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Tue, 1 Nov 2022 07:54:24 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id /kKXEbDQYGMVFwAAMHmgww (envelope-from ); Tue, 01 Nov 2022 07:54:24 +0000 Date: Tue, 1 Nov 2022 08:54:23 +0100 From: Michal Hocko To: Zach O'Keefe Cc: Yang Shi , 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: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667289266; a=rsa-sha256; cv=none; b=ylvDWlEPt7OkCeq60VQx5OkY4Cy7PV2is5DDfpVZwIlm4DPjtotj0xRKqo82tM2dVoiGfF XoUfIuzOefVYE0krgUVWWwyvdJ/Ubs0nunCgoOMFs2L93yHUfL1uoDG3KBUGWxGcPXpAPG zVrvbZqmITCr3B9K6qjMBvx7BcpegUs= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=q4KcyPrs; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf05.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667289266; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=yXPEUXV/416Reg713Kd7mHOIawcGRYFkNyfM/5Mm2HY=; b=1MHBC90NHA2wYDfZeB69iwlbtqzjNzSE0ZbW5fKJrE+GTZ0ej9Buh//lJrKRWHuTWEUBPI YYC4z7yf5RvaHeKBV1g+qEjSyxncUEa+OESkfYCcz0rcd3zqy0Ii38fTxnyQb/TxmmtDwz XBKxsqP0eO1dM+o/+Adqpv6hVBhGwnw= X-Rspam-User: Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=q4KcyPrs; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf05.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Stat-Signature: dwjxo8zjwzn4kz3fwiwwhi3fwair5ds1 X-Rspamd-Queue-Id: CC1C810000B X-Rspamd-Server: rspam06 X-HE-Tag: 1667289265-510448 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. But the mere possibility of the hotplug race should be a sufficient ground to remove those WARN_ONs Thanks! -- Michal Hocko SUSE Labs