From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx194.postini.com [74.125.245.194]) by kanga.kvack.org (Postfix) with SMTP id C12116B0044 for ; Thu, 23 Aug 2012 19:28:14 -0400 (EDT) Date: Fri, 24 Aug 2012 08:28:45 +0900 From: Minchan Kim Subject: Re: [PATCH 0/2] revert changes to zcache_do_preload() Message-ID: <20120823232845.GE5369@bbox> References: <1345735991-6995-1-git-send-email-sjenning@linux.vnet.ibm.com> <20120823205648.GA2066@barrios> <5036AA38.6010400@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5036AA38.6010400@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Seth Jennings Cc: 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, xiaoguangrong@linux.vnet.ibm.com 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. What do you mean? Do you have any clue in your mind? The commits undermine an assumption made by tmem_put() in the cleancache path that preemption is disabled. > > > And you should Cc'ed Xiao who is author of reverted patch. > > Thanks for adding Xiao. I meant to do this. For some reason > I thought that you submitted that patchset :-/ Even, I didn't notice that patchset at that time. :) > My bad. > > Seth > > -- > 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 -- Kind regards, Minchan Kim -- 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