Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751440AbaFDTxW (ORCPT ); Wed, 4 Jun 2014 15:53:22 -0400 Received: from www.linutronix.de ([62.245.132.108]:41007 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750997AbaFDTxV (ORCPT ); Wed, 4 Jun 2014 15:53:21 -0400 Date: Wed, 4 Jun 2014 21:53:16 +0200 (CEST) From: Thomas Gleixner To: Brad Mouring cc: Steven Rostedt , linux-rt-users , LKML , Peter Zijlstra , Ingo Molnar , Clark Williams Subject: Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes In-Reply-To: <20140604192541.GA9496@linuxgetsreal> Message-ID: References: <1400855410-14773-1-git-send-email-brad.mouring@ni.com> <1400855410-14773-2-git-send-email-brad.mouring@ni.com> <20140603210609.62de6451@gandalf.local.home> <20140604114411.0fe51c1d@gandalf.local.home> <20140604192541.GA9496@linuxgetsreal> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 4 Jun 2014, Brad Mouring wrote: > On Wed, Jun 04, 2014 at 08:02:16PM +0200, Thomas Gleixner wrote: > > I'll fixup the check so it wont break the real deadlock case and queue > > it. > > How would the change break the real deadlock case? > > /* Deadlock detection */ > > if (lock == orig_lock || rt_mutex_owner(lock) == top_task) { > > + /* > > + * If the prio chain has changed out from under us, set the task > > + * to the current owner of the lock in the current waiter and > > + * continue walking the prio chain > > + */ > > + if (rt_mutex_owner(lock) && rt_mutex_owner(lock) != task) { No, sorry. That's wrong. Your change wreckages the rt_mutex_owner(lock) == top_task test simply because in that case: (rt_mutex_owner(lock) && rt_mutex_owner(lock) != task) evaluates to true. So we want this: Index: tip/kernel/locking/rtmutex.c =================================================================== --- tip.orig/kernel/locking/rtmutex.c +++ tip/kernel/locking/rtmutex.c @@ -375,6 +375,26 @@ static int rt_mutex_adjust_prio_chain(st * walk, we detected a deadlock. */ if (lock == orig_lock || rt_mutex_owner(lock) == top_task) { + /* + * If the prio chain has changed out from under us, set the task + * to the current owner of the lock in the current waiter and + * continue walking the prio chain + */ + if (rt_mutex_owner(lock) && rt_mutex_owner(lock) != task && + rt_mutex_owner(lock) != top_task) { + /* Release the old owner */ + raw_spin_unlock_irqrestore(&task->pi_lock, flags); + put_task_struct(task); + + /* Move to the new owner */ + task = rt_mutex_owner(lock); + get_task_struct(task); + + /* Let's try this again */ + raw_spin_unlock(&lock->wait_lock); + goto retry; + } + debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock); raw_spin_unlock(&lock->wait_lock); ret = deadlock_detect ? -EDEADLK : 0; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/