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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 6BB3FC54FDB for ; Wed, 25 Mar 2020 07:14:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8AB972173E for ; Wed, 25 Mar 2020 07:06:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fG7rcdUE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727277AbgCYHGz (ORCPT ); Wed, 25 Mar 2020 03:06:55 -0400 Received: from us-smtp-delivery-74.mimecast.com ([216.205.24.74]:33427 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725815AbgCYHGz (ORCPT ); Wed, 25 Mar 2020 03:06:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585120013; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=DXe37XA0lfapO5Rb1aOqlNhUPIp3vNMLcAvl3Ef53Tg=; b=fG7rcdUESzzzhEOtlVTcfooXFD+Iur+eymIU7S9bldzVQoYCJiIx+MERBG/L41GUKAsj2F 4p0oSRWU0lQpNhgcimZvXCX3c532Br+42xJaTEm1jEqwxkKrfc4TdXX1PkJWBtedswTMXV fxB8yoPVCi97w4jzfJpwI4Mexf3vONQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-145-lr4m0wjzMhewtNCfl9Hs1w-1; Wed, 25 Mar 2020 03:06:49 -0400 X-MC-Unique: lr4m0wjzMhewtNCfl9Hs1w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1E8248017CC; Wed, 25 Mar 2020 07:06:48 +0000 (UTC) Received: from localhost (ovpn-12-88.pek2.redhat.com [10.72.12.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A43DE91D82; Wed, 25 Mar 2020 07:06:46 +0000 (UTC) Date: Wed, 25 Mar 2020 15:06:43 +0800 From: Baoquan He To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, Sachin Sant , dan.j.williams@intel.com Subject: Re: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check Message-ID: <20200325070643.GH3039@MiWiFi-R3L-srv> References: <20200325031914.107660-1-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200325031914.107660-1-aneesh.kumar@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote: > Fixes the below crash > > 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") > Cc: Baoquan He > Reported-by: Sachin Sant > Signed-off-by: Aneesh Kumar K.V Maybe add Sachin's Tested-by, Sachin has tested and confirmed this fix works. > --- > 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; Not sure if we should add checking in valid_section() or pfn_valid(), e.g check ms->usage validation too. Otherwise, this fix looks good to me. Reviewed-by: Baoquan He