From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-f70.google.com (mail-ot1-f70.google.com [209.85.210.70]) by kanga.kvack.org (Postfix) with ESMTP id 1DED06B0003 for ; Mon, 1 Oct 2018 19:20:42 -0400 (EDT) Received: by mail-ot1-f70.google.com with SMTP id e17-v6so76522otk.10 for ; Mon, 01 Oct 2018 16:20:42 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id z5-v6si6926827ota.254.2018.10.01.16.20.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 Oct 2018 16:20:40 -0700 (PDT) Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w91NIVrm086764 for ; Mon, 1 Oct 2018 19:20:39 -0400 Received: from e35.co.us.ibm.com (e35.co.us.ibm.com [32.97.110.153]) by mx0a-001b2d01.pphosted.com with ESMTP id 2murm7hnqk-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 01 Oct 2018 19:20:39 -0400 Received: from localhost by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 1 Oct 2018 17:20:38 -0600 Subject: Re: [PATCH] migration/mm: Add WARN_ON to try_offline_node References: <20181001185616.11427.35521.stgit@ltcalpine2-lp9.aus.stglabs.ibm.com> <20181001202724.GL18290@dhcp22.suse.cz> From: Tyrel Datwyler Date: Mon, 1 Oct 2018 16:20:30 -0700 MIME-Version: 1.0 In-Reply-To: <20181001202724.GL18290@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Michael Bringmann Cc: Thomas Falcon , Kees Cook , Mathieu Malaterre , linux-kernel@vger.kernel.org, Nicholas Piggin , Pavel Tatashin , linux-mm@kvack.org, Mauricio Faria de Oliveira , Juliet Kim , Thiago Jung Bauermann , Nathan Fontenot , Andrew Morton , YASUAKI ISHIMATSU , linuxppc-dev@lists.ozlabs.org, Dan Williams , Oscar Salvador On 10/01/2018 01:27 PM, Michal Hocko wrote: > On Mon 01-10-18 13:56:25, Michael Bringmann wrote: >> In some LPAR migration scenarios, device-tree modifications are >> made to the affinity of the memory in the system. For instance, >> it may occur that memory is installed to nodes 0,3 on a source >> system, and to nodes 0,2 on a target system. Node 2 may not >> have been initialized/allocated on the target system. >> >> After migration, if a RTAS PRRN memory remove is made to a >> memory block that was in node 3 on the source system, then >> try_offline_node tries to remove it from node 2 on the target. >> The NODE_DATA(2) block would not be initialized on the target, >> and there is no validation check in the current code to prevent >> the use of a NULL pointer. > > I am not familiar with ppc and the above doesn't really help me > much. Sorry about that. But from the above it is not clear to me whether > it is the caller which does something unexpected or the hotplug code > being not robust enough. From your changelog I would suggest the later > but why don't we see the same problem for other archs? Is this a problem > of unrolling a partial failure? > > dlpar_remove_lmb does the following > > nid = memory_add_physaddr_to_nid(lmb->base_addr); > > remove_memory(nid, lmb->base_addr, block_sz); > > /* Update memory regions for memory remove */ > memblock_remove(lmb->base_addr, block_sz); > > dlpar_remove_device_tree_lmb(lmb); > > Is the whole operation correct when remove_memory simply backs off > silently. Why don't we have to care about memblock resp > dlpar_remove_device_tree_lmb parts? In other words how come the physical > memory range is valid while the node association is not? > I think the issue here is a race between the LPM code updating affinity and PRRN events being processed. Does your other patch[1] not fix the issue? Or is it that the LPM affinity updates don't do any of the initialization/allocation you mentioned? -Tyrel [1] https://lore.kernel.org/linuxppc-dev/20181001185603.11373.61650.stgit@ltcalpine2-lp9.aus.stglabs.ibm.com/T/#u