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=-3.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 BEC58C67839 for ; Thu, 13 Dec 2018 19:59:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8704220870 for ; Thu, 13 Dec 2018 19:59:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8704220870 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 S1728964AbeLMT7R (ORCPT ); Thu, 13 Dec 2018 14:59:17 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35528 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728252AbeLMT7R (ORCPT ); Thu, 13 Dec 2018 14:59:17 -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 4C8E64E920; Thu, 13 Dec 2018 19:59:16 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-223.bos.redhat.com [10.18.17.223]) by smtp.corp.redhat.com (Postfix) with ESMTP id C56B765922; Thu, 13 Dec 2018 19:59:14 +0000 (UTC) Subject: Re: [PATCH] debugobjects: Move printk out of db lock critical sections To: Sergey Senozhatsky Cc: Thomas Gleixner , Andrew Morton , linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Yang Shi , Arnd Bergmann , Dmitry Safonov References: <1544653694-27873-1-git-send-email-longman@redhat.com> <20181213020342.GA4860@jagdpanzerIV> 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: <20181213020342.GA4860@jagdpanzerIV> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 13 Dec 2018 19:59:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/12/2018 09:03 PM, Sergey Senozhatsky wrote: > On (12/12/18 17:28), Waiman Long wrote: >> The db->lock is a raw spinlock and so the lock hold time is supposed >> to be short. This will not be the case when printk() is being involved >> in some of the critical sections. In order to avoid the long hold time, >> in case some messages need to be printed, the debug_object_is_on_stack() >> and debug_print_object() calls are now moved out of those critical >> sections. >> >> Holding the db->lock while calling printk() may lead to deadlock if >> printk() somehow requires the allocation/freeing of debug object that >> happens to be in the same hash bucket or a circular lock dependency >> warning from lockdep as reported in https://lkml.org/lkml/2018/12/11/143. >> >> [ 87.209665] WARNING: possible circular locking dependency detected >> [ 87.210547] 4.20.0-rc4-00057-gc96cf92 #1 Tainted: G W >> [ 87.211449] ------------------------------------------------------ >> [ 87.212405] getty/519 is trying to acquire lock: >> [ 87.213074] (____ptrval____) (&obj_hash[i].lock){-.-.}, at: debug_check_no_obj_freed+0xb4/0x302 >> [ 87.214343] >> [ 87.214343] but task is already holding lock: >> [ 87.215174] (____ptrval____) (&port_lock_key){-.-.}, at: uart_shutdown+0x3a3/0x4e2 >> [ 87.216260] >> [ 87.216260] which lock already depends on the new lock. >> >> This patch was also found to be able to fix a boot hanging problem >> when the initramfs image was switched on after a debugobjects splat >> from the EFI code. >> >> Signed-off-by: Waiman Long > The patch looks good to me. A bit curious if we need to also patch > the self-test part debugobjects - check_results(). That guy still > printk()-s under bucket ->lock. > > -ss Yes, I should have changed those in the check_results() as well. -Longman