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 63D34C07E85 for ; Wed, 5 Dec 2018 15:37:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27C05206B7 for ; Wed, 5 Dec 2018 15:37:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27C05206B7 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 S1728087AbeLEPhR convert rfc822-to-8bit (ORCPT ); Wed, 5 Dec 2018 10:37:17 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49998 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727337AbeLEPhQ (ORCPT ); Wed, 5 Dec 2018 10:37:16 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B896B3082143; Wed, 5 Dec 2018 15:37:15 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-55.bos.redhat.com [10.18.17.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id 817DE612A7; Wed, 5 Dec 2018 15:37:14 +0000 (UTC) Subject: Re: [PATCH 0/2] locking/lockdep: Track number of zapped classes & report abuse From: Waiman Long To: Peter Zijlstra Cc: Ingo Molnar , Will Deacon , Thomas Gleixner , linux-kernel@vger.kernel.org, Bart Van Assche References: <1543531297-18349-1-git-send-email-longman@redhat.com> <20181129224836.GI11632@hirez.programming.kicks-ass.net> <0c6c14e0-2c85-d4b7-bfa6-345cfae0d8b2@redhat.com> 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: <0c6c14e0-2c85-d4b7-bfa6-345cfae0d8b2@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 05 Dec 2018 15:37:15 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/30/2018 09:38 AM, Waiman Long wrote: > On 11/29/2018 05:48 PM, Peter Zijlstra wrote: >> On Thu, Nov 29, 2018 at 05:41:35PM -0500, Waiman Long wrote: >>> When a kernel module is repeatedly load and unload, it will eventually >>> exhaust the lockdep entries resulting in a bug message. This is a use >>> case that the current lockdep code cannot support. >>> >>> This patchset tracks the number of zapped classes and print a warning if >>> too many lockdep entries are wasted because of too many module unloading. >>> For example, >>> >>> [ 2490.651531] BUG: MAX_LOCKDEP_KEYS too low! >>> [ 2490.669925] turning off the locking correctness validator. >>> [ 2490.669925] Please attach the output of /proc/lock_stat to the bug report >>> [ 2490.669926] ======================================================== >>> [ 2490.669927] WARNING: 6499 out of 8191 locks have been destroyed >>> [ 2490.669927] through kernel module unload operations. >>> [ 2490.669928] The corresponding lockdep entries are not reusable. >>> [ 2490.669928] The system might have run out of lockdep entries because >>> [ 2490.669929] of repeated kernel module load and unload operations. >>> [ 2490.669929] Lockdep cannot support this particular use case. >>> [ 2490.669930] -------------------------------------------------------- >> Have a look here: >> >> https://lkml.kernel.org/r/20181128234325.110011-1-bvanassche@acm.org > Thanks for the pointer, I will take a look at that. > > Cheers, > Longman > I have finished reviewing Bart's v2 patch. It enables the reuse of lock_classes[] and list_entries[] entries. However, the stack_trace[], lock_chains[] and chain_hlocks[] entries will still be exhausted over time. So it doesn't completely solve the issue that I am looking at. As a side note, an alternative way of solving the workqueue lockdep problem may be to mark the lockdep key as special that it will hash the actual lock address as part of the key so that each unique lock of the same key will have its own unique lock class. That may be able to fix the issue as well. Just a thought. Cheers, Longman