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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 2A813C76191 for ; Fri, 26 Jul 2019 07:06:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 04AA52189F for ; Fri, 26 Jul 2019 07:06:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564124780; bh=E5hcRJjUln+Y6J7enPT4yz1TeyFg261iY7wVmgHXkUE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=I/Dam1p7aOh1PwF8V8nXSQ4bqEq/P51d/9HMi4JHpaQxggzugwAtPk/3qFwUKbVIg rcBF0zbgf04cOppG9QTK1P0TdIv7A8uBYoJ9ul/eWEDlmGeObLn0DnxRN0vwg20heS K8/JLq5jMKdeooq3Pv+jh2eBzR3H12zxnZ2TRhQs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726268AbfGZHGT (ORCPT ); Fri, 26 Jul 2019 03:06:19 -0400 Received: from mx2.suse.de ([195.135.220.15]:40562 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725869AbfGZHGS (ORCPT ); Fri, 26 Jul 2019 03:06:18 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 810CAB128; Fri, 26 Jul 2019 07:06:16 +0000 (UTC) Date: Fri, 26 Jul 2019 09:06:15 +0200 From: Michal Hocko To: Toshiki Fukasawa Cc: "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 Message-ID: <20190726070615.GB6142@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40b3078e-fb8b-87ef-5c4e-6321956cc940@vx.jp.nec.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 00 41 54 55 48 89 fd 53 48 8b 57 08 48 8b 1f 48 8d 42 ff 83 e2 01 48 0f 44 c7 <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: 0000000000000000 > >> [ 114.502009] RDX: 0000000000000001 RSI: 00007ffca13a7310 RDI: ffffd07489000000 > >> [ 114.502637] RBP: ffffd07489000000 R08: 0000000000000001 R09: 0000000000000000 > >> [ 114.503270] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000240000 > >> [ 114.503896] R13: 0000000000080000 R14: 00007ffca13a7310 R15: ffffa5e601a0ff08 > >> [ 114.504530] FS: 00007f0266c7f540(0000) GS:ffff962dbbac0000(0000) knlGS:0000000000000000 > >> [ 114.505245] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > >> [ 114.505754] CR2: fffffffffffffffe CR3: 000000023a204000 CR4: 00000000000006e0 > >> [ 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=linux-mm&m=152964792500739&w=2) > > > Isn't that a bug that should be addressed rather than paper over it like this? > > I'm not sure. What do you think, Dan? 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. -- Michal Hocko SUSE Labs