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 7C132CD343C for ; Tue, 19 Sep 2023 05:32:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231283AbjISFcP (ORCPT ); Tue, 19 Sep 2023 01:32:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231128AbjISFcO (ORCPT ); Tue, 19 Sep 2023 01:32:14 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73FAC102; Mon, 18 Sep 2023 22:32:09 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11257C433C8; Tue, 19 Sep 2023 05:32:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1695101529; bh=6ETapI40ei8LUIBUtJd9POMEs+mJGY9nr0kwwV+6UAs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EZWgoFnbj5FHaNGPXmUdLdoUyMaU7r7iEAVj4YDfEEaR1JjTiwZNXCPK8b5QlwEah hY0voCIGyjvY3Bnr7sgf8WbmYNYd/iez6M6lSnzZ0g5Gxv075v/4QZduM7QQ8KYAOw QUCRSOw6a3yUECpLhO5B5IRL2EoFPeM3d5n6sqkmWpmwijRLb40aLsNi64h4IL2P4W 2Bh6hivEC547o0RsSWSIOmckIavNOA3s1/TsbISJvG7Bu46weZH6P5gF4JnoNEETlW nngCPgG/RzwPm6Sbtuh4Csgz7aP5pGRGu08q3lqKUgpaq5TqTuo+o9UwjcaTJjOoLa mgUHiTGW2LPfA== Date: Mon, 18 Sep 2023 22:32:08 -0700 From: "Darrick J. Wong" To: Ritesh Harjani Cc: willy@infradead.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 1/2] iomap: don't skip reading in !uptodate folios when unsharing a range Message-ID: <20230919053208.GH348018@frogsfrogsfrogs> References: <169507872536.772278.18183365318216726644.stgit@frogsfrogsfrogs> <87o7hy7nhp.fsf@doe.com> <20230919052434.GG348018@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230919052434.GG348018@frogsfrogsfrogs> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Mon, Sep 18, 2023 at 10:24:34PM -0700, Darrick J. Wong wrote: > On Tue, Sep 19, 2023 at 10:44:58AM +0530, Ritesh Harjani wrote: > > "Darrick J. Wong" writes: > > > > > From: Darrick J. Wong > > > > > > Prior to commit a01b8f225248e, we would always read in the contents of a > > > !uptodate folio prior to writing userspace data into the folio, > > > allocated a folio state object, etc. Ritesh introduced an optimization > > > that skips all of that if the write would cover the entire folio. > > > > > > Unfortunately, the optimization misses the unshare case, where we always > > > have to read in the folio contents since there isn't a data buffer > > > supplied by userspace. This can result in stale kernel memory exposure > > > if userspace issues a FALLOC_FL_UNSHARE_RANGE call on part of a shared > > > file that isn't already cached. > > > > > > This was caught by observing fstests regressions in the "unshare around" > > > mechanism that is used for unaligned writes to a reflinked realtime > > > volume when the realtime extent size is larger than 1FSB, > > > > I was wondering what is testcase that you are referring here to? > > Can you please tell the testcase no. and the mkfs / mount config options > > which I can use to observe the regression please? > > https://lore.kernel.org/linux-fsdevel/169507871947.772278.5767091361086740046.stgit@frogsfrogsfrogs/T/#m8081f74f4f1fcb862399aa1544be082aabe56765 > > (any xfs config with reflink enabled) *OH* you meant which testcase in the realtime reflink patchset. This testcase: https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/commit/tests/xfs/1919?h=djwong-wtf&id=56538e8882ac52e606882cfcab7e46dcb64d2a62 And this tag: https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/tag/?h=realtime-reflink-extsize_2023-09-12 If you rebase this branch against 6.6-rc1. Then you need this xfsprogs: https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfsprogs-dev.git/tag/?h=realtime-reflink-extsize_2023-09-12 and ... MKFS_OPTIONS='-d rtinherit=1, -n parent=1, -r extsize=28k,rtgroups=1' along with a SCRATCH_RTDE. I'm basically done porting djwong-dev to 6.6 and will likely have an initial patchbomb of more online fsck stuff for 6.7 in a few days. --D > --D > > > > though I think it applies to any shared file. > > > > > > Cc: ritesh.list@gmail.com, willy@infradead.org > > > Fixes: a01b8f225248e ("iomap: Allocate ifs in ->write_begin() early") > > > Signed-off-by: Darrick J. Wong > > > --- > > > fs/iomap/buffered-io.c | 6 ++++-- > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > > index ae8673ce08b1..0350830fc989 100644 > > > --- a/fs/iomap/buffered-io.c > > > +++ b/fs/iomap/buffered-io.c > > > @@ -640,11 +640,13 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos, > > > size_t poff, plen; > > > > > > /* > > > - * If the write completely overlaps the current folio, then > > > + * If the write or zeroing completely overlaps the current folio, then > > > * entire folio will be dirtied so there is no need for > > > * per-block state tracking structures to be attached to this folio. > > > + * For the unshare case, we must read in the ondisk contents because we > > > + * are not changing pagecache contents. > > > */ > > > - if (pos <= folio_pos(folio) && > > > + if (!(iter->flags & IOMAP_UNSHARE) && pos <= folio_pos(folio) && > > > pos + len >= folio_pos(folio) + folio_size(folio)) > > > return 0; > > >