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Date: Wed, 15 Jun 2016 19:55:12 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: mingo@...nel.org, tglx@...utronix.de, juri.lelli@....com, xlpang@...hat.com, linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com, jdesfossez@...icios.com, bristot@...hat.com, Ingo Molnar <mingo@...hat.com> Subject: Re: [RFC][PATCH 3/8] sched/deadline/rtmutex: Dont miss the dl_runtime/dl_period update On Wed, Jun 15, 2016 at 12:30:07PM -0400, Steven Rostedt wrote: > > +++ b/kernel/locking/rtmutex.c > > @@ -488,7 +488,7 @@ static int rt_mutex_adjust_prio_chain(st > > * enabled we continue, but stop the requeueing in the chain > > * walk. > > */ > > - if (waiter->prio == task->prio) { > > + if (waiter->prio == task->prio && !dl_task(task)) { > > Isn't task the owner of the lock? No, task is blocked on something. > What happens if the waiter is a > deadline task? So the test here is a shortcut to terminate the Pi chain adjust, it says that if the waiter and task have the same priority, we're done. Further adjustments will not make a difference. The problem is that for deadline tasks, prio is a useless number, so even if they match (all deadline tasks have prio -1) they might still not actually match. After the last patch I suppose we could do something like: waiter->prio == task->prio && waiter->deadline == task->dl.deadline In any case, any condition that compares just two 'prio' values is per definition broken if DL tasks are involved.
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