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 8C340C35247 for ; Tue, 4 Feb 2020 16:12:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 608D121582 for ; Tue, 4 Feb 2020 16:12:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="L2Msm28d" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727427AbgBDQMV (ORCPT ); Tue, 4 Feb 2020 11:12:21 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:23721 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727317AbgBDQMV (ORCPT ); Tue, 4 Feb 2020 11:12:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580832740; 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=sOrQ7w5M+kp5LzSySUhZ3mTMSbQnOjGBnYt8dbqzsv8=; b=L2Msm28d3mNzz1Zun2sMVHRmJxbv1kq+zfIix7PbL7iZhB0/iwMhSZ4Ogqcbz1r/cGH8Q/ eRTitoe993Jj2hiFok9N3dqTLO+tvGtDcpHVPKQo4rP9k8G+wo63vcJwFXEIJf4Ji4XXK+ OuMHwoDkGeoCFkBUQUDJZ7U/HW15itE= 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-3-cwyy0IVcPMOMomfWx25bIw-1; Tue, 04 Feb 2020 11:12:15 -0500 X-MC-Unique: cwyy0IVcPMOMomfWx25bIw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5442ADB62; Tue, 4 Feb 2020 16:12:14 +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 B29AD81213; Tue, 4 Feb 2020 16:12:13 +0000 (UTC) Subject: Re: [PATCH v5 6/7] locking/lockdep: Reuse freed chain_hlocks entries To: Peter Zijlstra Cc: Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org, Bart Van Assche References: <20200203164147.17990-1-longman@redhat.com> <20200203164147.17990-7-longman@redhat.com> <20200204154236.GE14879@hirez.programming.kicks-ass.net> From: Waiman Long Organization: Red Hat Message-ID: Date: Tue, 4 Feb 2020 11:12:13 -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: <20200204154236.GE14879@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 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/4/20 10:42 AM, Peter Zijlstra wrote: > On Mon, Feb 03, 2020 at 11:41:46AM -0500, Waiman Long wrote: >> + /* >> + * We require a minimum of 2 (u16) entries to encode a freelist >> + * 'pointer'. >> + */ >> + req = max(req, 2); > > Would something simple like the below not avoid that whole 1 entry > 'chain' nonsense? > > It boots and passes the selftests, so it must be perfect :-) > > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -3163,7 +3163,7 @@ static int validate_chain(struct task_st > * (If lookup_chain_cache_add() return with 1 it acquires > * graph_lock for us) > */ > - if (!hlock->trylock && hlock->check && > + if (!chain_head && !hlock->trylock && hlock->check && > lookup_chain_cache_add(curr, hlock, chain_key)) { > /* > * Check whether last held lock: > Well, I think that will eliminate the 1-entry chains for the process context. However, we can still have 1-entry chain in the irq context, I think, as long as there are process context locks in front of it. I think this fix is still worthwhile as it will eliminate some of the 1-entry chains. Cheers, Longman