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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7CC32C4332F for ; Wed, 2 Nov 2022 07:14:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230290AbiKBHOx (ORCPT ); Wed, 2 Nov 2022 03:14:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42278 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229850AbiKBHOr (ORCPT ); Wed, 2 Nov 2022 03:14:47 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8EF9622281 for ; Wed, 2 Nov 2022 00:14:46 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id B2C6122534; Wed, 2 Nov 2022 07:14:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1667373283; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=jMvkyOD/iIw47kZSZp1eUBVWVdFfgFKaj/rNagbS5/c=; b=jxGeTM6NGuyj141nn+PrSo61q4FdbRznlyDI0vhGizoXbJwp8IutWT/EhsbkRXuuGagznP SdvBzgU71oHAWWgsogoFO1+serdjOFS4IkjZa5jKV9u7PQTe83c2qBThC59P19xPxWwqSg kn7Rx7OkEzreLr/g8daLpyBPrOCliug= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 936FD139D3; Wed, 2 Nov 2022 07:14:43 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id sxkvIeMYYmNkYgAAMHmgww (envelope-from ); Wed, 02 Nov 2022 07:14:43 +0000 Date: Wed, 2 Nov 2022 08:14:42 +0100 From: Michal Hocko To: Yang Shi Cc: Zach O'Keefe , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: don't warn if the node is offlined Message-ID: References: <20221031183122.470962-1-shy828301@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 01-11-22 10:12:49, Yang Shi wrote: > On Tue, Nov 1, 2022 at 12:54 AM Michal Hocko wrote: > > > > On Mon 31-10-22 17:05:06, Zach O'Keefe wrote: > > > On Mon, Oct 31, 2022 at 3:08 PM Michal Hocko wrote: > > > > > > > > On Mon 31-10-22 11:31:22, Yang Shi wrote: > > > > > Syzbot reported the below splat: > > > > > > > > > > WARNING: CPU: 1 PID: 3646 at include/linux/gfp.h:221 __alloc_pages_node include/linux/gfp.h:221 [inline] > > > > > WARNING: CPU: 1 PID: 3646 at include/linux/gfp.h:221 hpage_collapse_alloc_page mm/khugepaged.c:807 [inline] > > > > > WARNING: CPU: 1 PID: 3646 at include/linux/gfp.h:221 alloc_charge_hpage+0x802/0xaa0 mm/khugepaged.c:963 > > > > > Modules linked in: > > > > > CPU: 1 PID: 3646 Comm: syz-executor210 Not tainted 6.1.0-rc1-syzkaller-00454-ga70385240892 #0 > > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022 > > > > > RIP: 0010:__alloc_pages_node include/linux/gfp.h:221 [inline] > > > > > RIP: 0010:hpage_collapse_alloc_page mm/khugepaged.c:807 [inline] > > > > > RIP: 0010:alloc_charge_hpage+0x802/0xaa0 mm/khugepaged.c:963 > > > > > Code: e5 01 4c 89 ee e8 6e f9 ae ff 4d 85 ed 0f 84 28 fc ff ff e8 70 fc ae ff 48 8d 6b ff 4c 8d 63 07 e9 16 fc ff ff e8 5e fc ae ff <0f> 0b e9 96 fa ff ff 41 bc 1a 00 00 00 e9 86 fd ff ff e8 47 fc ae > > > > > RSP: 0018:ffffc90003fdf7d8 EFLAGS: 00010293 > > > > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > > > > > RDX: ffff888077f457c0 RSI: ffffffff81cd8f42 RDI: 0000000000000001 > > > > > RBP: ffff888079388c0c R08: 0000000000000001 R09: 0000000000000000 > > > > > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > > > > > R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000 > > > > > FS: 00007f6b48ccf700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 > > > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > > > CR2: 00007f6b48a819f0 CR3: 00000000171e7000 CR4: 00000000003506e0 > > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > > > Call Trace: > > > > > > > > > > collapse_file+0x1ca/0x5780 mm/khugepaged.c:1715 > > > > > > > > This is quite weird, isn't it? alloc_charge_hpage is selecting the most > > > > busy node (as per collapse_control). How come this can be an offline > > > > node? Is a parallel memory hotplug happening? > > > > > > TBH -- I did not look closely at the syzbot reproducer (let alone > > > attempt to run it) and assumed this was the case. Taking a quick look, > > > at least memory hot remove is enabled: > > > > > > CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG=y > > > CONFIG_ARCH_ENABLE_MEMORY_HOTREMOVE=y > > > CONFIG_MEMORY_HOTPLUG=y > > > CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE=y > > > CONFIG_MEMORY_HOTREMOVE=y > > > > > > But looking at the C reproducer, I don't immediately see anywhere > > > where we offline nodes. I'll try to run this tomorrow to make sure I'm > > > not missing something real here. > > > > Looking slightly closer at hpage_collapse_scan_file I think that it is > > possible that xas_for_each simply doesn't find any entries in the page > > cache and with khugepaged_max_ptes_none == HPAGE_PMD_NR we can fall back > > to collapse_file even without any real entries. > > The khugepaged_max_ptes_none can't be HPAGE_PMD_NR, it must be <= > (HPAGE_PMD_NR - 1), but MADV_COLLAPSE does ignore it. OK, I see. > But a closer look at the code about how to pick up the preferred node, > there seems to be a corner case for MADV_COLLAPSE. > > The code tried to do some balance if several nodes have the same hit > record. Basically it does conceptually: > * If the target_node <= last_target_node, then iterate from > last_target_node + 1 to MAX_NUMNODES (1024 on default config) > * If the max_value == node_load[nid], then target_node = nid Correct > So assuming the system has 2 nodes, the target_node is 0 and the > last_target_node is 1, if MADV_COLLAPSE path is hit, then it may > return 2 for target_node, but it is actually not existing (offline), > so the warn is triggered. How can node_load[2] > 0 (IIUC max_value > 0 here) if the node is offline (other than a race with hotplug)? > The below patch should be able to fix it: > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index ea0d186bc9d4..d24405e6736b 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -787,7 +787,8 @@ static int hpage_collapse_find_target_node(struct > collapse_control *cc) > if (target_node <= cc->last_target_node) > for (nid = cc->last_target_node + 1; nid < MAX_NUMNODES; > nid++) > - if (max_value == cc->node_load[nid]) { > + if (node_online(nid) && > + max_value == cc->node_load[nid]) { > target_node = nid; > break; > } Node, this is equally racy. node_online might become false right after the check. -- Michal Hocko SUSE Labs