From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754404Ab1G0Jh2 (ORCPT ); Wed, 27 Jul 2011 05:37:28 -0400 Received: from www.linutronix.de ([62.245.132.108]:35582 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754024Ab1G0Jh1 (ORCPT ); Wed, 27 Jul 2011 05:37:27 -0400 Date: Wed, 27 Jul 2011 11:37:24 +0200 (CEST) From: Thomas Gleixner To: Darren Hart cc: Linux Kernel Mailing List , Maarten Lankhorst , Steven Rostedt Subject: Re: rt_mutex: restore wait_lock init in __rt_mutex_init In-Reply-To: <1311754711-19577-1-git-send-email-dvhart@linux.intel.com> Message-ID: References: <1311754711-19577-1-git-send-email-dvhart@linux.intel.com> User-Agent: Alpine 2.02 (LFD 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, 27 Jul 2011, Darren Hart wrote: > Without the raw_spin_lock_init(), the wait_lock does not get properly > initialized with CONFIG_DEBUG_SPINLOCK. This can manifest in a BUG() in the > futex requeue_pi path when the pi_state->pi_mutex->wait_lock fails the magic > test in rt_mutex_start_proxy_lock()->raw_spin_lock(&lock->wait_lock). That's actively wrong. You reinitialize the lock for all other cases which call this via rt_mutex_init(). There is a reason why I moved the spin lock initializer out of __rt_mutex_init() into rt_mutex_init(). The lock name stuff for lockdep ends up to be "lock->wait_lock" for all rt_mutexes, which is pretty useless when you have to analyze a lockdep splat. Thanks for finding it nevertheless. So the correct fix is: Index: linux-2.6/kernel/rtmutex.c =================================================================== --- linux-2.6.orig/kernel/rtmutex.c +++ linux-2.6/kernel/rtmutex.c @@ -1296,7 +1296,7 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init); void rt_mutex_init_proxy_locked(struct rt_mutex *lock, struct task_struct *proxy_owner) { - __rt_mutex_init(lock, NULL); + rt_mutex_init(lock); debug_rt_mutex_proxy_lock(lock, proxy_owner); rt_mutex_set_owner(lock, proxy_owner); rt_mutex_deadlock_account_lock(lock, proxy_owner);