Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751321AbaL0Py2 (ORCPT ); Sat, 27 Dec 2014 10:54:28 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:24714 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750748AbaL0Py1 (ORCPT ); Sat, 27 Dec 2014 10:54:27 -0500 Message-ID: <549ED5D7.8070007@oracle.com> Date: Sat, 27 Dec 2014 10:52:55 -0500 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Davidlohr Bueso , Li Bin CC: Peter Zijlstra , Sasha Levin , Ingo Molnar , LKML , Dave Jones , rui.xiang@huawei.com, wengmeiling.weng@huawei.com Subject: Re: sched: spinlock recursion in sched_rr_get_interval References: <53B98709.3090603@oracle.com> <20140707083016.GA19379@twins.programming.kicks-ass.net> <53BAA6DF.5060409@oracle.com> <20140707200550.GA6758@twins.programming.kicks-ass.net> <549D03F6.9090607@huawei.com> <1419673927.8667.2.camel@stgolabs.net> In-Reply-To: <1419673927.8667.2.camel@stgolabs.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/27/2014 04:52 AM, Davidlohr Bueso wrote: >> Hello， >> > Does ACCESS_ONCE() can help this issue? I have no evidence that its lack is >> > responsible for the issue, but I think here need it indeed. Is that right? >> > >> > SPIN_BUG_ON(ACCESS_ONCE(lock->owner) == current, "recursion"); > Hmm I guess on a contended spinlock, there's a chance that lock->owner > can change, if the contended lock is acquired, right between the 'cond' > and spin_debug(), which would explain the bogus ->owner related > messages. Of course the same applies to ->owner_cpu. Your ACCESS_ONCE, > however, doesn't really change anything since we still read ->owner > again in spin_debug; How about something like this (untested)? There's a chance that lock->owner would change, but how would you explain it changing to 'current'? That is, what race condition specifically creates the 'lock->owner == current' situation in the debug check? Thanks, Sasha -- 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/