From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 214606B000D for ; Mon, 2 Jul 2018 11:59:02 -0400 (EDT) Received: by mail-ed1-f71.google.com with SMTP id a22-v6so5920907eds.13 for ; Mon, 02 Jul 2018 08:59:02 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id y22-v6si3440207edr.193.2018.07.02.08.59.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Jul 2018 08:59:00 -0700 (PDT) Date: Mon, 2 Jul 2018 17:58:58 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: teach dump_page() to correctly output poisoned struct pages Message-ID: <20180702155858.GE19043@dhcp22.suse.cz> References: <20180702152745.27596-1-pasha.tatashin@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180702152745.27596-1-pasha.tatashin@oracle.com> Sender: owner-linux-mm@kvack.org List-ID: To: Pavel Tatashin Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mgorman@techsingularity.net, gregkh@linuxfoundation.org On Mon 02-07-18 11:27:45, Pavel Tatashin wrote: > If struct page is poisoned, and uninitialized access is detected via > PF_POISONED_CHECK(page) dump_page() is called to output the page. But, > the dump_page() itself accesses struct page to determine how to print > it, and therefore gets into a recursive loop. > > For example: > dump_page() > __dump_page() > PageSlab(page) > PF_POISONED_CHECK(page) > VM_BUG_ON_PGFLAGS(PagePoisoned(page), page) > dump_page() recursion loop. This deserves a big fat comment in __dump_page. Basically no Page$FOO can be used on an HWPoison page. > Fixes: f165b378bbdf ("mm: uninitialized struct page poisoning sanity checking") > Signed-off-by: Pavel Tatashin Acked-by: Michal Hocko > --- > mm/debug.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/mm/debug.c b/mm/debug.c > index 56e2d9125ea5..469b526e6abc 100644 > --- a/mm/debug.c > +++ b/mm/debug.c > @@ -43,12 +43,20 @@ const struct trace_print_flags vmaflag_names[] = { > > void __dump_page(struct page *page, const char *reason) > { > + bool page_poisoned = PagePoisoned(page); > + int mapcount; > + > + if (page_poisoned) { > + pr_emerg("page:%px is uninitialized and poisoned", page); > + goto hex_only; > + } > + > /* > * Avoid VM_BUG_ON() in page_mapcount(). > * page->_mapcount space in struct page is used by sl[aou]b pages to > * encode own info. > */ > - int mapcount = PageSlab(page) ? 0 : page_mapcount(page); > + mapcount = PageSlab(page) ? 0 : page_mapcount(page); > > pr_emerg("page:%px count:%d mapcount:%d mapping:%px index:%#lx", > page, page_ref_count(page), mapcount, > @@ -60,6 +68,7 @@ void __dump_page(struct page *page, const char *reason) > > pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags); > > +hex_only: > print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE, 32, > sizeof(unsigned long), page, > sizeof(struct page), false); > @@ -68,7 +77,7 @@ void __dump_page(struct page *page, const char *reason) > pr_alert("page dumped because: %s\n", reason); > > #ifdef CONFIG_MEMCG > - if (page->mem_cgroup) > + if (!page_poisoned && page->mem_cgroup) > pr_alert("page->mem_cgroup:%px\n", page->mem_cgroup); > #endif > } > -- > 2.18.0 > -- Michal Hocko SUSE Labs