From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751818Ab1GWWD6 (ORCPT ); Sat, 23 Jul 2011 18:03:58 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:57533 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750978Ab1GWWDw (ORCPT ); Sat, 23 Jul 2011 18:03:52 -0400 Date: Sat, 23 Jul 2011 15:03:48 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: tglx@linutronix.de, laijs@cn.fujitsu.com, darren@dvhart.com, rostedt@goodmis.org, mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] rtmutex: Permit rt_mutex_unlock() to be invoked with irqs disabled Message-ID: <20110723220348.GD2415@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110719201410.GA10553@linux.vnet.ibm.com> <1311247968.29152.122.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1311247968.29152.122.camel@twins> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 21, 2011 at 01:32:48PM +0200, Peter Zijlstra wrote: > On Tue, 2011-07-19 at 13:14 -0700, Paul E. McKenney wrote: > > Because rcu_read_unlock() can be invoked with interrupts disabled, it can > > in turn invoke rt_mutex_unlock() with interrupts disabled. This situation > > results in lockdep splats (https://lkml.org/lkml/2011/7/7/362) because the > > rt_mutex structure's ->lock_wait is acquired elsewhere without disabling > > interrupts, which can result in deadlocks. > > > > This commit therefore changes the rt_mutex structure's ->lock_wait > > acquisitions to disable interrupts. > > > > An alternative fix is to prohibit invoking rcu_read_unlock() with > > interrupts disabled unless the entire preceding RCU read-side critical > > section has run with interrupts disabled. However, there is already > > at least one case in mainline where this potential rule is violated, > > and there might well be many more. These would likely be found one at > > a time using the lockdep-water-torture method, hence the alternative > > fix in the form of this commit. > > Thomas, I'm inclined to merge this, any objections? FWIW, it has been passing tests here. Thanx, Paul