NFS: Fix dentry revalidation on NFSv4 lookup

We need to ensure that inode and dentry revalidation occurs correctly
on reopen of a file that is already open. Currently, we can end up
not revalidating either in the case of NFSv4.0, due to the 'cached open'
path.
Let's fix that by ensuring that we only do cached open for the special
cases of open recovery and delegation return.
Reported-by: NStan Hu <stanhu@gmail.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4proc.c

@@ -1349,12 +1349,20 @@ static bool nfs4_mode_match_open_stateid(struct nfs4_state *state,
 	return false;
 }
 
-static int can_open_cached(struct nfs4_state *state, fmode_t mode, int open_mode)
+static int can_open_cached(struct nfs4_state *state, fmode_t mode,
+		int open_mode, enum open_claim_type4 claim)
 {
 	int ret = 0;
 
 	if (open_mode & (O_EXCL|O_TRUNC))
 		goto out;
+	switch (claim) {
+	case NFS4_OPEN_CLAIM_NULL:
+	case NFS4_OPEN_CLAIM_FH:
+		goto out;
+	default:
+		break;
+	}
 	switch (mode & (FMODE_READ|FMODE_WRITE)) {
 		case FMODE_READ:
 			ret |= test_bit(NFS_O_RDONLY_STATE, &state->flags) != 0
@@ -1747,7 +1755,7 @@ static struct nfs4_state *nfs4_try_open_cached(struct nfs4_opendata *opendata)
 
 	for (;;) {
 		spin_lock(&state->owner->so_lock);
-		if (can_open_cached(state, fmode, open_mode)) {
+		if (can_open_cached(state, fmode, open_mode, claim)) {
 			update_open_stateflags(state, fmode);
 			spin_unlock(&state->owner->so_lock);
 			goto out_return_state;
@@ -2294,7 +2302,8 @@ static void nfs4_open_prepare(struct rpc_task *task, void *calldata)
 	if (data->state != NULL) {
 		struct nfs_delegation *delegation;
 
-		if (can_open_cached(data->state, data->o_arg.fmode, data->o_arg.open_flags))
+		if (can_open_cached(data->state, data->o_arg.fmode,
+					data->o_arg.open_flags, claim))
 			goto out_no_action;
 		rcu_read_lock();
 		delegation = rcu_dereference(NFS_I(data->state->inode)->delegation);