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 5ACA9C433F5 for ; Fri, 28 Jan 2022 22:03:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241928AbiA1WD1 (ORCPT ); Fri, 28 Jan 2022 17:03:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229608AbiA1WD1 (ORCPT ); Fri, 28 Jan 2022 17:03:27 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B673C061714 for ; Fri, 28 Jan 2022 14:03:27 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CE00861EDF for ; Fri, 28 Jan 2022 22:03:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 26DFFC340E8; Fri, 28 Jan 2022 22:03:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1643407406; bh=kJYGbHyqe6ECe9FWfPDPbeV1QXkcaVLW/L3rb8mS5nU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hicoIthw/PtOIGZ4w0asD78I5XPq5VC9tQ01VqdpKKfQkhNkW8K/2bfPgEYjzE7tv nqa3Mb44H4P+g1sZkzmlLy48BDZ+gs85h1idh1HnN6uE7bgcIpUajBkNCprrmQ1YnU 4xnCL/89NOISoyLuHCaXpie5a8K7MrEBsgcgQKiqt8DnLbfli4/FzCOXZKdD4ntGjo 7T5C99N3MkOARPJzdmg5sh7MDjk2r/9r/9aLxZUwODiuT/wlrs+TKr0TEJTYMtgt88 Vj2WsKChnjc882QnQ4DGhECGG4MVq2nwbY6wFPIqhW0RNG1NWvaD9YadCOIom+Tcrm npiyUO1Aw0gJw== Date: Fri, 28 Jan 2022 14:03:25 -0800 From: "Darrick J. Wong" To: Eric Sandeen Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 41/45] libxfs: always initialize internal buffer map Message-ID: <20220128220325.GH13540@magnolia> References: <164263784199.860211.7509808171577819673.stgit@magnolia> <164263806915.860211.11553766371419430734.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Jan 28, 2022 at 02:31:11PM -0600, Eric Sandeen wrote: > 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? That would also work, though it's less obvious (to me anyway) that b_nmaps is always 1 when bp->b_maps == &bp->__b_map. --D > 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; > > } > >