From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f50.google.com (mail-wm0-f50.google.com [74.125.82.50]) by kanga.kvack.org (Postfix) with ESMTP id E9BDE6B025E for ; Tue, 29 Mar 2016 05:52:40 -0400 (EDT) Received: by mail-wm0-f50.google.com with SMTP id p65so18172335wmp.0 for ; Tue, 29 Mar 2016 02:52:40 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z193si15633963wme.98.2016.03.29.02.52.39 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 29 Mar 2016 02:52:39 -0700 (PDT) Subject: Re: [PATCH] mm: fix invalid node in alloc_migrate_target() References: <56F4E104.9090505@huawei.com> <20160325122237.4ca4e0dbca215ccbf4f49922@linux-foundation.org> <56F61EC8.7080508@huawei.com> From: Vlastimil Babka Message-ID: <56FA5062.2020103@suse.cz> Date: Tue, 29 Mar 2016 11:52:34 +0200 MIME-Version: 1.0 In-Reply-To: <56F61EC8.7080508@huawei.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Xishi Qiu , Andrew Morton Cc: Joonsoo Kim , David Rientjes , Naoya Horiguchi , Laura Abbott , zhuhui@xiaomi.com, wangxq10@lzu.edu.cn, Linux MM , LKML , Dave Hansen On 03/26/2016 06:31 AM, Xishi Qiu wrote: > On 2016/3/26 3:22, Andrew Morton wrote: > >> On Fri, 25 Mar 2016 14:56:04 +0800 Xishi Qiu wrote: >> >>> It is incorrect to use next_node to find a target node, it will >>> return MAX_NUMNODES or invalid node. This will lead to crash in >>> buddy system allocation. >>> >>> ... >>> >>> --- a/mm/page_isolation.c >>> +++ b/mm/page_isolation.c >>> @@ -289,11 +289,11 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private, >>> * now as a simple work-around, we use the next node for destination. >>> */ >>> if (PageHuge(page)) { >>> - nodemask_t src = nodemask_of_node(page_to_nid(page)); >>> - nodemask_t dst; >>> - nodes_complement(dst, src); >>> + int node = next_online_node(page_to_nid(page)); >>> + if (node == MAX_NUMNODES) >>> + node = first_online_node; >>> return alloc_huge_page_node(page_hstate(compound_head(page)), >>> - next_node(page_to_nid(page), dst)); >>> + node); >>> } >>> >>> if (PageHighMem(page)) >> >> Indeed. Can you tell us more about this circumstances under which the >> kernel will crash? I need to decide which kernel version(s) need the >> patch, but the changelog doesn't contain the info needed to make this >> decision (it should). >> > > Hi Andrew, > > I read the code v4.4, and find the following path maybe trigger the bug. > > alloc_migrate_target() > alloc_huge_page_node() // the node may be offline or MAX_NUMNODES > __alloc_buddy_huge_page_no_mpol() > __alloc_buddy_huge_page() > __hugetlb_alloc_buddy_huge_page() The code in this functions seems to come from 099730d67417d ("mm, hugetlb: use memory policy when available") by Dave Hansen (adding to CC), which was indeed merged in 4.4-rc1. However, alloc_pages_node() is only called in the block guarded by: if (!IS_ENABLED(CONFIG_NUMA) || !vma) { The rather weird "!IS_ENABLED(CONFIG_NUMA)" part comes from immediate followup commit e0ec90ee7e6f ("mm, hugetlbfs: optimize when NUMA=n") So I doubt the code path here can actually happen. But it's fragile and confusing nevertheless. > alloc_pages_node() > __alloc_pages_node() > VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); > VM_WARN_ON(!node_online(nid)); > > Thanks, > Xishi Qiu > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org