From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751644AbaFDUI2 (ORCPT ); Wed, 4 Jun 2014 16:08:28 -0400 Received: from skprod3.natinst.com ([130.164.80.24]:41623 "EHLO ni.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750944AbaFDUI1 (ORCPT ); Wed, 4 Jun 2014 16:08:27 -0400 From: "Brad Mouring" Date: Wed, 4 Jun 2014 15:07:51 -0500 To: Thomas Gleixner Cc: Brad Mouring , Steven Rostedt , linux-rt-users , LKML , Peter Zijlstra , Ingo Molnar , Clark Williams Subject: Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes Message-ID: <20140604200750.GA10343@linuxgetsreal> 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> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-MIMETrack: Itemize by SMTP Server on US-AUS-MGWOut2/AUS/H/NIC(Release 8.5.3FP5|July 31, 2013) at 06/04/2014 03:07:52 PM, Serialize by Router on US-AUS-MGWOut2/AUS/H/NIC(Release 8.5.3FP5|July 31, 2013) at 06/04/2014 03:07:52 PM, Serialize complete at 06/04/2014 03:07:52 PM Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.12.52,1.0.14,0.0.0000 definitions=2014-06-04_04:2014-06-04,2014-06-04,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 04, 2014 at 09:53:16PM +0200, Thomas Gleixner wrote: > 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. Ah. Yeah. I haven't tested this but it seems sane to me. > > 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-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html