From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 68047C43387 for ; Fri, 4 Jan 2019 18:37:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D411218DE for ; Fri, 4 Jan 2019 18:37:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727333AbfADShU (ORCPT ); Fri, 4 Jan 2019 13:37:20 -0500 Received: from foss.arm.com ([217.140.101.70]:48672 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726036AbfADShT (ORCPT ); Fri, 4 Jan 2019 13:37:19 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8069315AD; Fri, 4 Jan 2019 10:37:19 -0800 (PST) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.113]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 91BCD3F5D4; Fri, 4 Jan 2019 10:37:18 -0800 (PST) Date: Fri, 4 Jan 2019 18:37:16 +0000 From: Catalin Marinas To: zhe.he@windriver.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: kmemleak: Turn kmemleak_lock to spin lock and RCU primitives Message-ID: <20190104183715.GC187360@arrakis.emea.arm.com> References: <1546612153-451172-1-git-send-email-zhe.he@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1546612153-451172-1-git-send-email-zhe.he@windriver.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 04, 2019 at 10:29:13PM +0800, zhe.he@windriver.com wrote: > It's not necessary to keep consistency between readers and writers of > kmemleak_lock. RCU is more proper for this case. And in order to gain better > performance, we turn the reader locks to RCU read locks and writer locks to > normal spin locks. This won't work. > @@ -515,9 +515,7 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias) > struct kmemleak_object *object; > > rcu_read_lock(); > - read_lock_irqsave(&kmemleak_lock, flags); > object = lookup_object(ptr, alias); > - read_unlock_irqrestore(&kmemleak_lock, flags); The comment on lookup_object() states that the kmemleak_lock must be held. That's because we don't have an RCU-like mechanism for removing removing objects from the object_tree_root: > > /* check whether the object is still available */ > if (object && !get_object(object)) > @@ -537,13 +535,13 @@ static struct kmemleak_object *find_and_remove_object(unsigned long ptr, int ali > unsigned long flags; > struct kmemleak_object *object; > > - write_lock_irqsave(&kmemleak_lock, flags); > + spin_lock_irqsave(&kmemleak_lock, flags); > object = lookup_object(ptr, alias); > if (object) { > rb_erase(&object->rb_node, &object_tree_root); > list_del_rcu(&object->object_list); > } > - write_unlock_irqrestore(&kmemleak_lock, flags); > + spin_unlock_irqrestore(&kmemleak_lock, flags); So here, while list removal is RCU-safe, rb_erase() is not. If you have time to implement an rb_erase_rcu(), than we could reduce the locking in kmemleak. -- Catalin