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Subject: Re: [PATCH v4 4/9] nfsd: ensure we use ctime_peek to grab the
 inode->i_ctime
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
        Amir Goldstein <amir73il@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Neil Brown <neilb@suse.de>,
        Matthew Wilcox <willy@infradead.org>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Theodore T'so <tytso@mit.edu>, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        Namjae Jeon <linkinjeon@kernel.org>,
        Steve French <sfrench@samba.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Tom Talpey <tom@talpey.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
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Date:   Thu, 18 May 2023 11:31:45 -0400
In-Reply-To: <2B6A4DDD-0356-4765-9CED-B22A29767254@oracle.com>
References: <20230518114742.128950-1-jlayton@kernel.org>
         <20230518114742.128950-5-jlayton@kernel.org>
         <2B6A4DDD-0356-4765-9CED-B22A29767254@oracle.com>
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On Thu, 2023-05-18 at 13:43 +0000, Chuck Lever III wrote:
>=20
> > On May 18, 2023, at 7:47 AM, Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > If getattr fails, then nfsd can end up scraping the time values directl=
y
> > out of the inode for pre and post-op attrs. This may or may not be the
> > right thing to do, but for now make it at least use ctime_peek in this
> > situation to ensure that the QUERIED flag is masked.
>=20
> That code comes from:
>=20
> commit 39ca1bf624b6b82cc895b0217889eaaf572a7913
> Author:     Amir Goldstein <amir73il@gmail.com>
> AuthorDate: Wed Jan 3 17:14:35 2018 +0200
> Commit:     J. Bruce Fields <bfields@redhat.com>
> CommitDate: Thu Feb 8 13:40:17 2018 -0500
>=20
>     nfsd: store stat times in fill_pre_wcc() instead of inode times
>=20
>     The time values in stat and inode may differ for overlayfs and stat t=
ime
>     values are the correct ones to use. This is also consistent with the =
fact
>     that fill_post_wcc() also stores stat time values.
>=20
>     This means introducing a stat call that could fail, where previously =
we
>     were just copying values out of the inode.  To be conservative about
>     changing behavior, we fall back to copying values out of the inode in
>     the error case.  It might be better just to clear fh_pre_saved (thoug=
h
>     note the BUG_ON in set_change_info).
>=20
>     Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>     Signed-off-by: J. Bruce Fields <bfields@redhat.com>
>=20
> I was thinking it might have been added to handle odd corner
> cases around re-exporting NFS mounts, but that does not seem
> to be the case.
>=20
> The fh_getattr() can fail for legitimate reasons -- like the
> file is in the middle of being deleted or renamed over -- I
> would think. This code should really deal with that by not
> adding pre-op attrs, since they are optional.
>=20

That sounds fine to me. I'll plan to drop this patch from the series and
I'll send a separate patch to just remove those branches altogether
(which should DTRT).

--=20
Jeff Layton <jlayton@kernel.org>