There might be a potential race condition for the NFSv4 client

when a newly created file has another open done on it that
update the open mode. This patch moves the code that updates
the open mode up into the block where the mutex is held to
ensure this cannot happen. No bug caused by this potential
race has been observed, but this fix is a safety belt to ensure
it cannot happen.

MFC after:	2 weeks

sys/fs/nfsclient/nfs_clstate.c

@@ -280,6 +280,23 @@ nfscl_open(vnode_t vp, u_int8_t *nfhp, int fhlen, u_int32_t amode, int usedeleg,
 	nfscl_newopen(clp, dp, &owp, &nowp, &op, &nop, own, nfhp, fhlen,
 	    newonep);
 
+	/*
+	 * Now, check the mode on the open and return the appropriate
+	 * value.
+	 */
+	if (retp != NULL) {
+		if (nfhp != NULL && dp != NULL && nop == NULL)
+			/* new local open on delegation */
+			*retp = NFSCLOPEN_SETCRED;
+		else
+			*retp = NFSCLOPEN_OK;
+	}
+	if (op != NULL && (amode & ~(op->nfso_mode))) {
+		op->nfso_mode |= amode;
+		if (retp != NULL && dp == NULL)
+			*retp = NFSCLOPEN_DOOPEN;
+	}
+
 	/*
 	 * Serialize modifications to the open owner for multiple threads
 	 * within the same process using a read/write sleep lock.
@@ -295,23 +312,6 @@ nfscl_open(vnode_t vp, u_int8_t *nfhp, int fhlen, u_int32_t amode, int usedeleg,
 		*owpp = owp;
 	if (opp != NULL)
 		*opp = op;
-	if (retp != NULL) {
-		if (nfhp != NULL && dp != NULL && nop == NULL)
-			/* new local open on delegation */
-			*retp = NFSCLOPEN_SETCRED;
-		else
-			*retp = NFSCLOPEN_OK;
-	}
-
-	/*
-	 * Now, check the mode on the open and return the appropriate
-	 * value.
-	 */
-	if (op != NULL && (amode & ~(op->nfso_mode))) {
-		op->nfso_mode |= amode;
-		if (retp != NULL && dp == NULL)
-			*retp = NFSCLOPEN_DOOPEN;
-	}
 	return (0);
 }