From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752208AbdF3Mue (ORCPT ); Fri, 30 Jun 2017 08:50:34 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52492 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751796AbdF3Mub (ORCPT ); Fri, 30 Jun 2017 08:50:31 -0400 Date: Fri, 30 Jun 2017 05:50:20 -0700 From: "Paul E. McKenney" To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net, manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de, linux-arch@vger.kernel.org, will.deacon@arm.com, peterz@infradead.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, torvalds@linux-foundation.org Subject: Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with lock/unlock pair Reply-To: paulmck@linux.vnet.ibm.com References: <20170629235918.GA6445@linux.vnet.ibm.com> <1498780894-8253-2-git-send-email-paulmck@linux.vnet.ibm.com> <20170630110445.GA5123@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170630110445.GA5123@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17063012-0036-0000-0000-0000023C7CAD X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007297; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00880861; UDB=6.00439163; IPR=6.00661014; BA=6.00005448; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016023; XFM=3.00000015; UTC=2017-06-30 12:50:25 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17063012-0037-0000-0000-000040ECFF52 Message-Id: <20170630125020.GU2393@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-06-30_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1706300204 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 30, 2017 at 01:04:45PM +0200, Oleg Nesterov wrote: > On 06/29, Paul E. McKenney wrote: > > > > --- a/kernel/task_work.c > > +++ b/kernel/task_work.c > > @@ -109,7 +109,8 @@ void task_work_run(void) > > * the first entry == work, cmpxchg(task_works) should > > * fail, but it can play with *work and other entries. > > */ > > - raw_spin_unlock_wait(&task->pi_lock); > > + raw_spin_lock(&task->pi_lock); > > + raw_spin_unlock(&task->pi_lock); > > Well, bit the you need spin_lock_irq(). And this is one of the reasons > why I personally think unlock_wait have some sense... Good catch, and I clearly need to double-check the other commits for any need to disable interrupts. Anyway, like this, with the addition of a flags variable, correct? > > + raw_spin_lock_irq(&task->pi_lock); > > + raw_spin_unlock_irq(&task->pi_lock); I agree that the spin_unlock_wait() implementations would avoid the deadlock with an acquisition from an interrupt handler, while also avoiding the need to momentarily disable interrupts. The ->pi_lock is a per-task lock, so I am assuming (perhaps naively) that contention is not a problem. So is the overhead of interrupt disabling likely to be noticeable here? Thanx, Paul