linux-kernel - Re: [PATCH 7/8] nfsd: clean up and amend comments around nfsd4_cb_sequence

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Message-ID: <8a6e1930-feee-47f8-8260-874b9c47f20e@oracle.com>
Date: Fri, 24 Jan 2025 09:43:30 -0500
From: Chuck Lever <chuck.lever@...cle.com>
To: Jeff Layton <jlayton@...nel.org>, Neil Brown <neilb@...e.de>,
        Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>,
        Tom Talpey <tom@...pey.com>, "J. Bruce Fields" <bfields@...ldses.org>,
        Kinglong Mee <kinglongmee@...il.com>,
        Trond Myklebust <trondmy@...nel.org>, Anna Schumaker <anna@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 7/8] nfsd: clean up and amend comments around
 nfsd4_cb_sequence_done()

On 1/23/25 3:25 PM, Jeff Layton wrote:
> Add a new kerneldoc header, and clean up the comments a bit.

Usually I'm in favor of kdoc headers, but here, it's a static function
whose address is not shared outside of this source file. The only
documentation need is the meaning of the return code, IMO.


> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>   fs/nfsd/nfs4callback.c | 26 ++++++++++++++++++++------
>   1 file changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> index 6e0561f3b21bd850b0387b5af7084eb05e818231..415fc8aae0f47c36f00b2384805c7a996fb1feb0 100644
> --- a/fs/nfsd/nfs4callback.c
> +++ b/fs/nfsd/nfs4callback.c
> @@ -1325,6 +1325,17 @@ static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
>   	rpc_call_start(task);
>   }
>   
> +/**
> + * nfsd4_cb_sequence_done - process the result of a CB_SEQUENCE
> + * @task: rpc_task
> + * @cb: nfsd4_callback for this call
> + *
> + * For minorversion 0, there is no CB_SEQUENCE. Only restart the call
> + * if the callback RPC client was killed. For v4.1+ the error handling
> + * is more sophisticated.

It would be much clearer to pull the 4.0 error handling out of this
function, which is named "cb_/sequence/_done".

Perhaps the need_restart label can be hoisted into nfsd4_cb_done() ?


> + *
> + * Returns true if reply processing should continue.
> + */
>   static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback *cb)
>   {
>   	struct nfs4_client *clp = cb->cb_clp;
> @@ -1334,11 +1345,11 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
>   	if (!clp->cl_minorversion) {
>   		/*
>   		 * If the backchannel connection was shut down while this
> -		 * task was queued, we need to resubmit it after setting up
> -		 * a new backchannel connection.
> +		 * task was queued, resubmit it after setting up a new
> +		 * backchannel connection.
>   		 *
> -		 * Note that if we lost our callback connection permanently
> -		 * the submission code will error out, so we don't need to
> +		 * Note that if the callback connection is permanently lost,
> +		 * the submission code will error out. There is no need to
>   		 * handle that case here.
>   		 */
>   		if (RPC_SIGNALLED(task))
> @@ -1355,8 +1366,6 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
>   	switch (cb->cb_seq_status) {
>   	case 0:
>   		/*
> -		 * No need for lock, access serialized in nfsd4_cb_prepare
> -		 *
>   		 * RFC5661 20.9.3
>   		 * If CB_SEQUENCE returns an error, then the state of the slot
>   		 * (sequence ID, cached reply) MUST NOT change.
> @@ -1365,6 +1374,11 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
>   		ret = true;
>   		break;
>   	case -ESERVERFAULT:
> +		/*
> +		 * Client returned NFS4_OK, but decoding failed. Mark the
> +		 * backchannel as faulty, but don't retransmit since the
> +		 * call was successful.
> +		 */
>   		++session->se_cb_seq_nr[cb->cb_held_slot];
>   		nfsd4_mark_cb_fault(cb->cb_clp);
>   		break;

This old code abuses the meaning of ESERVERFAULT IMO. NFS4ERR_BADXDR is
a better choice. But why call mark_cb_fault in this case?

Maybe split this clean-up into a separate patch.


-- 
Chuck Lever