linux-kernel - Re: [PATCH RFC] nfsd: set missing after_change as before

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Message-ID: <ZL6W0GqBSdlvVL2Y@tissot.1015granger.net>
Date:   Mon, 24 Jul 2023 11:20:48 -0400
From:   Chuck Lever <chuck.lever@...cle.com>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Neil Brown <neilb@...e.de>, Olga Kornievskaia <kolga@...app.com>,
        Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] nfsd: set missing after_change as before_change + 1

On Mon, Jul 24, 2023 at 10:53:39AM -0400, Jeff Layton wrote:
> In the event that we can't fetch post_op_attr attributes, we still need
> to set a value for the after_change. The operation has already happened,
> so we're not able to return an error at that point, but we do want to
> ensure that the client knows that its cache should be invalidated.
> 
> If we weren't able to fetch post-op attrs, then just set the
> after_change to before_change + 1. The atomic flag should already be
> clear in this case.
> 
> Suggested-by: Neil Brown <neilb@...e.de>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  fs/nfsd/nfs4proc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

I'm not sure this change makes any difference. The client would
possibly see the change value move forward then back. I'd think a
false "atomic" field and using the /same/ pre- and post-change would
be safer...?

But I'm intrigued enough to apply this to nfsd-next provisionally,
at least for testing and further review. It will appear a little
later today.


> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 3f6710c9c5c9..f0f318e78630 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -411,7 +411,7 @@ set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp)
>  	if (WARN_ON_ONCE(!fhp->fh_pre_saved))
>  		cinfo->before_change = 0;
>  	if (!fhp->fh_post_saved)
> -		cinfo->after_change = 0;
> +		cinfo->after_change = cinfo->before_change + 1;
>  }
>  
>  static __be32
> 
> ---
> base-commit: 97a5d0146ef443df148805a4e9c3c44111f14ab1
> change-id: 20230724-bz2223560-5ed6bc3a5db7
> 
> Best regards,
> -- 
> Jeff Layton <jlayton@...nel.org>
> 

-- 
Chuck Lever