From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934027AbcI2OwN (ORCPT ); Thu, 29 Sep 2016 10:52:13 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:55744 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933286AbcI2OwF (ORCPT ); Thu, 29 Sep 2016 10:52:05 -0400 Date: Thu, 29 Sep 2016 10:49:27 -0400 (EDT) From: Thomas Gleixner To: Peter Zijlstra cc: mingo@kernel.org, juri.lelli@arm.com, rostedt@goodmis.org, xlpang@redhat.com, bigeasy@linutronix.de, linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, jdesfossez@efficios.com, bristot@redhat.com, Ingo Molnar Subject: Re: [PATCH -v2 2/9] sched/rtmutex/deadline: Fix a PI crash for deadline tasks In-Reply-To: <20160926124127.932737914@infradead.org> Message-ID: References: <20160926123213.851818224@infradead.org> <20160926124127.932737914@infradead.org> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 26 Sep 2016, Peter Zijlstra wrote: > This is because rt_mutex_enqueue_pi() and rt_mutex_dequeue_pi() > are only protected by pi_lock when operating pi waiters, while > rt_mutex_get_top_task(), will access them with rq lock held but > not holding pi_lock. > > In order to tackle it, we introduce new "pi_top_task" pointer > cached in task_struct, and add new rt_mutex_update_top_task() > to update its value, it can be called by rt_mutex_setprio() > which held both owner's pi_lock and rq lock. Thus "pi_top_task" > can be safely accessed by enqueue_task_dl() under rq lock. Reviewed-by: Thomas Gleixner