Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752749AbaDRIT4 (ORCPT ); Fri, 18 Apr 2014 04:19:56 -0400 Received: from mail-ee0-f54.google.com ([74.125.83.54]:55303 "EHLO mail-ee0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752610AbaDRITd (ORCPT ); Fri, 18 Apr 2014 04:19:33 -0400 Date: Fri, 18 Apr 2014 10:19:26 +0200 From: Ingo Molnar To: Steven Rostedt Cc: LKML , linux-rt-users , Carsten Emde , Mike Galbraith , "Paul E. McKenney" , Paul Gortmaker , Thomas Gleixner , Sebastian Andrzej Siewior , Clark Williams , Frederic Weisbecker , Peter Zijlstra Subject: Re: [RFC PATCH RT V4] rwsem: The return of multi-reader PI rwsems Message-ID: <20140418081926.GC14560@gmail.com> References: <20140409151922.5fa5d999@gandalf.local.home> <20140410134217.38cd6db7@gandalf.local.home> <20140410223508.6d0fc135@gandalf.local.home> <5347E475.4020009@osadl.org> <20140411092524.1f242e25@gandalf.local.home> <20140417192603.6e379157@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140417192603.6e379157@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > Changes since v3: > > Clark reported that he was seeing a large latency when he added this > patch. I tested it out on a 8 logical CPU box, and sure enough I was > seeing it too. After spending the day debugging why, I found that I had > a bug in rt_mutex_getprio(), where I could do: > > min(task_top_pi_waiter(task)->pi_list_entry.prio, prio) > > when there was no "top_pi_waiter", which would give garbage as a > result. This would let some tasks have higher priority than they > should, and cause other tasks that should have high priority not run. Would a sanity check like the one below have helped? (untested and such) Thanks, Ingo ==========> kernel/locking/rtmutex_common.h | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h index 7431a9c..36b1ce8 100644 --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -85,6 +85,7 @@ static inline int task_has_pi_waiters(struct task_struct *p) static inline struct rt_mutex_waiter * task_top_pi_waiter(struct task_struct *p) { + WARN_ON_ONCE(!p->pi_waiters_leftmost); return rb_entry(p->pi_waiters_leftmost, struct rt_mutex_waiter, pi_tree_entry); } -- 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/