From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 759DE8E0018 for ; Mon, 10 Dec 2018 10:45:42 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id f17so4356037edm.20 for ; Mon, 10 Dec 2018 07:45:42 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id g51si2879012edg.7.2018.12.10.07.45.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Dec 2018 07:45:40 -0800 (PST) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wBAFiuMF188664 for ; Mon, 10 Dec 2018 10:45:39 -0500 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0b-001b2d01.pphosted.com with ESMTP id 2p9rxk6ysf-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 10 Dec 2018 10:45:38 -0500 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 10 Dec 2018 15:45:37 -0000 Subject: Re: [PATCH 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section References: <20181210130712.30148-1-zaslonko@linux.ibm.com> <20181210130712.30148-2-zaslonko@linux.ibm.com> <20181210132451.GO1286@dhcp22.suse.cz> From: Zaslonko Mikhail Date: Mon, 10 Dec 2018 16:45:37 +0100 MIME-Version: 1.0 In-Reply-To: <20181210132451.GO1286@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Mikhail Zaslonko Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Pavel.Tatashin@microsoft.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, gerald.schaefer@de.ibm.com Hello, On 10.12.2018 14:24, Michal Hocko wrote: > On Mon 10-12-18 14:07:12, 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. > > It would be great to mention how you can end up in the situation like > this(a user provided memmap or a strange HW). Yes, I should probably keep full failure samples from my previous patch version. > >> 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: >> >> 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 >> >> Fix the problem by initializing the last memory section of the highest zone >> in memmap_init_zone() till the very end, even if it goes beyond the zone >> end. > > Why do we need to restrict this to the highest zone? In other words, why > cannot we do what I was suggesting earlier [1]. What does prevent other > zones to have an incomplete section boundary? Well, as you were also suggesting earlier: 'If we do not have a zone which spans the rest of the section'. I'm not sure how else we should verify that. Moreover, I was able to recreate the problem only with the highest zone (memory end is not on the section boundary). > > [1] http://lkml.kernel.org/r/20181105183533.GQ4361@dhcp22.suse.cz > >> Signed-off-by: Mikhail Zaslonko >> Reviewed-by: Gerald Schaefer >> Cc: >> --- >> mm/page_alloc.c | 15 +++++++++++++++ >> 1 file changed, 15 insertions(+) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 2ec9cc407216..41ef5508e5f1 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -5542,6 +5542,21 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, >> cond_resched(); >> } >> } >> +#ifdef CONFIG_SPARSEMEM >> + /* >> + * If there is no zone spanning 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). >> + */ >> + if (end_pfn == max_pfn) { >> + while (end_pfn % PAGES_PER_SECTION) { >> + __init_single_page(pfn_to_page(end_pfn), end_pfn, zone, >> + nid); >> + end_pfn++; >> + } >> + } >> +#endif >> } >> >> #ifdef CONFIG_ZONE_DEVICE >> -- >> 2.16.4 > Thanks, Mikhail Zaslonko