From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756116AbbCMXYl (ORCPT ); Fri, 13 Mar 2015 19:24:41 -0400 Received: from mail-ie0-f177.google.com ([209.85.223.177]:36237 "EHLO mail-ie0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755399AbbCMXYe (ORCPT ); Fri, 13 Mar 2015 19:24:34 -0400 Date: Fri, 13 Mar 2015 16:24:32 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Jens Axboe cc: Lars Ellenberg , linux-kernel@vger.kernel.org, drbd-user@lists.linbit.com Subject: Re: [patch 1/2] block, drbd: fix drbd_req_new() initialization In-Reply-To: Message-ID: References: <54FB98F3.2050308@fb.com> <54FB9FE2.5040707@fb.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 7 Mar 2015, David Rientjes 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. > > > > 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. > Jens, are these two patches going to be merged into linux-block? Thanks.