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 4A415C43334 for ; Thu, 9 Jun 2022 19:04:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234277AbiFITEI (ORCPT ); Thu, 9 Jun 2022 15:04:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229632AbiFITEH (ORCPT ); Thu, 9 Jun 2022 15:04:07 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 058B53F32D; Thu, 9 Jun 2022 12:04:07 -0700 (PDT) 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 9485861DF3; Thu, 9 Jun 2022 19:04:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C24DBC34114; Thu, 9 Jun 2022 19:04:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1654801445; bh=Yxnu6+83FYCfv/3NbAs8M+FkZ+oJRuDX8jaMn/PQaZE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DPDtpREhdB0j8JRKxYabn/GSmhFRQx135HzaS1QEKqIVh/3OLWcUqgRccNEM25gmk kG/OrJ39Z46ozUpCD4lB0Pz1Cgw5Nr0wS2LvRNpnFS3G1qnalODO0aE13KHfgq2aVF RBiVXksCRrbDV3G+6tdZE7M8qB5p84hUf24cfmQT69pB4ht/PfI68SUxb2hijm/Alk Iy9ZomiMariI7kTxRnfRkGzQdVh+RKRQraiVWC+Xd/Y3laedlgOxz6E566fV4n10Vd 4RCPFzR938EQgajfXo30ffAkTSTF2nYqegz7D/8H6zPQrMmQALtMa5fIpBWwlTlMaX oQLbte0bNq8JA== Date: Fri, 10 Jun 2022 03:03:58 +0800 From: Gao Xiang To: David Howells Cc: jlayton@kernel.org, Alexander Viro , Dominique Martinet , Mike Marshall , Gao Xiang , linux-afs@lists.infradead.org, v9fs-developer@lists.sourceforge.net, devel@lists.orangefs.org, linux-erofs@lists.ozlabs.org, linux-cachefs@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] iov_iter: Fix iter_xarray_get_pages{,_alloc}() Message-ID: Mail-Followup-To: David Howells , jlayton@kernel.org, Alexander Viro , Dominique Martinet , Mike Marshall , Gao Xiang , linux-afs@lists.infradead.org, v9fs-developer@lists.sourceforge.net, devel@lists.orangefs.org, linux-erofs@lists.ozlabs.org, linux-cachefs@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <165476202136.3999992.433442175457370240.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <165476202136.3999992.433442175457370240.stgit@warthog.procyon.org.uk> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jun 09, 2022 at 09:07:01AM +0100, David Howells wrote: > The maths at the end of iter_xarray_get_pages() to calculate the actual > size doesn't work under some circumstances, such as when it's been asked to > extract a partial single page. Various terms of the equation cancel out > and you end up with actual == offset. The same issue exists in > iter_xarray_get_pages_alloc(). > > Fix these to just use min() to select the lesser amount from between the > amount of page content transcribed into the buffer, minus the offset, and > the size limit specified. > > This doesn't appear to have caused a problem yet upstream because network > filesystems aren't getting the pages from an xarray iterator, but rather > passing it directly to the socket, which just iterates over it. Cachefiles > *does* do DIO from one to/from ext4/xfs/btrfs/etc. but it always asks for > whole pages to be written or read. > > Fixes: 7ff5062079ef ("iov_iter: Add ITER_XARRAY") > Reported-by: Jeff Layton > Signed-off-by: David Howells > cc: Alexander Viro > cc: Dominique Martinet > cc: Mike Marshall > cc: Gao Xiang > cc: linux-afs@lists.infradead.org > cc: v9fs-developer@lists.sourceforge.net > cc: devel@lists.orangefs.org > cc: linux-erofs@lists.ozlabs.org > cc: linux-cachefs@redhat.com > cc: linux-fsdevel@vger.kernel.org Looks good to me, Reviewed-by: Gao Xiang Thanks, Gao Xiang > --- > > lib/iov_iter.c | 20 ++++---------------- > 1 file changed, 4 insertions(+), 16 deletions(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index 834e1e268eb6..814f65fd0c42 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -1434,7 +1434,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, > { > unsigned nr, offset; > pgoff_t index, count; > - size_t size = maxsize, actual; > + size_t size = maxsize; > loff_t pos; > > if (!size || !maxpages) > @@ -1461,13 +1461,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, > if (nr == 0) > return 0; > > - actual = PAGE_SIZE * nr; > - actual -= offset; > - if (nr == count && size > 0) { > - unsigned last_offset = (nr > 1) ? 0 : offset; > - actual -= PAGE_SIZE - (last_offset + size); > - } > - return actual; > + return min(nr * PAGE_SIZE - offset, maxsize); > } > > /* must be done on non-empty ITER_IOVEC one */ > @@ -1602,7 +1596,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i, > struct page **p; > unsigned nr, offset; > pgoff_t index, count; > - size_t size = maxsize, actual; > + size_t size = maxsize; > loff_t pos; > > if (!size) > @@ -1631,13 +1625,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i, > if (nr == 0) > return 0; > > - actual = PAGE_SIZE * nr; > - actual -= offset; > - if (nr == count && size > 0) { > - unsigned last_offset = (nr > 1) ? 0 : offset; > - actual -= PAGE_SIZE - (last_offset + size); > - } > - return actual; > + return min(nr * PAGE_SIZE - offset, maxsize); > } > > ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, > >