deadlock detection chainwalk mode. So all we care about is whether task is blocked on next_lock or not.
What you actually missed is that we need to read out top_waiter for the current lock. Fixed already.
Thanks,
tglx
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