NFSv4: Use the open stateid if the delegation has the wrong mode

Fix nfs4_select_rw_stateid() so that it chooses the open stateid
(or an all-zero stateid) if the delegation does not match the selected
read/write mode.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4_fs.h

@@ -144,6 +144,7 @@ struct nfs4_lock_state {
 enum {
 	LK_STATE_IN_USE,
 	NFS_DELEGATED_STATE,		/* Current stateid is delegation */
+	NFS_OPEN_STATE,			/* OPEN stateid is set */
 	NFS_O_RDONLY_STATE,		/* OPEN stateid has read-only state */
 	NFS_O_WRONLY_STATE,		/* OPEN stateid has write-only state */
 	NFS_O_RDWR_STATE,		/* OPEN stateid has read/write state */

fs/nfs/nfs4proc.c

@@ -978,6 +978,7 @@ static void nfs_set_open_stateid_locked(struct nfs4_state *state, nfs4_stateid *
 	if (test_bit(NFS_DELEGATED_STATE, &state->flags) == 0)
 		nfs4_stateid_copy(&state->stateid, stateid);
 	nfs4_stateid_copy(&state->open_stateid, stateid);
+	set_bit(NFS_OPEN_STATE, &state->flags);
 	switch (fmode) {
 		case FMODE_READ:
 			set_bit(NFS_O_RDONLY_STATE, &state->flags);

fs/nfs/nfs4state.c

@@ -1024,12 +1024,16 @@ static int nfs4_copy_lock_stateid(nfs4_stateid *dst,
 
 static int nfs4_copy_open_stateid(nfs4_stateid *dst, struct nfs4_state *state)
 {
+	const nfs4_stateid *src;
 	int ret;
 	int seq;
 
 	do {
+		src = &zero_stateid;
 		seq = read_seqbegin(&state->seqlock);
-		nfs4_stateid_copy(dst, &state->stateid);
+		if (test_bit(NFS_OPEN_STATE, &state->flags))
+			src = &state->open_stateid;
+		nfs4_stateid_copy(dst, src);
 		ret = 0;
 		smp_rmb();
 		if (!list_empty(&state->owner->so_seqid.list))