From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AD10C433EF for ; Fri, 28 Jan 2022 20:31:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232184AbiA1UbN (ORCPT ); Fri, 28 Jan 2022 15:31:13 -0500 Received: from sandeen.net ([63.231.237.45]:41062 "EHLO sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232131AbiA1UbM (ORCPT ); Fri, 28 Jan 2022 15:31:12 -0500 Received: from [10.0.0.147] (liberator.sandeen.net [10.0.0.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by sandeen.net (Postfix) with ESMTPSA id 21ED378FD; Fri, 28 Jan 2022 14:30:59 -0600 (CST) Message-ID: Date: Fri, 28 Jan 2022 14:31:11 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Content-Language: en-US To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org References: <164263784199.860211.7509808171577819673.stgit@magnolia> <164263806915.860211.11553766371419430734.stgit@magnolia> From: Eric Sandeen Subject: Re: [PATCH 41/45] libxfs: always initialize internal buffer map In-Reply-To: <164263806915.860211.11553766371419430734.stgit@magnolia> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 1/19/22 6:21 PM, Darrick J. Wong wrote: > From: Darrick J. Wong > > The __initbuf function is responsible for initializing the fields of an > xfs_buf. Buffers are always required to have a mapping, though in the > typical case there's only one mapping, so we can use the internal one. > > The single-mapping b_maps init code at the end of the function doesn't > quite get this right though -- if a single-mapping buffer in the cache > was allowed to expire and now is being repurposed, it'll come out with > b_maps == &__b_map, in which case we incorrectly skip initializing the > map. In this case b_nmaps must already be 1, right. And it's the bn and length in b_maps[0] that fail to be initialized? I wonder, then, if it's any more clear to reorganize it just a little bit, like: if (!bp->b_maps) { bp->b_maps = &bp->__b_map; bp->b_nmaps = 1; } if (bp->b_maps == &bp->__b_map) { bp->b_maps[0].bm_bn = bp->b_bn; bp->b_maps[0].bm_len = bp->b_length; } because AFAICT b_nmaps only needs to be reset to 1 if we didn't already get here with b_maps == &__b_map? If this is just navel-gazing I can leave it as is. If you think it's any clearer, I'll make the change. (or if I've gotten it completely wrong, sorry!) Thanks, -Eric > This has gone unnoticed until now because (AFAICT) the code paths > that use b_maps are the same ones that are called with multi-mapping > buffers, which are initialized correctly. > > Anyway, the improperly initialized single-mappings will cause problems > in upcoming patches where we turn b_bn into the cache key and require > the use of b_maps[0].bm_bn for the buffer LBA. Fix this. > > Signed-off-by: Darrick J. Wong > --- > libxfs/rdwr.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > > diff --git a/libxfs/rdwr.c b/libxfs/rdwr.c > index 5086bdbc..a55e3a79 100644 > --- a/libxfs/rdwr.c > +++ b/libxfs/rdwr.c > @@ -251,9 +251,11 @@ __initbuf(struct xfs_buf *bp, struct xfs_buftarg *btp, xfs_daddr_t bno, > bp->b_ops = NULL; > INIT_LIST_HEAD(&bp->b_li_list); > > - if (!bp->b_maps) { > - bp->b_nmaps = 1; > + if (!bp->b_maps) > bp->b_maps = &bp->__b_map; > + > + if (bp->b_maps == &bp->__b_map) { > + bp->b_nmaps = 1; > bp->b_maps[0].bm_bn = bp->b_bn; > bp->b_maps[0].bm_len = bp->b_length; > } >