From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) by kanga.kvack.org (Postfix) with ESMTP id A9DFA6B000D for ; Mon, 5 Nov 2018 10:06:34 -0500 (EST) Received: by mail-pg1-f197.google.com with SMTP id 18-v6so8699954pgn.4 for ; Mon, 05 Nov 2018 07:06:34 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com. [148.163.156.1]) by mx.google.com with ESMTPS id e129-v6si9184815pfg.205.2018.11.05.07.06.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Nov 2018 07:06:33 -0800 (PST) Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wA5F64iO002181 for ; Mon, 5 Nov 2018 10:06:32 -0500 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0a-001b2d01.pphosted.com with ESMTP id 2njpy841cf-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 05 Nov 2018 10:06:27 -0500 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 5 Nov 2018 15:04:06 -0000 From: Mikhail Zaslonko Subject: [PATCH v2 0/1] memory_hotplug: fix the panic when memory end is not Date: Mon, 5 Nov 2018 16:04:00 +0100 Message-Id: <20181105150401.97287-1-zaslonko@linux.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, Pavel.Tatashin@microsoft.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, gerald.schaefer@de.ibm.com, zaslonko@linux.ibm.com This patch refers to the older thread: https://marc.info/?t=153658306400001&r=1&w=2 I have tried to take the approaches suggested in the discussion like simply ignoring unaligned memory to section memory much earlier or initializing struct pages beyond the "end" but both had issues. First I tried to ignore unaligned memory early by adjusting memory_end value. But the thing is that kernel mem parameter parsing and memory_end calculation take place in the architecture code and adjusting it afterwards in common code might be too late in my view. Also with this approach we might lose the memory up to the entire section(256Mb on s390) just because of unfortunate alignment. Another approach was to fix memmap_init() and initialize struct pages beyond the end. Since struct pages are allocated section-wise we can try to round the size parameter passed to the memmap_init() function up to the section boundary thus forcing the mapping initialization for the entire section. But then it leads to another VM_BUG_ON panic due to zone_spans_pfn() sanity check triggered for the first page of each page block from set_pageblock_migratetype() function: page dumped because: VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn)) Call Trace: ([<00000000003013f8>] set_pfnblock_flags_mask+0xe8/0x140) [<00000000003014aa>] set_pageblock_migratetype+0x5a/0x70 [<0000000000bef706>] memmap_init_zone+0x25e/0x2e0 [<00000000010fc3d8>] free_area_init_node+0x530/0x558 [<00000000010fcf02>] free_area_init_nodes+0x81a/0x8f0 [<00000000010e7fdc>] paging_init+0x124/0x130 [<00000000010e4dfa>] setup_arch+0xbf2/0xcc8 [<00000000010de9e6>] start_kernel+0x7e/0x588 [<000000000010007c>] startup_continue+0x7c/0x300 Last Breaking-Event-Address: [<00000000003013f8>] set_pfnblock_flags_mask+0xe8/0x1401 We might ignore this check for the struct pages beyond the "end" but I'm not sure about further implications. For now I suggest to stay with my original proposal fixing specific functions for memory hotplug sysfs handlers. Changes v1 -> v2: * Expanded commit message to show both failing scenarious. * Use 'pfn + i' instead of 'pfn' for zone_spans_pfn() check within test_pages_in_a_zone() function thus taking CONFIG_HOLES_IN_ZONE into consideration. Mikhail Zaslonko (1): memory_hotplug: fix the panic when memory end is not on the section boundary mm/memory_hotplug.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) -- 2.16.4