From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751200AbbCHBpK (ORCPT ); Sat, 7 Mar 2015 20:45:10 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:25567 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750752AbbCHBpG (ORCPT ); Sat, 7 Mar 2015 20:45:06 -0500 Message-ID: <54FBA9A3.9070606@fb.com> Date: Sat, 7 Mar 2015 18:45:07 -0700 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: David Rientjes CC: Lars Ellenberg , , Subject: Re: [patch 1/2] block, drbd: fix drbd_req_new() initialization References: <54FB98F3.2050308@fb.com> <54FB9FE2.5040707@fb.com> In-Reply-To: Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.54.13] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.13.68,1.0.33,0.0.0000 definitions=2015-03-08_01:2015-03-06,2015-03-07,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 kscore.is_bulkscore=6.85201340111519e-11 kscore.compositescore=0 circleOfTrustscore=0 compositescore=0.985052395226116 suspectscore=2 recipient_domain_to_sender_totalscore=0 phishscore=0 bulkscore=0 kscore.is_spamscore=0 rbsscore=0.985052395226116 recipient_to_sender_totalscore=0 recipient_domain_to_sender_domain_totalscore=0 spamscore=0 recipient_to_sender_domain_totalscore=0 urlsuspectscore=0.985052395226116 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1503080017 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/07/2015 06:27 PM, David Rientjes wrote: > On Sat, 7 Mar 2015, Jens Axboe wrote: > >>>>> mempool_alloc() does not support __GFP_ZERO since elements may come from >>>>> memory that has already been released by mempool_free(). >>>>> >>>>> Remove __GFP_ZERO from mempool_alloc() in drbd_req_new() and properly >>>>> initialize it to 0. >>>> >>>> You should add it to mempool instead, avoid having this issue show up for >>>> other folks as well. It'd be trivial to do. Normal ->alloc() should honor >>>> __GFP_ZERO, just do the same manually for removing an item from the internal >>>> pool. >>>> >>> >>> Umm, it's not trivial to do and wouldn't make sense to do it. Mempools >> >> Uhm, it would make sense, though. >> > > Disagree, I don't think we should extend mempool to know the element size, > modify every user of mempool to pass it in, and keep it consistent with > mempool_alloc_t for the benefit of __GFP_ZERO for this one buggy caller. > Most users don't need __GFP_ZERO and just overwrite the entire element > after mempool_alloc() and it would be an unnecessary overhead to even > check for the bit set. So it wouldn't make sense in terms of performance > or maintainability. My point is that conceptually, of course it makes sense to do and it _should_ do it. We don't have the size, too bad, I don't disagree that adding it just for this is necessarily the best idea. >>> don't know the element size, in other words it wouldn't know the length to >>> memset() to 0 for mempool_alloc(). It shouldn't be modified to know the >>> element size since elements are allocated by the implementation of >>> mempool_alloc_t and they could easily become inconsistent. This patch is >>> what you want to merge, really. >>> >> >> I forgot we don't have the size in there. Then I would suggest adding a >> WARN_ON() for __GFP_ZERO being set in mempool_alloc(), at the very least. >> > > There is, it's a VM_WARN_ON_ONCE() that will show up if you configure > CONFIG_DEBUG_VM. OK, that's good enough then. -- Jens Axboe