From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f200.google.com (mail-qt0-f200.google.com [209.85.216.200]) by kanga.kvack.org (Postfix) with ESMTP id C67316B0292 for ; Tue, 6 Jun 2017 11:56:05 -0400 (EDT) Received: by mail-qt0-f200.google.com with SMTP id x53so85137687qtx.14 for ; Tue, 06 Jun 2017 08:56:05 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id z7si16902708qka.218.2017.06.06.08.56.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Jun 2017 08:56:04 -0700 (PDT) Date: Tue, 6 Jun 2017 17:56:01 +0200 From: Oleg Nesterov Subject: Re: double call identical release when there is a race hitting Message-ID: <20170606155600.GA17705@redhat.com> References: <5936B098.6020807@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5936B098.6020807@huawei.com> Sender: owner-linux-mm@kvack.org List-ID: To: zhong jiang Cc: Michal Hocko , Vlastimil Babka , David Rientjes , Hugh Dickins , Linux Memory Management List , LKML , Xishi Qiu I can't answer authoritatively, but On 06/06, zhong jiang wrote: > > Hi > > when I review the code, I find the following scenario will lead to a race , > but I am not sure whether the real issue will hit or not. > > cpu1 cpu2 > exit_mmap mmu_notifier_unregister > __mmu_notifier_release srcu_read_lock > srcu_read_lock > mm->ops->release(mn, mm) mm->ops->release(mn,mm) > srcu_read_unlock srcu_read_unlock > > > obviously, the specified mm will call identical release function when > the related condition satisfy. is it right? I think you are right, this is possible, perhaps the comments should mention this explicitly. See the changelog in d34883d4e35c0a994e91dd847a82b4c9e0c31d83 "mm: mmu_notifier: re-fix freed page still mapped in secondary MMU": "multiple ->release() callouts", we needn't care it too much ... Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751471AbdFFP4F (ORCPT ); Tue, 6 Jun 2017 11:56:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41338 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751388AbdFFP4E (ORCPT ); Tue, 6 Jun 2017 11:56:04 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com ED02ADF86E Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=oleg@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com ED02ADF86E Date: Tue, 6 Jun 2017 17:56:01 +0200 From: Oleg Nesterov To: zhong jiang Cc: Michal Hocko , Vlastimil Babka , David Rientjes , Hugh Dickins , Linux Memory Management List , LKML , Xishi Qiu Subject: Re: double call identical release when there is a race hitting Message-ID: <20170606155600.GA17705@redhat.com> References: <5936B098.6020807@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5936B098.6020807@huawei.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 06 Jun 2017 15:56:04 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I can't answer authoritatively, but On 06/06, zhong jiang wrote: > > Hi > > when I review the code, I find the following scenario will lead to a race , > but I am not sure whether the real issue will hit or not. > > cpu1 cpu2 > exit_mmap mmu_notifier_unregister > __mmu_notifier_release srcu_read_lock > srcu_read_lock > mm->ops->release(mn, mm) mm->ops->release(mn,mm) > srcu_read_unlock srcu_read_unlock > > > obviously, the specified mm will call identical release function when > the related condition satisfy. is it right? I think you are right, this is possible, perhaps the comments should mention this explicitly. See the changelog in d34883d4e35c0a994e91dd847a82b4c9e0c31d83 "mm: mmu_notifier: re-fix freed page still mapped in secondary MMU": "multiple ->release() callouts", we needn't care it too much ... Oleg.