From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754865AbcKYOhP (ORCPT ); Fri, 25 Nov 2016 09:37:15 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:34851 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754265AbcKYOgd (ORCPT ); Fri, 25 Nov 2016 09:36:33 -0500 Date: Fri, 25 Nov 2016 17:15:56 +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: <20161125141556.GA12872@node.shutemov.name> References: <296bdd6b-5c9e-0fbc-8aa1-4e95d0aff031@suse.cz> <2ff6eee6-8828-821a-7dde-c2f68da697a5@suse.cz> <20161125130757.GC3439@node.shutemov.name> <2ff83214-70fe-741e-bf05-fe4a4073ec3e@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ff83214-70fe-741e-bf05-fe4a4073ec3e@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 03:08:10PM +0100, Vlastimil Babka wrote: > On 11/25/2016 02:07 PM, Kirill A. Shutemov wrote: > >> --- 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) ;) > > Ah, damnit, thanks. > > ----8<---- > From 08d2ee803567c13e3de7ce7e19338fe5286cc6b8 Mon Sep 17 00:00:00 2001 > From: Vlastimil Babka > Date: Fri, 25 Nov 2016 09:08:05 +0100 > Subject: [PATCH v3] 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 Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov