From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752922AbcFNRjK (ORCPT ); Tue, 14 Jun 2016 13:39:10 -0400 Received: from foss.arm.com ([217.140.101.70]:60496 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752142AbcFNRjI (ORCPT ); Tue, 14 Jun 2016 13:39:08 -0400 Date: Tue, 14 Jun 2016 18:39:08 +0100 From: Juri Lelli To: Peter Zijlstra Cc: mingo@kernel.org, tglx@linutronix.de, rostedt@goodmis.org, xlpang@redhat.com, linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, jdesfossez@efficios.com, bristot@redhat.com Subject: Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity Message-ID: <20160614173908.GQ5981@e106622-lin> References: <20160607195635.710022345@infradead.org> <20160607200216.117270606@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160607200216.117270606@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/06/16 21:56, Peter Zijlstra wrote: > rt_mutex_waiter::prio is a copy of task_struct::prio which is updated > during the PI chain walk, such that the PI chain order isn't messed up > by (asynchronous) task state updates. > > Currently rt_mutex_waiter_less() uses task state for deadline tasks; > this is broken, since the task state can, as said above, change > asynchronously, causing the RB tree order to change without actual > tree update -> FAIL. > > Fix this by also copying the deadline into the rt_mutex_waiter state > and updating it along with its prio field. > > Ideally we would also force PI chain updates whenever DL tasks update > their deadline parameter, but for first approximation this is less > broken than it was. > The patch looks OK to me. However, I'm failing to see when we can update dl.deadline of a waiter asynchronously. Since a waiter is blocked, we can't really change his dl.deadline by calling setscheduler on him, as the update would operate on dl.dl_deadline. The new values will start to be used as soon as it gets unblocked. The situation seems different for RT tasks, for which priority change takes effect immediately. What am I missing? :-)