From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932820Ab2HXCV0 (ORCPT ); Thu, 23 Aug 2012 22:21:26 -0400 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:59069 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932906Ab2HXCVT (ORCPT ); Thu, 23 Aug 2012 22:21:19 -0400 Message-ID: <5036E514.1090509@linux.vnet.ibm.com> Date: Fri, 24 Aug 2012 10:21:08 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Minchan Kim CC: Seth Jennings , Greg Kroah-Hartman , Andrew Morton , Nitin Gupta , Konrad Rzeszutek Wilk , Dan Magenheimer , linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org Subject: Re: [PATCH 0/2] revert changes to zcache_do_preload() References: <1345735991-6995-1-git-send-email-sjenning@linux.vnet.ibm.com> <20120823205648.GA2066@barrios> <5036AA38.6010400@linux.vnet.ibm.com> <20120823232845.GE5369@bbox> In-Reply-To: <20120823232845.GE5369@bbox> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12082402-2000-0000-0000-000008D3DF2A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/24/2012 07:28 AM, Minchan Kim wrote: > On Thu, Aug 23, 2012 at 05:10:00PM -0500, Seth Jennings wrote: >> On 08/23/2012 03:56 PM, Minchan Kim wrote: >>> Hi Seth, >>> >>> On Thu, Aug 23, 2012 at 10:33:09AM -0500, Seth Jennings wrote: >>>> This patchset fixes a regression in 3.6 by reverting two dependent >>>> commits that made changes to zcache_do_preload(). >>>> >>>> The commits undermine an assumption made by tmem_put() in >>>> the cleancache path that preemption is disabled. This change >>>> introduces a race condition that can result in the wrong page >>>> being returned by tmem_get(), causing assorted errors (segfaults, >>>> apparent file corruption, etc) in userspace. >>>> >>>> The corruption was discussed in this thread: >>>> https://lkml.org/lkml/2012/8/17/494 >>> >>> I think changelog isn't enough to explain what's the race. >>> Could you write it down in detail? >> >> I didn't come upon this solution via code inspection, but >> rather through discovering that the issue didn't exist in >> v3.5 and just looking at the changes since then. > > Okay, then, why do you think the patchsets are culprit? > I didn't look the cleanup patch series of Xiao at that time > so I can be wrong but as I just look through patch of > "zcache: optimize zcache_do_preload", I can't find any fault > because zcache_put_page checks irq_disable so we don't need > to disable preemption so it seems that patch is correct to me. > If the race happens by preemption, BUG_ON in zcache_put_page > should catch it. Confused me too! And the first patch just do the cleanup, it is not different before the patch and after the patch, what i missed?