nfsd: nfserr_jukebox in nlm_fopen should lead to a retry

When v3 NLM request finds a conflicting delegation, it triggers
a delegation recall and nfsd_open fails with EAGAIN. nfsd_open
then translates EAGAIN into nfserr_jukebox. In nlm_fopen, instead
of returning nlm_failed for when there is a conflicting delegation,
drop this NLM request so that the client retries. Once delegation
is recalled and if a local lock is claimed, a retry would lead to
nfsd returning a nlm_lck_blocked error or a successful nlm lock.

Fixes: d343fce ("[PATCH] knfsd: Allow lockd to drop replies as appropriate")
Cc: stable@vger.kernel.org # v6.6
Signed-off-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: Olga Kornievskaia

fs/nfsd/lockd.c

@@ -57,6 +57,21 @@ nlm_fopen(struct svc_rqst *rqstp, struct nfs_fh *f, struct file **filp,
 	switch (nfserr) {
 	case nfs_ok:
 		return 0;
+	case nfserr_jukebox:
+		/* this error can indicate a presence of a conflicting
+		 * delegation to an NLM lock request. Options are:
+		 * (1) For now, drop this request and make the client
+		 * retry. When delegation is returned, client's lock retry
+		 * will complete.
+		 * (2) NLM4_DENIED as per "spec" signals to the client
+		 * that the lock is unavailable now but client can retry.
+		 * Linux client implementation does not. It treats
+		 * NLM4_DENIED same as NLM4_FAILED and errors the request.
+		 * (3) For the future, treat this as blocked lock and try
+		 * to callback when the delegation is returned but might
+		 * not have a proper lock request to block on.
+		 */
+		fallthrough;
 	case nfserr_dropit:
 		return nlm_drop_reply;
 	case nfserr_stale: