Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751544AbaAPGqZ (ORCPT ); Thu, 16 Jan 2014 01:46:25 -0500 Received: from g4t0017.houston.hp.com ([15.201.24.20]:4508 "EHLO g4t0017.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbaAPGqX (ORCPT ); Thu, 16 Jan 2014 01:46:23 -0500 Message-ID: <1389854777.2126.20.camel@j-VirtualBox> Subject: Re: [RFC 3/3] mutex: When there is no owner, stop spinning after too many tries From: Jason Low To: Linus Torvalds Cc: Ingo Molnar , Peter Zijlstra , Paul McKenney , Waiman Long , Thomas Gleixner , Linux Kernel Mailing List , Rik van Riel , Andrew Morton , Davidlohr Bueso , Peter Anvin , "Chandramouleeswaran, Aswin" , "Norton, Scott J" Date: Wed, 15 Jan 2014 22:46:17 -0800 In-Reply-To: References: <1389745990-7069-1-git-send-email-jason.low2@hp.com> <1389745990-7069-4-git-send-email-jason.low2@hp.com> <1389840330.2944.104.camel@j-VirtualBox> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-01-16 at 10:14 +0700, Linus Torvalds wrote: > On Thu, Jan 16, 2014 at 9:45 AM, Jason Low wrote: > > > > Any comments on the below change which unlocks the mutex before taking > > the lock->wait_lock to wake up a waiter? Thanks. > > Hmm. Doesn't that mean that a new lock owner can come in *before* > you've called debug_mutex_unlock and the lockdep stuff, and get the > lock? And then debug_mutex_lock() will be called *before* the unlocker > called debug_mutex_unlock(), which I'm sure confuses things. If obtaining the wait_lock for debug_mutex_unlock is the issue, then perhaps we can address that by taking care of #ifdef CONFIG_DEBUG_MUTEXES. In the CONFIG_DEBUG_MUTEXES case, we can take the wait_lock first, and in the regular case, take the wait_lock after releasing the mutex. #ifdef CONFIG_DEBUG_MUTEXES spin_lock_mutex(&lock->wait_lock, flags); #endif mutex_release(&lock->dep_map, nested, _RET_IP_); debug_mutex_unlock(lock); if (__mutex_slowpath_needs_to_unlock()) atomic_set(&lock->count, 1); #ifndef CONFIG_DEBUG_MUTEXES spin_lock_mutex(&lock->wait_lock, flags); #endif -- 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/