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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A7C9DC433E3 for ; Thu, 23 Jul 2020 13:29:44 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 269D520709 for ; Thu, 23 Jul 2020 13:29:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 269D520709 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BCCqQ742KzDrPG for ; Thu, 23 Jul 2020 23:29:38 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.ibm.com (client-ip=148.163.156.1; helo=mx0a-001b2d01.pphosted.com; envelope-from=nathanl@linux.ibm.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BCCmz6m0lzDr82 for ; Thu, 23 Jul 2020 23:27:31 +1000 (AEST) Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 06NCilBt119835; Thu, 23 Jul 2020 09:27:23 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 32faj39pyq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 23 Jul 2020 09:27:23 -0400 Received: from m0098396.ppops.net (m0098396.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 06NDPvDw097457; Thu, 23 Jul 2020 09:27:22 -0400 Received: from ppma02wdc.us.ibm.com (aa.5b.37a9.ip4.static.sl-reverse.com [169.55.91.170]) by mx0a-001b2d01.pphosted.com with ESMTP id 32faj39py6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 23 Jul 2020 09:27:22 -0400 Received: from pps.filterd (ppma02wdc.us.ibm.com [127.0.0.1]) by ppma02wdc.us.ibm.com (8.16.0.42/8.16.0.42) with SMTP id 06NDP43K024175; Thu, 23 Jul 2020 13:27:21 GMT Received: from b03cxnp07028.gho.boulder.ibm.com (b03cxnp07028.gho.boulder.ibm.com [9.17.130.15]) by ppma02wdc.us.ibm.com with ESMTP id 32brq9mj8j-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 23 Jul 2020 13:27:21 +0000 Received: from b03ledav003.gho.boulder.ibm.com (b03ledav003.gho.boulder.ibm.com [9.17.130.234]) by b03cxnp07028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 06NDRKwL52363680 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 23 Jul 2020 13:27:20 GMT Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 227BA6A04F; Thu, 23 Jul 2020 13:27:20 +0000 (GMT) Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DBFFE6A04D; Thu, 23 Jul 2020 13:27:19 +0000 (GMT) Received: from localhost (unknown [9.160.116.141]) by b03ledav003.gho.boulder.ibm.com (Postfix) with ESMTP; Thu, 23 Jul 2020 13:27:19 +0000 (GMT) From: Nathan Lynch To: Pingfan Liu Subject: Re: [PATCHv3 2/2] powerpc/pseries: update device tree before ejecting hotplug uevents In-Reply-To: <1595382730-10565-2-git-send-email-kernelfans@gmail.com> References: <1595382730-10565-1-git-send-email-kernelfans@gmail.com> <1595382730-10565-2-git-send-email-kernelfans@gmail.com> Date: Thu, 23 Jul 2020 08:27:18 -0500 Message-ID: <87imee1hvt.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-23_05:2020-07-23, 2020-07-23 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 suspectscore=7 phishscore=0 mlxlogscore=999 lowpriorityscore=0 mlxscore=0 clxscore=1011 spamscore=0 adultscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007230093 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: cheloha@linux.ibm.com, kexec@lists.infradead.org, ldufour@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, Hari Bathini Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Pingfan Liu writes: > A bug is observed on pseries by taking the following steps on rhel: > -1. drmgr -c mem -r -q 5 > -2. echo c > /proc/sysrq-trigger > > And then, the failure looks like: > kdump: saving to /sysroot//var/crash/127.0.0.1-2020-01-16-02:06:14/ > kdump: saving vmcore-dmesg.txt > kdump: saving vmcore-dmesg.txt complete > kdump: saving vmcore > Checking for memory holes : [ 0.0 %] / Checking for memory holes : [100.0 %] | Excluding unnecessary pages : [100.0 %] \ Copying data : [ 0.3 %] - eta: 38s[ 44.337636] hash-mmu: mm: Hashing failure ! EA=0x7fffba400000 access=0x8000000000000004 current=makedumpfile > [ 44.337663] hash-mmu: trap=0x300 vsid=0x13a109c ssize=1 base psize=2 psize 2 pte=0xc000000050000504 > [ 44.337677] hash-mmu: mm: Hashing failure ! EA=0x7fffba400000 access=0x8000000000000004 current=makedumpfile > [ 44.337692] hash-mmu: trap=0x300 vsid=0x13a109c ssize=1 base psize=2 psize 2 pte=0xc000000050000504 > [ 44.337708] makedumpfile[469]: unhandled signal 7 at 00007fffba400000 nip 00007fffbbc4d7fc lr 000000011356ca3c code 2 > [ 44.338548] Core dump to |/bin/false pipe failed > /lib/kdump-lib-initramfs.sh: line 98: 469 Bus error $CORE_COLLECTOR /proc/vmcore $_mp/$KDUMP_PATH/$HOST_IP-$DATEDIR/vmcore-incomplete > kdump: saving vmcore failed > > * Root cause * > After analyzing, it turns out that in the current implementation, > when hot-removing lmb, the KOBJ_REMOVE event ejects before the dt updating as > the code __remove_memory() comes before drmem_update_dt(). > So in kdump kernel, when read_from_oldmem() resorts to > pSeries_lpar_hpte_insert() to install hpte, but fails with -2 due to > non-exist pfn. And finally, low_hash_fault() raise SIGBUS to process, as it > can be observed "Bus error" > > From a viewpoint of listener and publisher, the publisher notifies the > listener before data is ready. This introduces a problem where udev > launches kexec-tools (due to KOBJ_REMOVE) and loads a stale dt before > updating. And in capture kernel, makedumpfile will access the memory based > on the stale dt info, and hit a SIGBUS error due to an un-existed lmb. > > * Fix * > In order to fix this issue, update dt before __remove_memory(), and > accordingly the same rule in hot-add path. > > This will introduce extra dt updating payload for each involved lmb when hotplug. > But it should be fine since drmem_update_dt() is memory based operation and > hotplug is not a hot path. This is great analysis but the performance implications of the change are grave. The add/remove paths here are already O(n) where n is the quantity of memory assigned to the LP, this change would make it O(n^2): dlpar_memory_add_by_count for_each_drmem_lmb <-- dlpar_add_lmb drmem_update_dt(_v1|_v2) for_each_drmem_lmb <-- Memory add/remove isn't a hot path but quadratic runtime complexity isn't acceptable. Its current performance is bad enough that I have internal bugs open on it. Not to mention we leak memory every time drmem_update_dt is called because we can't safely free device tree properties :-( Also note that this sort of reverts (fixes?) 063b8b1251fd ("powerpc/pseries/memory-hotplug: Only update DT once per memory DLPAR request").