From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751567AbeFEBSl (ORCPT ); Mon, 4 Jun 2018 21:18:41 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:52298 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751170AbeFEBSk (ORCPT ); Mon, 4 Jun 2018 21:18:40 -0400 Date: Mon, 4 Jun 2018 18:18:36 -0700 From: Matthew Wilcox To: Naoya Horiguchi Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Michal Hocko , "mingo@kernel.org" , "dan.j.williams@intel.com" , Huang Ying Subject: Re: kernel panic in reading /proc/kpageflags when enabling RAM-simulated PMEM Message-ID: <20180605011836.GA32444@bombadil.infradead.org> References: <20180605005402.GA22975@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180605005402.GA22975@hori1.linux.bs1.fc.nec.co.jp> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 05, 2018 at 12:54:03AM +0000, Naoya Horiguchi wrote: > Reproduction precedure is like this: > - enable RAM based PMEM (with a kernel boot parameter like memmap=1G!4G) > - read /proc/kpageflags (or call tools/vm/page-types with no arguments) > (- my kernel config is attached) > > I spent a few days on this, but didn't reach any solutions. > So let me report this with some details below ... > > In the critial page request, stable_page_flags() is called with an argument > page whose ->compound_head was somehow filled with '0xffffffffffffffff'. > And compound_head() returns (struct page *)(head - 1), which explains the > address 0xfffffffffffffffe in the above message. Hm. compound_head shares with: struct list_head lru; struct list_head slab_list; /* uses lru */ struct { /* Partial pages */ struct page *next; unsigned long _compound_pad_1; /* compound_head */ unsigned long _pt_pad_1; /* compound_head */ struct dev_pagemap *pgmap; struct rcu_head rcu_head; None of them should be -1. > It seems that this kernel panic happens when reading kpageflags of pfn range > [0xbffd7, 0xc0000), which coresponds to a 'reserved' range. > > [ 0.000000] user-defined physical RAM map: > [ 0.000000] user: [mem 0x0000000000000000-0x000000000009fbff] usable > [ 0.000000] user: [mem 0x000000000009fc00-0x000000000009ffff] reserved > [ 0.000000] user: [mem 0x00000000000f0000-0x00000000000fffff] reserved > [ 0.000000] user: [mem 0x0000000000100000-0x00000000bffd6fff] usable > [ 0.000000] user: [mem 0x00000000bffd7000-0x00000000bfffffff] reserved > [ 0.000000] user: [mem 0x00000000feffc000-0x00000000feffffff] reserved > [ 0.000000] user: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved > [ 0.000000] user: [mem 0x0000000100000000-0x000000013fffffff] persistent (type 12) > > So I guess 'memmap=' parameter might badly affect the memory initialization process. > > This problem doesn't reproduce on v4.17, so some pre-released patch introduces it. > I hope this info helps you find the solution/workaround. Can you try bisecting this? It could be one of my patches to reorder struct page, or it could be one of Pavel's deferred page initialisation patches. Or something else ;-)