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Date: Mon, 4 Jun 2018 18:18:36 -0700 From: Matthew Wilcox <willy@...radead.org> To: Naoya Horiguchi <n-horiguchi@...jp.nec.com> Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...nel.org>, "mingo@...nel.org" <mingo@...nel.org>, "dan.j.williams@...el.com" <dan.j.williams@...el.com>, Huang Ying <ying.huang@...el.com> Subject: Re: kernel panic in reading /proc/kpageflags when enabling RAM-simulated PMEM 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 ;-)
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