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

[cel@kernel.org]

From: Chuck Lever <chuck.lever@oracle.com>

We've discovered that delivering a CB_OFFLOAD operation can be
unreliable in some pretty unremarkable situations, 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
-- 
2.44.0