linux-kernel - Re: [PATCH v2 0/2] nfsd: sanely handle inabilty to fetch pre/post attributes

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Message-id: <168988936713.11078.5407820394334916284@noble.neil.brown.name>
Date:   Fri, 21 Jul 2023 07:42:47 +1000
From:   "NeilBrown" <neilb@...e.de>
To:     "Jeff Layton" <jlayton@...nel.org>
Cc:     "Chuck Lever" <chuck.lever@...cle.com>,
        "Olga Kornievskaia" <kolga@...app.com>,
        "Dai Ngo" <Dai.Ngo@...cle.com>, "Tom Talpey" <tom@...pey.com>,
        "Boyang Xue" <bxue@...hat.com>, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, "Jeff Layton" <jlayton@...nel.org>
Subject: Re: [PATCH v2 0/2] nfsd: sanely handle inabilty to fetch pre/post attributes

On Fri, 21 Jul 2023, Jeff Layton wrote:
> Boyang reported tripping the BUG_ON in set_change_info. While we
> couldn't confirm it, one way this could happen would be for nfsd_lookup
> to succeed and then for fh_fill_both_attrs to fail.
> 
> This patchset attempts to (sanely) fix this, usually by aborting the
> operation if fetching the pre attributes fails. Post-op attribute fetch
> handling is more difficult to deal with however since we've already done
> the operation, so this has it just fudge the change_info4 if that
> occurs.

I think both v3 and v4 allow a reply that says "the operation was a
success but there are no post-op attrs".  With v4 you can say "there is
no change-attr, but here are some other attrs".  I think.

Our xdr-encoding doesn't make that easy, but it is just a "simple matter
of coding".  If you think it is worth it.

NeilBrown


> 
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
> Changes in v2:
> - make fh_fill_*_attrs return an error and have the callers handle it
> - rework of set_change_info, to better handle missing pre/post attrs
> 
> ---
> Jeff Layton (2):
>       nfsd: handle failure to collect pre/post-op attrs more sanely
>       nfsd: remove unsafe BUG_ON from set_change_info
> 
>  fs/nfsd/nfs3proc.c |  4 +++-
>  fs/nfsd/nfs4proc.c | 45 +++++++++++++++++++++++++++++++++------
>  fs/nfsd/nfsfh.c    | 26 ++++++++++++++---------
>  fs/nfsd/nfsfh.h    |  6 +++---
>  fs/nfsd/vfs.c      | 62 ++++++++++++++++++++++++++++++++++--------------------
>  fs/nfsd/xdr4.h     | 11 ----------
>  6 files changed, 100 insertions(+), 54 deletions(-)
> ---
> base-commit: 070f391ca4d48e1750ee6108eb44f751a9e9448e
> change-id: 20230720-bz2223560-9c4690a8217b
> 
> Best regards,
> -- 
> Jeff Layton <jlayton@...nel.org>
> 
>