From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id D85572C00A0 for ; Wed, 12 Feb 2014 05:53:04 +1100 (EST) Message-ID: <1392144772.23418.11.camel@pasglop> Subject: Re: [PATCH V2] powerpc: thp: Fix crash on mremap From: Benjamin Herrenschmidt To: Greg KH Date: Wed, 12 Feb 2014 05:52:52 +1100 In-Reply-To: <20140211173129.GB30336@kroah.com> References: <1391781117-19045-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20140211173129.GB30336@kroah.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linuxppc-dev@lists.ozlabs.org, paulus@samba.org, "Aneesh Kumar K.V" , stable@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2014-02-11 at 09:31 -0800, Greg KH wrote: > On Fri, Feb 07, 2014 at 07:21:57PM +0530, Aneesh Kumar K.V wrote: > > From: "Aneesh Kumar K.V" > > > > This patch fix the below crash > > > > NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440 > > LR [c0000000000439ac] .hash_page+0x18c/0x5e0 > > ... > > Call Trace: > > [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable) > > [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0 > > [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58 > > > > On ppc64 we use the pgtable for storing the hpte slot information and > > store address to the pgtable at a constant offset (PTRS_PER_PMD) from > > pmd. On mremap, when we switch the pmd, we need to withdraw and deposit > > the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset > > from new pmd. > > > > We also want to move the withdraw and deposit before the set_pmd so > > that, when page fault find the pmd as trans huge we can be sure that > > pgtable can be located at the offset. > > > > variant of upstream SHA1: b3084f4db3aeb991c507ca774337c7e7893ed04f > > for 3.12 stable series > > This doesn't look like a "variant", it looks totally different. Why > can't I just take the b3084f4db3aeb991c507ca774337c7e7893ed04f patch > (and follow-on fix) for 3.12? > > I _REALLY_ dislike patches that are totally different from Linus's tree > in stable trees, it has caused nothing but problems in the past. I don't think it applies... (I tried on an internal tree) but the affected function changed in 3.13 in various ways. Aneesh, please provide a more details explanation and whether we should backport those other changes too or whether this is not necessary. BTW. Aneesh, we need a 3.11.x one too Cheers, Ben.