Re: [RFC PATCH] NFSD: Force all NFSv4.2 COPY requests to be synchronous

[Dai Ngo <dai.ngo@oracle.com>]

On 5/6/24 2:04 PM, cel@kernel.org wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>
> We've discovered that delivering a CB_OFFLOAD operation can be
> unreliable in some pretty unremarkable situations,

Since the fore and back channel use the same connection so I assume
this is not a connection related problem.

Sounds like this is a bug that we should find and fix if possible
instead of work around it. Do you know any scenarios where the
CB_OFFLOAD operation is unreliable?

-Dai

>   and the Linux
> NFS client does not yet support sending an OFFLOAD_STATUS
> operation to probe whether an asynchronous COPY operation has
> finished. On Linux NFS clients, COPY can hang until manually
> interrupted.
>
> I've tried a couple of remedies, but so far the side-effects are
> worse than the disease. For now, force COPY operations to be
> synchronous so that the use of CB_OFFLOAD is avoided entirely.
>
> I have some patches that add an OFFLOAD_STATUS implementation to the
> Linux NFS client, but that is not likely to fix older clients.
>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>   fs/nfsd/nfs4proc.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index ea3cc3e870a7..12722c709cc6 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1807,6 +1807,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>   	__be32 status;
>   	struct nfsd4_copy *async_copy = NULL;
>   
> +	/*
> +	 * Currently, async COPY is not reliable. Force all COPY
> +	 * requests to be synchronous to avoid client application
> +	 * hangs waiting for completion.
> +	 */
> +	nfsd4_copy_set_sync(copy, true);
> +
>   	copy->cp_clp = cstate->clp;
>   	if (nfsd4_ssc_is_inter(copy)) {
>   		trace_nfsd_copy_inter(copy);
>
> base-commit: 939cb14d51a150e3c12ef7a8ce0ba04ce6131bd2