From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f197.google.com (mail-qt1-f197.google.com [209.85.160.197]) by kanga.kvack.org (Postfix) with ESMTP id D85C88E01DC for ; Fri, 14 Dec 2018 10:49:18 -0500 (EST) Received: by mail-qt1-f197.google.com with SMTP id n50so5575081qtb.9 for ; Fri, 14 Dec 2018 07:49:18 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id r1si807280qkk.116.2018.12.14.07.49.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Dec 2018 07:49:18 -0800 (PST) Subject: Re: [PATCH v2 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section From: David Hildenbrand References: <20181212172712.34019-1-zaslonko@linux.ibm.com> <20181212172712.34019-2-zaslonko@linux.ibm.com> <476a80cb-5524-16c1-6dd5-da5febbd6139@redhat.com> Message-ID: Date: Fri, 14 Dec 2018 16:49:14 +0100 MIME-Version: 1.0 In-Reply-To: <476a80cb-5524-16c1-6dd5-da5febbd6139@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mikhail Zaslonko , 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 On 14.12.18 16:22, David Hildenbrand wrote: > On 12.12.18 18:27, Mikhail Zaslonko wrote: >> If memory end is not aligned with the sparse memory section boundary, the >> mapping of such a section is only partly initialized. This may lead to >> VM_BUG_ON due to uninitialized struct page access from >> is_mem_section_removable() or test_pages_in_a_zone() function triggered by >> memory_hotplug sysfs handlers: >> >> Here are the the panic examples: >> CONFIG_DEBUG_VM=y >> CONFIG_DEBUG_VM_PGFLAGS=y >> >> kernel parameter mem=2050M >> -------------------------- >> page:000003d082008000 is uninitialized and poisoned >> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) >> Call Trace: >> ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160) >> [<00000000008f15c4>] show_valid_zones+0x5c/0x190 >> [<00000000008cf9c4>] dev_attr_show+0x34/0x70 >> [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 >> [<00000000003e4194>] seq_read+0x204/0x480 >> [<00000000003b53ea>] __vfs_read+0x32/0x178 >> [<00000000003b55b2>] vfs_read+0x82/0x138 >> [<00000000003b5be2>] ksys_read+0x5a/0xb0 >> [<0000000000b86ba0>] system_call+0xdc/0x2d8 >> Last Breaking-Event-Address: >> [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160 >> Kernel panic - not syncing: Fatal exception: panic_on_oops >> >> kernel parameter mem=3075M >> -------------------------- >> page:000003d08300c000 is uninitialized and poisoned >> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) >> Call Trace: >> ([<000000000038596c>] is_mem_section_removable+0xb4/0x190) >> [<00000000008f12fa>] show_mem_removable+0x9a/0xd8 >> [<00000000008cf9c4>] dev_attr_show+0x34/0x70 >> [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 >> [<00000000003e4194>] seq_read+0x204/0x480 >> [<00000000003b53ea>] __vfs_read+0x32/0x178 >> [<00000000003b55b2>] vfs_read+0x82/0x138 >> [<00000000003b5be2>] ksys_read+0x5a/0xb0 >> [<0000000000b86ba0>] system_call+0xdc/0x2d8 >> Last Breaking-Event-Address: >> [<000000000038596c>] is_mem_section_removable+0xb4/0x190 >> Kernel panic - not syncing: Fatal exception: panic_on_oops >> >> Fix the problem by initializing the last memory section of each zone >> in memmap_init_zone() till the very end, even if it goes beyond the zone >> end. >> >> Signed-off-by: Mikhail Zaslonko >> Reviewed-by: Gerald Schaefer >> Cc: >> --- >> mm/page_alloc.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 2ec9cc407216..e2afdb2dc2c5 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -5542,6 +5542,18 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, >> cond_resched(); >> } >> } >> +#ifdef CONFIG_SPARSEMEM >> + /* >> + * If the zone does not span the rest of the section then >> + * we should at least initialize those pages. Otherwise we >> + * could blow up on a poisoned page in some paths which depend >> + * on full sections being initialized (e.g. memory hotplug). >> + */ >> + while (end_pfn % PAGES_PER_SECTION) { >> + __init_single_page(pfn_to_page(end_pfn), end_pfn, zone, nid); >> + end_pfn++; > > This page will not be marked as PG_reserved - although it is a physical > memory gap. Do we care? > Hm, or do we even have any idea what this is (e.g. could it also be something not a gap)? For physical memory gaps within a section, architectures usually exclude that memory from getting passed to e.g. the page allocator by memblock_reserve(). Before handing all free pages to the page allocator, all such reserved memblocks will be marked reserved. But this here seems to be different. We don't have a previous memblock_reserve(), because otherwise these pages would have properly been initialized already when marking them reserved. -- Thanks, David / dhildenb