From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f42.google.com (mail-pb0-f42.google.com [209.85.160.42]) by kanga.kvack.org (Postfix) with ESMTP id 3B9236B0031 for ; Sun, 5 Jan 2014 19:12:32 -0500 (EST) Received: by mail-pb0-f42.google.com with SMTP id uo5so17945021pbc.1 for ; Sun, 05 Jan 2014 16:12:31 -0800 (PST) Received: from LGEMRELSE6Q.lge.com (LGEMRELSE6Q.lge.com. [156.147.1.121]) by mx.google.com with ESMTP id ll1si34697635pab.318.2014.01.05.16.12.29 for ; Sun, 05 Jan 2014 16:12:30 -0800 (PST) Date: Mon, 6 Jan 2014 09:12:37 +0900 From: Joonsoo Kim 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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, 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