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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 8390EC33CA9 for ; Mon, 13 Jan 2020 15:44:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F76C2081E for ; Mon, 13 Jan 2020 15:44:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bfiUEyQf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728688AbgAMPom (ORCPT ); Mon, 13 Jan 2020 10:44:42 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:52233 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726943AbgAMPom (ORCPT ); Mon, 13 Jan 2020 10:44:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578930280; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=baGQEJFe1m8uz44ROty+5bEDcZTrF/M70P1MM+fc8Tk=; b=bfiUEyQfTAy6VDAmrhPbCQjh97mwehBTxiEZSYsiAz90+iXoxKOxd/7PO7OguEmYKFkpZi Hi50e14eAYzjtujbrvokcF8+ycX6r0t8c3nd3cS/sD7zKiTRzFYx5+KvHHWfI3y0V3y9tD LVwZULKIBvHp80JMeBJMR+6QaKefBQI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-288-aKv1uNXONtiWhRNB4C5uNw-1; Mon, 13 Jan 2020 10:44:39 -0500 X-MC-Unique: aKv1uNXONtiWhRNB4C5uNw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3BBAD19586C4; Mon, 13 Jan 2020 15:44:38 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-59.bos.redhat.com [10.18.17.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9F6F55C1B0; Mon, 13 Jan 2020 15:44:37 +0000 (UTC) Subject: Re: [PATCH v2 2/6] locking/lockdep: Throw away all lock chains with zapped class To: Peter Zijlstra Cc: Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org, Bart Van Assche References: <20191216151517.7060-1-longman@redhat.com> <20191216151517.7060-3-longman@redhat.com> <20200113151806.GW2844@hirez.programming.kicks-ass.net> From: Waiman Long Organization: Red Hat Message-ID: <2c742217-fa18-bf87-2c0d-2c7f95887646@redhat.com> Date: Mon, 13 Jan 2020 10:44:37 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20200113151806.GW2844@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/13/20 10:18 AM, Peter Zijlstra wrote: > On Mon, Dec 16, 2019 at 10:15:13AM -0500, Waiman Long wrote: >> If a lock chain contains a class that is zapped, the whole lock chain is >> now invalid. > Possibly. But I'm thinking that argument can/should be made mode elaborate. > > Suppose we have A->B->C, and we're about to remove B. > > Now, I suppose the trivial argument goes that if we remove the text that > causes A->B, then so B->C will no longer happen. However, that doesn't > mean A->C won't still occur. > > OTOH, we might already have A->C and so our resulting chain would be a > duplicate. Conversely, if we didn't already have A->C and it does indeed > still occur (say it was omitted due to the redundant logic), then we > will create this dependency the next time we'll encounter it. I will prefer having it only when it actually happens rather than leaving a partial chain behind assuming that it may happen. > > Bart, do you see a problem with this reasoning? > > In short, yes, I think you're right and we can remove the whole thing. > But please, expand the Changelog a bit, possibly add some of this > reasoning into a comment. > Yes, I will elaborate more in the changelog. Cheers, Longman