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,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 9DD23C46460 for ; Tue, 14 Aug 2018 09:39:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FE2A21735 for ; Tue, 14 Aug 2018 09:39:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FE2A21735 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 S1731452AbeHNM0C (ORCPT ); Tue, 14 Aug 2018 08:26:02 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:34674 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728272AbeHNM0C (ORCPT ); Tue, 14 Aug 2018 08:26:02 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7903B40203F2; Tue, 14 Aug 2018 09:39:37 +0000 (UTC) Received: from [10.36.117.57] (ovpn-117-57.ams2.redhat.com [10.36.117.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id DD7722156712; Tue, 14 Aug 2018 09:39:34 +0000 (UTC) Subject: Re: [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes To: osalvador@techadventures.net, akpm@linux-foundation.org Cc: mhocko@suse.com, dan.j.williams@intel.com, jglisse@redhat.com, rafael@kernel.org, yasu.isimatu@gmail.com, logang@deltatee.com, dave.jiang@intel.com, Jonathan.Cameron@huawei.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador References: <20180813154639.19454-1-osalvador@techadventures.net> <20180813154639.19454-4-osalvador@techadventures.net> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@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: <20180813154639.19454-4-osalvador@techadventures.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Tue, 14 Aug 2018 09:39:37 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Tue, 14 Aug 2018 09:39:37 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'david@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13.08.2018 17:46, osalvador@techadventures.net wrote: > From: Oscar Salvador > > unregister_mem_sect_under_nodes() tries to allocate a nodemask_t > in order to check whithin the loop which nodes have already been unlinked, > so we do not repeat the operation on them. > > NODEMASK_ALLOC calls kmalloc() if NODES_SHIFT > 8, otherwise > it just declares a nodemask_t variable whithin the stack. > > Since kamlloc() can fail, we actually check whether NODEMASK_ALLOC failed or > not, and we return -ENOMEM accordingly. > remove_memory_section() does not check for the return value though. > > The problem with this is that if we return -ENOMEM, it means that > unregister_mem_sect_under_nodes will not be able to remove the symlinks, > but since we do not check the return value, we go ahead and we call unregister_memory(), > which will remove all the mem_blks directories. > > This will leave us with dangled symlinks. > > The easiest way to overcome this is to fallback by calling sysfs_remove_link() > unconditionally in case NODEMASK_ALLOC failed. > This means that we will call sysfs_remove_link on nodes that have been already unlinked, > but nothing wrong happens as sysfs_remove_link() backs off somewhere down the chain in case > the link has already been removed. > > I think that this is better than > > a) dangled symlinks > b) having to recovery from such error in remove_memory_section > > Since from now on we will not need to take care about return values, we can make the function void. > > While at it, we can also drop the node_online() check, as a node can only be > offline if all the memory/cpus associated with it have been removed. I would prefer splitting this change out into a separate patch. > > As we have a safe fallback, one thing that could also be done is to add __GFP_NORETRY > in the flags when calling NODEMASK_ALLOC, so we do not retry. > > Signed-off-by: Oscar Salvador > --- > drivers/base/node.c | 26 +++++++++++++++----------- > include/linux/node.h | 5 ++--- > 2 files changed, 17 insertions(+), 14 deletions(-) > > diff --git a/drivers/base/node.c b/drivers/base/node.c > index dd3bdab230b2..0a3ca62687ea 100644 > --- a/drivers/base/node.c > +++ b/drivers/base/node.c > @@ -449,35 +449,39 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg) > } > > /* unregister memory section under all nodes that it spans */ > -int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > +void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > unsigned long phys_index) > { > NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); > unsigned long pfn, sect_start_pfn, sect_end_pfn; > > - if (!unlinked_nodes) > - return -ENOMEM; > - nodes_clear(*unlinked_nodes); > + if (unlinked_nodes) > + nodes_clear(*unlinked_nodes); > > sect_start_pfn = section_nr_to_pfn(phys_index); > sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1; > for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) { > - int nid; > + int nid = get_nid_for_pfn(pfn);; > > - nid = get_nid_for_pfn(pfn); > if (nid < 0) > continue; > - if (!node_online(nid)) > - continue; > - if (node_test_and_set(nid, *unlinked_nodes)) > + /* > + * It is possible that NODEMASK_ALLOC fails due to memory pressure. > + * If that happens, we fallback to call sysfs_remove_link unconditionally. > + * Nothing wrong will happen as sysfs_remove_link will back off > + * somewhere down the chain in case the link has already been removed. > + */ > + if (unlinked_nodes && node_test_and_set(nid, *unlinked_nodes)) > continue; > + > sysfs_remove_link(&node_devices[nid]->dev.kobj, > kobject_name(&mem_blk->dev.kobj)); > sysfs_remove_link(&mem_blk->dev.kobj, > kobject_name(&node_devices[nid]->dev.kobj)); > } > - NODEMASK_FREE(unlinked_nodes); > - return 0; > + > + if (unlinked_nodes) > + NODEMASK_FREE(unlinked_nodes); NODEMASK_FEEE/kfree can deal with NULL pointers. > } > > int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn) > diff --git a/include/linux/node.h b/include/linux/node.h > index 257bb3d6d014..1203378e596a 100644 > --- a/include/linux/node.h > +++ b/include/linux/node.h > @@ -72,7 +72,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid); > extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid); > extern int register_mem_sect_under_node(struct memory_block *mem_blk, > void *arg); > -extern int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > +extern void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > unsigned long phys_index); > > #ifdef CONFIG_HUGETLBFS > @@ -105,10 +105,9 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk, > { > return 0; > } > -static inline int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > +static inline void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > unsigned long phys_index) > { > - return 0; > } > > static inline void register_hugetlbfs_with_node(node_registration_func_t reg, > -- Thanks, David / dhildenb