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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 B0876C2D0E8 for ; Thu, 26 Mar 2020 09:40:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 84BCD20748 for ; Thu, 26 Mar 2020 09:40:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585215629; bh=Z28Ev0IOZSSfjf1lF/BxnvKMnUs3GW+iQDPOom5szFE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Ici0VY3tdWUUAHnHwAJDshTm7/66/8y4Dmtohwt2DYcGU1NS2WjILTTu6KhliYlUF 6qZOiLSdCgVRPGcSdFdEzgYgYS5XKraHVi5///HarmioF0KboPO7X6ac+D1xq9O/rQ 9lpIWuooH27NJx61aeMVvMRn8cDn+WKRp0lgF+50= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727842AbgCZJk1 (ORCPT ); Thu, 26 Mar 2020 05:40:27 -0400 Received: from mail-wr1-f68.google.com ([209.85.221.68]:37782 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727699AbgCZJk1 (ORCPT ); Thu, 26 Mar 2020 05:40:27 -0400 Received: by mail-wr1-f68.google.com with SMTP id w10so6887465wrm.4 for ; Thu, 26 Mar 2020 02:40:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=P7rfDvLouiYZHycnMC+LD8xViPsWvfdlRtaj/g8XMpI=; b=Bi3T4wxefdAYRJpvk5s2RJrGaIgqNdJg5JHTTG8E5j8X2OJnJPeKGO/emK9kWDoQ+s Iye2KlZgGIbl+QTrb9Is/sKgcBqF7u2dzgyGrGh00NbNx6l8Wy3qdIpVMwrDp/d/OCyf Jx6cU5BH5WeQKzP5w5tB8xucK35wGDJaVfNZBDYZJHUfC5yaEHpVXHMetMPwbStedGvq vKI7UkHvNKCf5Zz9FQXRK6QtMOXAMdaf0RfSO/vP+c0Njz8/qcGKF+bnIaQotyvDwzd5 kLcEhs0vsZqAzQsvhvqs9Q5fzEIGVYYKR8on0/I383qv9wl1oOjZIBF5r3/CkwGNRZHu QDKA== X-Gm-Message-State: ANhLgQ3kIJX5mOIuFDzPkLvBSGWeAmfDvjmuvCiiMOAe8DDrxrDp8Orf aFMssdHbhspIKpxaEMo/MNA= X-Google-Smtp-Source: ADFU+vtNTC3uveKLjYkpabv7PlfTxhvxoLbq54nGLzKKlGbyrjTz5Ve6WDJ3HQqFstd4mXXf9AA0aw== X-Received: by 2002:a5d:5687:: with SMTP id f7mr7895856wrv.425.1585215625893; Thu, 26 Mar 2020 02:40:25 -0700 (PDT) Received: from localhost (ip-37-188-135-150.eurotel.cz. [37.188.135.150]) by smtp.gmail.com with ESMTPSA id s22sm2517118wmc.16.2020.03.26.02.40.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2020 02:40:24 -0700 (PDT) Date: Thu, 26 Mar 2020 10:40:23 +0100 From: Michal Hocko 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, Baoquan He , Sachin Sant Subject: Re: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check Message-ID: <20200326094023.GG27965@dhcp22.suse.cz> 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> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 25-03-20 08:49:14, 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 It would be great to match this to the specific source code. > __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. I am sorry, I haven't noticed that during the review of the commit mentioned above. This is all subtle as hell, I have to say. Why do we have to free usage before deactivaing section memmap? Now that we have a late section_mem_map reset shouldn't we tear down the usage in the same branch? > 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 > --- > 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; Btw. this comment is not really helping at all. /* * section->usage is gone and VMEMMAP's pfn_valid depens * on it (see pfn_section_valid) */ > } > > if (section_is_early && memmap) > -- > 2.25.1 > -- Michal Hocko SUSE Labs