From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id CE8AF6B0005 for ; Thu, 12 May 2016 07:37:08 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id s63so61030515wme.2 for ; Thu, 12 May 2016 04:37:08 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id f8si15717559wjy.191.2016.05.12.04.37.07 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 12 May 2016 04:37:07 -0700 (PDT) Subject: Re: [PATCH] mm: fix pfn spans two sections in has_unmovable_pages() References: <57304B9A.40504@huawei.com> <57305AD8.9090202@suse.cz> <57306038.1070907@huawei.com> From: Vlastimil Babka Message-ID: <57346ADA.6050102@suse.cz> Date: Thu, 12 May 2016 13:36:58 +0200 MIME-Version: 1.0 In-Reply-To: <57306038.1070907@huawei.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Xishi Qiu Cc: Andrew Morton , Mel Gorman , Michal Hocko , David Rientjes , "'Kirill A . Shutemov'" , Joonsoo Kim , Taku Izumi , Alexander Duyck , Johannes Weiner , Linux MM , LKML On 05/09/2016 12:02 PM, Xishi Qiu wrote: > On 2016/5/9 17:39, Vlastimil Babka wrote: > >> On 05/09/2016 10:34 AM, Xishi Qiu wrote: >>> If the pfn is not aligned to pageblock, the check pfn may access a next >>> pageblcok, and the next pageblock may belong to a next section. Because >>> struct page has not been alloced in the next section, so kernel panic. >>> >>> I find the caller of has_unmovable_pages() has passed a aligned pfn, so it >>> doesn't have this problem. But the earlier kernel version(e.g. v3.10) has. >>> e.g. echo xxx > /sys/devices/system/memory/soft_offline_page could trigger >>> it. The following log is from RHEL v7.1 >> >> I think has_unmovable_pages() is wrong layer where to fix such problem, as I'll explain below. >> >>> [14111.611492] Stack: >>> [14111.611494] ffffffff8115d952 0000000000000000 01ff880c393ebe40 ffff880c7ffd9000 >>> [14111.611500] ffffea0061ffffc0 ffff880c7ffd9068 0000000000000286 0000000000000001 >>> [14111.611505] ffff880c393ebe10 ffffffff811c265a 000000000187ffff 0000000000000200 >>> [14111.611511] Call Trace: >>> [14111.611516] [] ? has_unmovable_pages+0xd2/0x130 >>> [14111.611521] [] set_migratetype_isolate+0xda/0x170 >>> [14111.611526] [] soft_offline_page+0x9a/0x590 >>> [14111.611530] [] ? _kstrtoull+0x3b/0xa0 >>> [14111.611535] [] store_soft_offline_page+0xaf/0xf0 >>> [14111.611539] [] dev_attr_store+0x18/0x30 >>> [14111.611544] [] sysfs_write_file+0xc6/0x140 >>> [14111.611548] [] vfs_write+0xbd/0x1e0 >>> [14111.611551] [] SyS_write+0x58/0xb0 >>> [14111.611556] [] system_call_fastpath+0x16/0x1b >>> [14111.611559] Code: 66 66 66 90 48 83 e0 fd 0c a0 5d c3 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 66 66 66 90 48 83 c8 42 0c a0 5d c3 90 66 66 66 66 90 <8b> 07 25 00 c0 00 00 75 02 f3 c3 48 8b 07 f6 c4 80 75 0f 48 81 >>> [14111.611594] RIP [] PageHuge+0x5/0x40 >>> [14111.611598] RSP >>> [14111.611600] CR2: ffffea0062000000 >>> [14111.611604] ---[ end trace 9f780ed1def334c6 ]--- >>> [14111.678586] Kernel panic - not syncing: Fatal exception >>> >>> Signed-off-by: Xishi Qiu >> >> It's not CC'd stable, so how will this patch fix the older kernels? Also you should determine which upstream kernel versions are affected, not a RHEL derivative. >> Also is the current upstream broken or not? >> > > OK, I'll resend it later. The current upstream has not this problem. > >>> --- >>> mm/page_alloc.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 59de90d..9afc1bc 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -6842,6 +6842,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, >>> return false; >>> >>> pfn = page_to_pfn(page); >>> + pfn = pfn & ~(pageblock_nr_pages - 1); >> >> I think it's wrong that has_unmovable_pages() would silently correct wrong input. See e.g. the call path from start_isolate_page_range -> set_migratetype_isolate -> has_unmovable_pages. In start_isolate_page_range() there are BUG_ON's to check the alignment. That would be more appropriate here as well (but use VM_BUG_ON please). >> > > Yes, this path is correct. > > But the older kernel like the following path has the problem. > soft_offline_page > get_any_page > __get_any_page > set_migratetype_isolate > has_unmovable_pages > >> One danger of the self-correction is that the adjusted pfn might be of >> a different zone, so let's not go there. If there's a call stack that passes unaligned page, it has to be fixed higher in the stack IMHO. >> > > How about change the pfn when calling set_migratetype_isolate()? > e.g. set_migratetype_isolate((p & ~(pageblock_nr_pages - 1)), true); Sounds ok, please try. > > Thanks, > Xishi Qiu > >>> for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) { >>> unsigned long check = pfn + iter; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org