[PATCH v2 1/2] NFSv4: Deal with atomic upgrades of an existing delegation

[Trond Myklebust <trond.myklebust@primarydata.com>]

Ensure that we deal correctly with the case where the server sends us a
newer instance of the same delegation. If the stateids match, but the
sequence numbers differ, then treat the new delegation as if it were
an atomic upgrade.

Signed-off-by: Trond Myklebust <Trond.Myklebust@primarydata.com>
---
 fs/nfs/delegation.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 7f3f60641344..02b5b2a6d557 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -301,6 +301,19 @@ nfs_inode_detach_delegation(struct inode *inode)
 	return nfs_detach_delegation(nfsi, delegation, server);
 }
 
+static void
+nfs_update_inplace_delegation(struct nfs_inode *nfsi,
+		struct nfs_delegation *delegation,
+		struct nfs_delegation *update)
+{
+	if (nfs4_stateid_is_newer(&update->stateid, &delegation->stateid))
+		return;
+	delegation->stateid.seqid = update->stateid.seqid;
+	smp_wmb();
+	delegation->type = update->type;
+	nfsi->delegation_state = update->type;
+}
+
 /**
  * nfs_inode_set_delegation - set up a delegation on an inode
  * @inode: inode to which delegation applies
@@ -334,9 +347,11 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 	old_delegation = rcu_dereference_protected(nfsi->delegation,
 					lockdep_is_held(&clp->cl_lock));
 	if (old_delegation != NULL) {
-		if (nfs4_stateid_match(&delegation->stateid,
-					&old_delegation->stateid) &&
-				delegation->type == old_delegation->type) {
+		/* Is this an update of the existing delegation? */
+		if (nfs4_stateid_match_other(&old_delegation->stateid,
+					&delegation->stateid)) {
+			nfs_update_inplace_delegation(nfsi, old_delegation,
+					delegation);
 			goto out;
 		}
 		/*
-- 
2.1.0