[PATCH] exp_parent locking fixes

From: Neil Brown and myself.

Don't do dput() inside read_lock().  It can sleep.

fs/nfsd/export.c

@@ -543,13 +543,13 @@ exp_parent(svc_client *clp, struct vfsmount *mnt, struct dentry *dentry,
 	dget(dentry);
 	exp = exp_get_by_name(clp, mnt, dentry, reqp);
 
-	while (exp == NULL && dentry != dentry->d_parent) {
+	while (exp == NULL && !IS_ROOT(dentry)) {
 		struct dentry *parent;
 		read_lock(&dparent_lock);
 		parent = dget(dentry->d_parent);
+		read_unlock(&dparent_lock);
 		dput(dentry);
 		dentry = parent;
-		read_unlock(&dparent_lock);
 		exp = exp_get_by_name(clp, mnt, dentry, reqp);
 	}
 	dput(dentry);