From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 278746B0005 for ; Wed, 6 Jun 2018 05:07:21 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id k62-v6so3275047oiy.1 for ; Wed, 06 Jun 2018 02:07:21 -0700 (PDT) Received: from tyo161.gate.nec.co.jp (tyo161.gate.nec.co.jp. [114.179.232.161]) by mx.google.com with ESMTPS id 127-v6si9321454oie.236.2018.06.06.02.07.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Jun 2018 02:07:19 -0700 (PDT) From: Naoya Horiguchi Subject: Re: kernel panic in reading /proc/kpageflags when enabling RAM-simulated PMEM Date: Wed, 6 Jun 2018 09:06:30 +0000 Message-ID: <20180606090630.GA27065@hori1.linux.bs1.fc.nec.co.jp> References: <20180605005402.GA22975@hori1.linux.bs1.fc.nec.co.jp> <20180605011836.GA32444@bombadil.infradead.org> <20180605073500.GA23766@hori1.linux.bs1.fc.nec.co.jp> <20180606051624.GA16021@hori1.linux.bs1.fc.nec.co.jp> <20180606080408.GA31794@techadventures.net> <20180606085319.GA32052@techadventures.net> In-Reply-To: <20180606085319.GA32052@techadventures.net> Content-Language: ja-JP Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Oscar Salvador Cc: Matthew Wilcox , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Michal Hocko , "mingo@kernel.org" , "dan.j.williams@intel.com" , Huang Ying , Pavel Tatashin On Wed, Jun 06, 2018 at 10:53:19AM +0200, Oscar Salvador wrote: > On Wed, Jun 06, 2018 at 10:04:08AM +0200, Oscar Salvador wrote: > > On Wed, Jun 06, 2018 at 05:16:24AM +0000, Naoya Horiguchi wrote: > > > On Tue, Jun 05, 2018 at 07:35:01AM +0000, Horiguchi Naoya(=1B$BKY8}= =1B(B =1B$BD>Li=1B(B) wrote: > > > > On Mon, Jun 04, 2018 at 06:18:36PM -0700, Matthew Wilcox wrote: > > > > > 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 mem= map=3D1G!4G) > > > > > > - read /proc/kpageflags (or call tools/vm/page-types with no a= rguments) > > > > > > (- 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 '0xfffffffff= fffffff'. > > > > > > And compound_head() returns (struct page *)(head - 1), which ex= plains 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; /* compou= nd_head */ > > > > > unsigned long _pt_pad_1; /* compou= nd_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=3D' parameter might badly affect the memory = initialization process. > > > > > > > > > > > > This problem doesn't reproduce on v4.17, so some pre-released p= atch 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 reo= rder struct > > > > > page, or it could be one of Pavel's deferred page initialisation = patches. > > > > > Or something else ;-) > > > > > > > > Thank you for the comment. I'm trying bisecting now, let you know t= he result later. > > > > > > > > And I found that my statement "not reproduce on v4.17" was wrong (I= used > > > > different kvm guests, which made some different test condition and = misguided me), > > > > this seems an older (at least < 4.15) bug. > > > > > > (Cc: Pavel) > > > > > > Bisection showed that the following commit introduced this issue: > > > > > > commit f7f99100d8d95dbcf09e0216a143211e79418b9f > > > Author: Pavel Tatashin > > > Date: Wed Nov 15 17:36:44 2017 -0800 > > > > > > mm: stop zeroing memory during allocation in vmemmap > > > > > > This patch postpones struct page zeroing to later stage of memory ini= tialization. > > > My kernel config disabled CONFIG_DEFERRED_STRUCT_PAGE_INIT so two cal= lsites of > > > __init_single_page() were never reached. So in such case, struct page= s populated > > > by vmemmap_pte_populate() could be left uninitialized? > > > And I'm not sure yet how this issue becomes visible with memmap=3D se= tting. > > > > I think that this becomes visible because memmap=3Dx!y creates a persis= tent memory region: > > > > parse_memmap_one > > { > > ... > > } else if (*p =3D=3D '!') { > > start_at =3D memparse(p+1, &p); > > e820__range_add(start_at, mem_size, E820_TYPE_PRAM); > > ... > > } > > > > and this region it is not added neither in memblock.memory nor in membl= ock.reserved. > > Ranges in memblock.memory get zeroed in memmap_init_zone(), while membl= ock.reserved get zeroed > > in free_low_memory_core_early(): > > > > static unsigned long __init free_low_memory_core_early(void) > > { > > ... > > for_each_reserved_mem_region(i, &start, &end) > > reserve_bootmem_region(start, end); > > ... > > } > > > > > > Maybe I am mistaken, but I think that persistent memory regions should = be marked as reserved. > > A comment in do_mark_busy() suggests this: > > > > static bool __init do_mark_busy(enum e820_type type, struct resource *r= es) > > { > > > > ... > > /* > > * Treat persistent memory like device memory, i.e. reserve it > > * for exclusive use of a driver > > */ > > ... > > } > > > > > > I wonder if something like this could work and if so, if it is right (i= haven't tested it yet): > > > > diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c > > index 71c11ad5643e..3c9686ef74e5 100644 > > --- a/arch/x86/kernel/e820.c > > +++ b/arch/x86/kernel/e820.c > > @@ -1247,6 +1247,11 @@ void __init e820__memblock_setup(void) > > if (end !=3D (resource_size_t)end) > > continue; > > > > + if (entry->type =3D=3D E820_TYPE_PRAM || entry->type = =3D=3D E820_TYPE_PMEM) { > > + memblock_reserve(entry->addr, entry->size); > > + continue; > > + } > > + > > if (entry->type !=3D E820_TYPE_RAM && entry->type !=3D = E820_TYPE_RESERVED_KERN) > > continue; > > It does not seem to work, so the reasoning might be incorrect. Thank you for the comment. One note is that the memory region with "broken struct page" is a typical reserved region, not a pmem region. Strangely reading offset 0xbffd7 of /proc/kpageflags is OK if pmem region does not exist, but NG if pmem region= exists. Reading the offset like 0x100000 (on pmem region) does not cause the crash, so pmem region seems properly set up. [ 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 = =3D=3D=3D> "broken struct page" region [ 0.000000] user: [mem 0x00000000feffc000-0x00000000feffffff] reserved [ 0.000000] user: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved [ 0.000000] user: [mem 0x0000000100000000-0x000000013fffffff] persistent= (type 12) =3D> pmem region [ 0.000000] user: [mem 0x0000000140000000-0x000000023fffffff] usable Thanks, Naoya Horiguchi=