Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752151AbaAFAMc (ORCPT ); Sun, 5 Jan 2014 19:12:32 -0500 Received: from LGEMRELSE6Q.lge.com ([156.147.1.121]:44322 "EHLO LGEMRELSE6Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751407AbaAFAMa (ORCPT ); Sun, 5 Jan 2014 19:12:30 -0500 X-AuditID: 9c930179-b7c89ae000006438-e3-52c9f4ebad1b Date: Mon, 6 Jan 2014 09:12:37 +0900 From: Joonsoo Kim To: David Gibson Cc: Andrew Morton , Rik van Riel , Mel Gorman , Michal Hocko , "Aneesh Kumar K.V" , KAMEZAWA Hiroyuki , Hugh Dickins , Davidlohr Bueso , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wanpeng Li , Naoya Horiguchi , Hillf Danton Subject: Re: [PATCH v3 03/14] mm, hugetlb: protect region tracking via newly introduced resv_map lock Message-ID: <20140106001237.GA696@lge.com> References: <1387349640-8071-1-git-send-email-iamjoonsoo.kim@lge.com> <1387349640-8071-4-git-send-email-iamjoonsoo.kim@lge.com> <20131221135819.GB12407@voom.fritz.box> <20131223010517.GB19388@lge.com> <20131224120012.GH12407@voom.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131224120012.GH12407@voom.fritz.box> User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 24, 2013 at 11:00:12PM +1100, David Gibson wrote: > On Mon, Dec 23, 2013 at 10:05:17AM +0900, Joonsoo Kim wrote: > > On Sun, Dec 22, 2013 at 12:58:19AM +1100, David Gibson wrote: > > > On Wed, Dec 18, 2013 at 03:53:49PM +0900, Joonsoo Kim wrote: > > > > There is a race condition if we map a same file on different processes. > > > > Region tracking is protected by mmap_sem and hugetlb_instantiation_mutex. > > > > When we do mmap, we don't grab a hugetlb_instantiation_mutex, but, > > > > grab a mmap_sem. This doesn't prevent other process to modify region > > > > structure, so it can be modified by two processes concurrently. > > > > > > > > To solve this, I introduce a lock to resv_map and make region manipulation > > > > function grab a lock before they do actual work. This makes region > > > > tracking safe. > > > > > > It's not clear to me if you're saying there is a list corruption race > > > bug in the existing code, or only that there will be if the > > > instantiation mutex goes away. > > > > Hello, > > > > The race exists in current code. > > Currently, region tracking is protected by either down_write(&mm->mmap_sem) or > > down_read(&mm->mmap_sem) + instantiation mutex. But if we map this hugetlbfs > > file to two different processes, holding a mmap_sem doesn't have any impact on > > the other process and concurrent access to data structure is possible. > > Ouch. In that case: > > Acked-by: David Gibson > > It would be really nice to add a testcase for this race to the > libhugetlbfs testsuite. Okay! I will add it. Thanks. -- 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/