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[114.179.232.162]) by mx.google.com with ESMTPS id h18si8570017ioj.95.2019.08.04.22.31.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 04 Aug 2019 22:31:23 -0700 (PDT) Received-SPF: pass (google.com: domain of t-fukasawa@vx.jp.nec.com designates 114.179.232.162 as permitted sender) client-ip=114.179.232.162; Authentication-Results: mx.google.com; spf=pass (google.com: domain of t-fukasawa@vx.jp.nec.com designates 114.179.232.162 as permitted sender) smtp.mailfrom=t-fukasawa@vx.jp.nec.com Received: from mailgate01.nec.co.jp ([114.179.233.122]) by tyo162.gate.nec.co.jp (8.15.1/8.15.1) with ESMTPS id x755V8XK004238 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Mon, 5 Aug 2019 14:31:08 +0900 Received: from mailsv01.nec.co.jp (mailgate-v.nec.co.jp [10.204.236.94]) by mailgate01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x755V8sK019089; Mon, 5 Aug 2019 14:31:08 +0900 Received: from mail03.kamome.nec.co.jp (mail03.kamome.nec.co.jp [10.25.43.7]) by mailsv01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x755M4TE002674; Mon, 5 Aug 2019 14:31:08 +0900 Received: from bpxc99gp.gisp.nec.co.jp ([10.38.151.152] [10.38.151.152]) by mail02.kamome.nec.co.jp with ESMTP id BT-MMP-7394443; Mon, 5 Aug 2019 14:12:41 +0900 Received: from BPXM20GP.gisp.nec.co.jp ([10.38.151.212]) by BPXC24GP.gisp.nec.co.jp ([10.38.151.152]) with mapi id 14.03.0439.000; Mon, 5 Aug 2019 14:12:41 +0900 From: Toshiki Fukasawa To: Michal Hocko CC: Toshiki Fukasawa , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "dan.j.williams@intel.com" , "adobriyan@gmail.com" , "hch@lst.de" , Naoya Horiguchi , Junichi Nomura , "stable@vger.kernel.org" Subject: Re: [PATCH 2/2] /proc/kpageflags: do not use uninitialized struct pages Thread-Topic: [PATCH 2/2] /proc/kpageflags: do not use uninitialized struct pages Thread-Index: AQHVQpEKFGt+j6P+NkKoSe72QQuzoKbac7OAgAFmX4CAAAsmgIAPl5OA Date: Mon, 5 Aug 2019 05:12:40 +0000 Message-ID: <3a926ce5-75b9-ea94-d6e4-6888872e0dc4@vx.jp.nec.com> References: <20190725023100.31141-1-t-fukasawa@vx.jp.nec.com> <20190725023100.31141-3-t-fukasawa@vx.jp.nec.com> <20190725090341.GC13855@dhcp22.suse.cz> <40b3078e-fb8b-87ef-5c4e-6321956cc940@vx.jp.nec.com> <20190726070615.GB6142@dhcp22.suse.cz> In-Reply-To: <20190726070615.GB6142@dhcp22.suse.cz> Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.178.21.43] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <092F480E631D4C46AA067F5ECBA30C88@gisp.nec.co.jp> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-TM-AS-MML: disable 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 2019/07/26 16:06, Michal Hocko wrote: > On Fri 26-07-19 06:25:49, Toshiki Fukasawa wrote: >> >> >> On 2019/07/25 18:03, Michal Hocko wrote: >>> On Thu 25-07-19 02:31:18, Toshiki Fukasawa wrote: >>>> A kernel panic was observed during reading /proc/kpageflags for >>>> first few pfns allocated by pmem namespace: >>>> >>>> BUG: unable to handle page fault for address: fffffffffffffffe >>>> [ 114.495280] #PF: supervisor read access in kernel mode >>>> [ 114.495738] #PF: error_code(0x0000) - not-present page >>>> [ 114.496203] PGD 17120e067 P4D 17120e067 PUD 171210067 PMD 0 >>>> [ 114.496713] Oops: 0000 [#1] SMP PTI >>>> [ 114.497037] CPU: 9 PID: 1202 Comm: page-types Not tainted 5.3.0-rc1= #1 >>>> [ 114.497621] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), = BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014 >>>> [ 114.498706] RIP: 0010:stable_page_flags+0x27/0x3f0 >>>> [ 114.499142] Code: 82 66 90 66 66 66 66 90 48 85 ff 0f 84 d1 03 00 0= 0 41 54 55 48 89 fd 53 48 8b 57 08 48 8b 1f 48 8d 42 ff 83 e2 01 48 0f 44 c= 7 <48> 8b 00 f6 c4 02 0f 84 57 03 00 00 45 31 e4 48 8b 55 08 48 89 ef >>>> [ 114.500788] RSP: 0018:ffffa5e601a0fe60 EFLAGS: 00010202 >>>> [ 114.501373] RAX: fffffffffffffffe RBX: ffffffffffffffff RCX: 000000= 0000000000 >>>> [ 114.502009] RDX: 0000000000000001 RSI: 00007ffca13a7310 RDI: ffffd0= 7489000000 >>>> [ 114.502637] RBP: ffffd07489000000 R08: 0000000000000001 R09: 000000= 0000000000 >>>> [ 114.503270] R10: 0000000000000000 R11: 0000000000000000 R12: 000000= 0000240000 >>>> [ 114.503896] R13: 0000000000080000 R14: 00007ffca13a7310 R15: ffffa5= e601a0ff08 >>>> [ 114.504530] FS: 00007f0266c7f540(0000) GS:ffff962dbbac0000(0000) k= nlGS:0000000000000000 >>>> [ 114.505245] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>> [ 114.505754] CR2: fffffffffffffffe CR3: 000000023a204000 CR4: 000000= 00000006e0 >>>> [ 114.506401] Call Trace: >>>> [ 114.506660] kpageflags_read+0xb1/0x130 >>>> [ 114.507051] proc_reg_read+0x39/0x60 >>>> [ 114.507387] vfs_read+0x8a/0x140 >>>> [ 114.507686] ksys_pread64+0x61/0xa0 >>>> [ 114.508021] do_syscall_64+0x5f/0x1a0 >>>> [ 114.508372] entry_SYSCALL_64_after_hwframe+0x44/0xa9 >>>> [ 114.508844] RIP: 0033:0x7f0266ba426b >>>> >>>> The reason for the panic is that stable_page_flags() which parses >>>> the page flags uses uninitialized struct pages reserved by the >>>> ZONE_DEVICE driver. >>> >>> Why pmem hasn't initialized struct pages? >> >> We proposed to initialize in previous approach but that wasn't merged. >> (See https://marc.info/?l=3Dlinux-mm&m=3D152964792500739&w=3D2) >> >>> Isn't that a bug that should be addressed rather than paper over it lik= e this? >> >> I'm not sure. What do you think, Dan? >=20 > Yeah, I am really curious about details. Why do we keep uninitialized > struct pages at all? What is a random pfn walker supposed to do? What > kind of metadata would be clobbered? In other words much more details > please. >=20 I also want to know. I do not think that initializing struct pages will clobber any metadata. Best regards, Toshiki Fukasawa=