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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 74EFDC43441 for ; Thu, 22 Nov 2018 20:17:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C5C22087E for ; Thu, 22 Nov 2018 20:17:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2C5C22087E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392841AbeKWG6y convert rfc822-to-8bit (ORCPT ); Fri, 23 Nov 2018 01:58:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46450 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392685AbeKWG6x (ORCPT ); Fri, 23 Nov 2018 01:58:53 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D63DF307D91C; Thu, 22 Nov 2018 20:17:55 +0000 (UTC) Received: from llong.remote.csb (ovpn-121-14.rdu2.redhat.com [10.10.121.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id 109FB1001F4A; Thu, 22 Nov 2018 20:17:53 +0000 (UTC) Subject: Re: [PATCH v2 09/17] debugobjects: Make object hash locks nestable terminal locks To: Petr Mladek Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Thomas Gleixner , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Sergey Senozhatsky , Andrey Ryabinin , Tejun Heo , Andrew Morton References: <1542653726-5655-1-git-send-email-longman@redhat.com> <1542653726-5655-10-git-send-email-longman@redhat.com> <20181122153302.y5vqovrsaigi6pte@pathway.suse.cz> From: Waiman Long Openpgp: preference=signencrypt Autocrypt: addr=longman@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181122153302.y5vqovrsaigi6pte@pathway.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Thu, 22 Nov 2018 20:17:56 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/22/2018 10:33 AM, Petr Mladek wrote: > On Mon 2018-11-19 13:55:18, Waiman Long wrote: >> By making the object hash locks nestable terminal locks, we can avoid >> a bunch of unnecessary lockdep validations as well as saving space >> in the lockdep tables. > Please, explain which terminal lock might be nested. > > Hmm, it would hide eventual nesting of other terminal locks. > It might reduce lockdep reliability. I wonder if the space > optimization is worth it. > > Finally, it might be good to add a short explanation what (nested) > terminal locks mean into each commit. It would help people to > understand the effect without digging into the lockdep code, ... > > Best Regards, > Petr Nested terminal lock is currently only used in the debugobjects code. It should only be used on a case-by-case basis. In the case of the debugojects code, the locking patterns are: (1) raw_spin_lock(&db_lock); ... raw_spin_unlock(&db_lock); (2) raw_spin_lock(&db_lock); ... raw_spin_lock(&pool_lock); ... raw_spin_unlock(&pool_lock); ... raw_spin_unlock(&db_lock); (3) raw_spin_lock(&pool_lock); ... raw_spin_unlock(&pool_lock); So the db_lock is made to be nestable that it can allow acquisition of pool_lock (a regular terminal lock) underneath it. Cheers, Longman