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Tue, 03 Mar 2020 03:34:59 -0500 X-MC-Unique: o3BWzDYJPTeemXvsxruLzg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1E3DD107B272; Tue, 3 Mar 2020 08:34:58 +0000 (UTC) Received: from [10.36.117.113] (ovpn-117-113.ams2.redhat.com [10.36.117.113]) by smtp.corp.redhat.com (Postfix) with ESMTP id EF8E973868; Tue, 3 Mar 2020 08:34:55 +0000 (UTC) Subject: Re: [PATCH v2 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case To: Baoquan He , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, osalvador@suse.de, dan.j.williams@intel.com, mhocko@suse.com, rppt@linux.ibm.com, robin.murphy@arm.com References: <20200220043316.19668-1-bhe@redhat.com> <20200220043316.19668-2-bhe@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200220043316.19668-2-bhe@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20.02.20 05:33, Baoquan He wrote: > In section_deactivate(), pfn_to_page() doesn't work any more after > ms->section_mem_map is resetting to NULL in SPARSEMEM|!VMEMMAP case. > It caused hot remove failure: > > kernel BUG at mm/page_alloc.c:4806! > invalid opcode: 0000 [#1] SMP PTI > CPU: 3 PID: 8 Comm: kworker/u16:0 Tainted: G W 5.5.0-next-20200205+ #340 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 > Workqueue: kacpi_hotplug acpi_hotplug_work_fn > RIP: 0010:free_pages+0x85/0xa0 > Call Trace: > __remove_pages+0x99/0xc0 > arch_remove_memory+0x23/0x4d > try_remove_memory+0xc8/0x130 > ? walk_memory_blocks+0x72/0xa0 > __remove_memory+0xa/0x11 > acpi_memory_device_remove+0x72/0x100 > acpi_bus_trim+0x55/0x90 > acpi_device_hotplug+0x2eb/0x3d0 > acpi_hotplug_work_fn+0x1a/0x30 > process_one_work+0x1a7/0x370 > worker_thread+0x30/0x380 > ? flush_rcu_work+0x30/0x30 > kthread+0x112/0x130 > ? kthread_create_on_node+0x60/0x60 > ret_from_fork+0x35/0x40 > > Let's move the ->section_mem_map resetting after depopulate_section_memmap() > to fix it. > > Signed-off-by: Baoquan He > --- > mm/sparse.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/sparse.c b/mm/sparse.c > index 596b2a45b100..b8e52c8fed7f 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -779,13 +779,15 @@ 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); > - ms->section_mem_map = (unsigned long)NULL; > } > > if (section_is_early && memmap) > free_map_bootmem(memmap); > else > depopulate_section_memmap(pfn, nr_pages, altmap); > + > + if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) > + ms->section_mem_map = (unsigned long)NULL; > } > > static struct page * __meminit section_activate(int nid, unsigned long pfn, > As discussed, I think this is broken here already. As you explained, the subsection_map can get freed via kfree(ms->usage) after the first bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION) check. -- Thanks, David / dhildenb