Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752670AbaB0MGw (ORCPT ); Thu, 27 Feb 2014 07:06:52 -0500 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:59553 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751048AbaB0MGt (ORCPT ); Thu, 27 Feb 2014 07:06:49 -0500 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.0.1 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20120718-3 Message-ID: <530F2A2D.50307@jp.fujitsu.com> Date: Thu, 27 Feb 2014 21:06:05 +0900 From: Yasuaki Ishimatsu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Tang Chen CC: , , , , , , , , Subject: Re: [PATCH 2/2] aio, mem-hotplug: Add memory barrier to aio ring page migration. References: <1393497616-16428-1-git-send-email-tangchen@cn.fujitsu.com> <1393497616-16428-3-git-send-email-tangchen@cn.fujitsu.com> In-Reply-To: <1393497616-16428-3-git-send-email-tangchen@cn.fujitsu.com> Content-Type: text/plain; charset="ISO-2022-JP" Content-Transfer-Encoding: 7bit X-SecurityPolicyCheck-GC: OK by FENCE-Mail Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Tang, (2014/02/27 19:40), Tang Chen wrote: > When doing aio ring page migration, we migrated the page, and update > ctx->ring_pages[]. Like the following: > > aio_migratepage() > |-> migrate_page_copy(new, old) > | ...... /* Need barrier here */ > |-> ctx->ring_pages[idx] = new > > Actually, we need a memory barrier between these two operations. > Otherwise, if ctx->ring_pages[] is updated before memory copy due to > the compiler optimization, other processes may have an opportunity > to access to the not fully initialized new ring page. > > So add a wmb to synchronize them. > > Reported-by: Yasuaki Ishimatsu > Signed-off-by: Tang Chen > --- > fs/aio.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/fs/aio.c b/fs/aio.c > index 50c089c..f0ed838 100644 > --- a/fs/aio.c > +++ b/fs/aio.c > @@ -327,6 +327,14 @@ static int aio_migratepage(struct address_space *mapping, struct page *new, > pgoff_t idx; > spin_lock_irqsave(&ctx->completion_lock, flags); > migrate_page_copy(new, old); > + > + /* > + * Ensure memory copy is finished before updating > + * ctx->ring_pages[]. Otherwise other processes may access to > + * new ring pages which are not fully initialized. > + */ > + smp_wmb(); > + If you put smp_wmb() here, you should put smp_rmb() before kmap() in aio_read_events_ring(). Thanks, Yasuaki Ishimatsu > idx = old->index; > if (idx < (pgoff_t)ctx->nr_pages) { > /* And only do the move if things haven't changed */ > -- 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/