From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43CBEC43331 for ; Thu, 26 Mar 2020 00:38:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1725620772 for ; Thu, 26 Mar 2020 00:38:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585183101; bh=6XqFnjUYEhgYgKKUjpg7puclVqjDqQbNalTX5nxwQgY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=KaqZHX5kqHN7Wtrd++i0nyC15LuiIbaN8HotxDP5xoM3+lqsvnIvty/sWEj0VSxsD SIbqF/yHRc+S96jpMHNsm4nnrz6VxmjBI9cnWjE5y6m0fGyCQfkOxv4Z0xgJ2+cHmz qPPDGizkhGRu9GUDfzMwqF6ltHDy+K4n6t2xTWwA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727607AbgCZAiU (ORCPT ); Wed, 25 Mar 2020 20:38:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:46972 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727536AbgCZAiT (ORCPT ); Wed, 25 Mar 2020 20:38:19 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 646662076A; Thu, 26 Mar 2020 00:38:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585183098; bh=6XqFnjUYEhgYgKKUjpg7puclVqjDqQbNalTX5nxwQgY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=LkRP/TuCvV8ytf1gA4MmhvMTASt5+4pAnSCE7CJfFgl9uBtcp4s9Z5vi7HCwsDRPe hWXbBD1FpaOcma18yZ2qXUkqTOEVSLGEYW5QCuWVEYkLn1MlbhE18FNkYdRfX3P9Ip 4QfgJjXRQgExK1cNskTvkONWL9dvptAIJuEuzrXg= Date: Wed, 25 Mar 2020 17:38:17 -0700 From: Andrew Morton To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, Baoquan He , Sachin Sant , Pankaj Gupta , David Hildenbrand , Michal Hocko , Wei Yang , Oscar Salvador , Mike Rapoport Subject: Re: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check Message-Id: <20200325173817.a63f20dd0ec618e063569e4a@linux-foundation.org> In-Reply-To: <20200325031914.107660-1-aneesh.kumar@linux.ibm.com> References: <20200325031914.107660-1-aneesh.kumar@linux.ibm.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 25 Mar 2020 08:49:14 +0530 "Aneesh Kumar K.V" wrote: > Fixes the below crash (cc's added) > BUG: Kernel NULL pointer dereference on read at 0x00000000 > Faulting instruction address: 0xc000000000c3447c > Oops: Kernel access of bad area, sig: 11 [#1] > LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries > CPU: 11 PID: 7519 Comm: lt-ndctl Not tainted 5.6.0-rc7-autotest #1 > ... > NIP [c000000000c3447c] vmemmap_populated+0x98/0xc0 > LR [c000000000088354] vmemmap_free+0x144/0x320 > Call Trace: > section_deactivate+0x220/0x240 > __remove_pages+0x118/0x170 > arch_remove_memory+0x3c/0x150 > memunmap_pages+0x1cc/0x2f0 > devm_action_release+0x30/0x50 > release_nodes+0x2f8/0x3e0 > device_release_driver_internal+0x168/0x270 > unbind_store+0x130/0x170 > drv_attr_store+0x44/0x60 > sysfs_kf_write+0x68/0x80 > kernfs_fop_write+0x100/0x290 > __vfs_write+0x3c/0x70 > vfs_write+0xcc/0x240 > ksys_write+0x7c/0x140 > system_call+0x5c/0x68 > > With commit: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > section_mem_map is set to NULL after depopulate_section_mem(). This > was done so that pfn_page() can work correctly with kernel config that disables > SPARSEMEM_VMEMMAP. With that config pfn_to_page does > > __section_mem_map_addr(__sec) + __pfn; > where > > static inline struct page *__section_mem_map_addr(struct mem_section *section) > { > unsigned long map = section->section_mem_map; > map &= SECTION_MAP_MASK; > return (struct page *)map; > } > > Now with SPASEMEM_VMEMAP enabled, mem_section->usage->subsection_map is used to > check the pfn validity (pfn_valid()). Since section_deactivate release > mem_section->usage if a section is fully deactivated, pfn_valid() check after > a subsection_deactivate cause a kernel crash. > > static inline int pfn_valid(unsigned long pfn) > { > ... > return early_section(ms) || pfn_section_valid(ms, pfn); > } > > where > > static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) > { > int idx = subsection_map_index(pfn); > > return test_bit(idx, ms->usage->subsection_map); > } > > Avoid this by clearing SECTION_HAS_MEM_MAP when mem_section->usage is freed. > > Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") d41e2f3bd546 had cc:stable, so I shall add cc:stable to this one as well. > Cc: Baoquan He > Reported-by: Sachin Sant > Signed-off-by: Aneesh Kumar K.V > --- > mm/sparse.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/sparse.c b/mm/sparse.c > index aadb7298dcef..3012d1f3771a 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -781,6 +781,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, > ms->usage = NULL; > } > memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr); > + /* Mark the section invalid */ > + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP; > } > > if (section_is_early && memmap)