NFSv4: Replace state_owner->so_owner_id with an ida based allocator

We're unlikely to ever need more than 2^31 simultaneous open owners,
so let's replace the custom allocator with the generic ida allocator.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index a8a42a6..8472707 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -405,6 +405,7 @@
 	struct rb_node **p = &server->state_owners.rb_node,
 		       *parent = NULL;
 	struct nfs4_state_owner *sp;
+	int err;
 
 	while (*p != NULL) {
 		parent = *p;
@@ -421,8 +422,9 @@
 			return sp;
 		}
 	}
-	nfs_alloc_unique_id_locked(&server->openowner_id,
-					&new->so_owner_id, 1, 64);
+	err = ida_get_new(&server->openowner_id, &new->so_owner_id);
+	if (err)
+		return ERR_PTR(err);
 	rb_link_node(&new->so_server_node, parent, p);
 	rb_insert_color(&new->so_server_node, &server->state_owners);
 	return new;
@@ -435,7 +437,7 @@
 
 	if (!RB_EMPTY_NODE(&sp->so_server_node))
 		rb_erase(&sp->so_server_node, &server->state_owners);
-	nfs_free_unique_id(&server->openowner_id, &sp->so_owner_id);
+	ida_remove(&server->openowner_id, sp->so_owner_id);
 }
 
 /*
@@ -534,8 +536,13 @@
 	new = nfs4_alloc_state_owner(server, cred, gfp_flags);
 	if (new == NULL)
 		goto out;
-	sp = nfs4_insert_state_owner_locked(new);
-	spin_unlock(&clp->cl_lock);
+	do {
+		if (ida_pre_get(&server->openowner_id, gfp_flags) == 0)
+			break;
+		spin_lock(&clp->cl_lock);
+		sp = nfs4_insert_state_owner_locked(new);
+		spin_unlock(&clp->cl_lock);
+	} while (sp == ERR_PTR(-EAGAIN));
 	if (sp != new)
 		nfs4_free_state_owner(new);
 out: