From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754653AbcKYN2a (ORCPT ); Fri, 25 Nov 2016 08:28:30 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:34304 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753556AbcKYN1e (ORCPT ); Fri, 25 Nov 2016 08:27:34 -0500 Date: Fri, 25 Nov 2016 16:07:57 +0300 From: "Kirill A. Shutemov" To: Vlastimil Babka Cc: Andrey Ryabinin , Dmitry Vyukov , Andrew Morton , "Kirill A. Shutemov" , Michal Hocko , Ingo Molnar , Joonsoo Kim , "linux-mm@kvack.org" , LKML , syzkaller Subject: Re: mm: BUG in pgtable_pmd_page_dtor Message-ID: <20161125130757.GC3439@node.shutemov.name> References: <296bdd6b-5c9e-0fbc-8aa1-4e95d0aff031@suse.cz> <2ff6eee6-8828-821a-7dde-c2f68da697a5@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ff6eee6-8828-821a-7dde-c2f68da697a5@suse.cz> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 25, 2016 at 01:58:57PM +0100, Vlastimil Babka wrote: > On 11/25/2016 12:41 PM, Andrey Ryabinin wrote: > > > > > > On 11/25/2016 11:42 AM, Vlastimil Babka wrote: > > > >> pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx", > >> page, page_ref_count(page), mapcount, > >> @@ -59,6 +61,21 @@ void __dump_page(struct page *page, const char *reason) > >> > >> pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags); > >> > >> + pr_alert("raw struct page data:"); > >> + for (i = 0; i < sizeof(struct page) / sizeof(unsigned long); i++) { > >> + unsigned long *word_ptr; > >> + > >> + word_ptr = ((unsigned long *) page) + i; > >> + > >> + if ((i % words_per_line) == 0) { > >> + pr_cont("\n"); > >> + pr_alert(" %016lx", *word_ptr); > >> + } else { > >> + pr_cont(" %016lx", *word_ptr); > >> + } > >> + } > >> + pr_cont("\n"); > >> + > > > > Single call to print_hex_dump() could replace this loop. > > Ah, didn't know about that one, thanks! > > This also addresses Kirill's comment: > > -----8<----- > From 417467521d0a68fb70dc2d5bd151524bf0c79437 Mon Sep 17 00:00:00 2001 > From: Vlastimil Babka > Date: Fri, 25 Nov 2016 09:08:05 +0100 > Subject: [PATCH] mm, debug: print raw struct page data in __dump_page() > > The __dump_page() function is used when a page metadata inconsistency is > detected, either by standard runtime checks, or extra checks in CONFIG_DEBUG_VM > builds. It prints some of the relevant metadata, but not the whole struct page, > which is based on unions and interpretation is dependent on the context. > > This means that sometimes e.g. a VM_BUG_ON_PAGE() checks certain field, which > is however not printed by __dump_page() and the resulting bug report may then > lack clues that could help in determining the root cause. This patch solves > the problem by simply printing the whole struct page word by word, so no part > is missing, but the interpretation of the data is left to developers. This is > similar to e.g. x86_64 raw stack dumps. > > Example output: > > page:ffffea00000475c0 count:1 mapcount:0 mapping: (null) index:0x0 > flags: 0x100000000000400(reserved) > raw: 0100000000000400 0000000000000000 0000000000000000 00000001ffffffff > raw: ffffea00000475e0 ffffea00000475e0 0000000000000000 0000000000000000 > page dumped because: VM_BUG_ON_PAGE(1) > > [aryabinin@virtuozzo.com: suggested print_hex_dump()] > Signed-off-by: Vlastimil Babka > --- > mm/debug.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/debug.c b/mm/debug.c > index 9feb699c5d25..185c19bda078 100644 > --- a/mm/debug.c > +++ b/mm/debug.c > @@ -59,6 +59,10 @@ void __dump_page(struct page *page, const char *reason) > > pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags); > > + print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE, > + 32, (sizeof(unsigned long) == 8) ? 8 : 4, That's a very fancy way to write sizeof(unsigned long) ;) -- Kirill A. Shutemov