Date:   Thu, 18 Apr 2019 11:13:12 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Scott Mayhew <smayhew@redhat.com>
Cc:     jlayton@kernel.org, linux-nfs@vger.kernel.org
Subject: Re: [PATCH] nfsd: CB_RECALL can race with FREE_STATEID
Message-ID: <20190418151312.GB29274@fieldses.org>
References: <20190418132400.24161-1-smayhew@redhat.com>
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On Thu, Apr 18, 2019 at 09:24:00AM -0400, Scott Mayhew wrote:
> While trying to track down some issues involving large numbers of
> delegations being recalled/revoked, I caught the server setting
> SEQ4_STATUS_CB_PATH_DOWN while the client was actively responding to
> CB_RECALLs.  It turns out that the client had already done a
> TEST_STATEID and FREE_STATEID for a delegation being recalled by the
> time it received the CB_RECALL.

That's interesting, thanks!

This exception seems awfully narrow, though.

If we get back any NFS-level error at all, then I think the callback
channel is working (am I wrong?) and telling the client to set up a new
one is probably not going to help.  The best we can do is probably just
give up and let the client deal with the ensuing
RECALLABLE_STATE_REVOKED flag.

--b.

> 
> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> ---
>  fs/nfsd/nfs4state.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 6a45fb00c5fc..e88e429133a8 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -3958,6 +3958,14 @@ static int nfsd4_cb_recall_done(struct nfsd4_callback *cb,
>  			rpc_delay(task, 2 * HZ);
>  			return 0;
>  		}
> +		/*
> +		 * Race: client may have done a FREE_STATEID before
> +		 * receiving the CB_RECALL.
> +		 */
> +		if (dp->dl_stid.sc_type == NFS4_REVOKED_DELEG_STID &&
> +				refcount_read(&dp->dl_stid.sc_count) == 1 &&
> +				list_empty(&dp->dl_recall_lru))
> +			return 1;
>  		/*FALLTHRU*/
>  	default:
>  		return -1;
> -- 
> 2.17.2