From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f176.google.com (mail-pd0-f176.google.com [209.85.192.176]) by kanga.kvack.org (Postfix) with ESMTP id 50C2C6B0038 for ; Tue, 9 Dec 2014 20:41:19 -0500 (EST) Received: by mail-pd0-f176.google.com with SMTP id y10so1717663pdj.7 for ; Tue, 09 Dec 2014 17:41:19 -0800 (PST) Received: from fgwmail5.fujitsu.co.jp (fgwmail5.fujitsu.co.jp. [192.51.44.35]) by mx.google.com with ESMTPS id nt1si4267919pbc.196.2014.12.09.17.41.16 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 09 Dec 2014 17:41:17 -0800 (PST) Received: from kw-mxoi2.gw.nic.fujitsu.com (unknown [10.0.237.143]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id 2E4313EE1AB for ; Wed, 10 Dec 2014 10:41:15 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by kw-mxoi2.gw.nic.fujitsu.com (Postfix) with ESMTP id 42B2DAC046B for ; Wed, 10 Dec 2014 10:41:14 +0900 (JST) Received: from g01jpfmpwkw01.exch.g01.fujitsu.local (g01jpfmpwkw01.exch.g01.fujitsu.local [10.0.193.38]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id E3508E08002 for ; Wed, 10 Dec 2014 10:41:13 +0900 (JST) Message-ID: <5487A418.4060800@jp.fujitsu.com> Date: Wed, 10 Dec 2014 10:38:32 +0900 From: Yasuaki Ishimatsu MIME-Version: 1.0 Subject: Re: [PATCH] mm: fix invalid use of pfn_valid_within in test_pages_in_a_zone References: <1418153696-167580-1-git-send-email-jcuster@sgi.com>,<54878D56.4030508@jp.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: James Custer , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "kamezawa.hiroyu@jp.fujitsu.com" Cc: Russ Anderson , Derek Fults (2014/12/10 9:14), James Custer wrote: > It is exactly the same if CONFIG_HOLES_IN_NODE is set, but if CONFIG_HOLES_IN_NODE is not set, then pfn_valid_within is always 1. Why don't you set CONFIG_HOLES_IN_ZONE? This BUG is occrred by hole in zone. CONFIG_HOLE_IN_ZONE is propered for the system. I think your patch fixes the BUG. But even if fixing the BUG, other issues will be occurred by hole in zone. Thanks, Yasuaki Ishimatsu > > From: https://lkml.org/lkml/2007/3/21/272 > > "Generally we work under the assumption that memory the mem_map > array is contigious and valid out to MAX_ORDER_NR_PAGES block > of pages, ie. that if we have validated any page within this > MAX_ORDER_NR_PAGES block we need not check any other. This is not > true when CONFIG_HOLES_IN_ZONE is set and we must check each and > every reference we make from a pfn. > > Add a pfn_valid_within() helper which should be used when scanning > pages within a MAX_ORDER_NR_PAGES block when we have already > checked the validility of the block normally with pfn_valid(). > This can then be optimised away when we do not have holes within > a MAX_ORDER_NR_PAGES block of pages." > > So, since we're iterating over a pageblock there must be a valid pfn to be able to use pfn_valid_within (which makes sense since if CONFIG_HOLES_IN_NODE is not set, it is always 1). > > I'm just going off of the documentation there and what makes sense to me based off that documentation. Does that explanation help? > > Regards, > James Custer > ________________________________________ > From: Yasuaki Ishimatsu [isimatu.yasuaki@jp.fujitsu.com] > Sent: Tuesday, December 09, 2014 6:01 PM > To: James Custer; linux-kernel@vger.kernel.org; linux-mm@kvack.org; akpm@linux-foundation.org; kamezawa.hiroyu@jp.fujitsu.com > Cc: Russ Anderson; Derek Fults > Subject: Re: [PATCH] mm: fix invalid use of pfn_valid_within in test_pages_in_a_zone > > (2014/12/10 4:34), James Custer wrote: >> Offlining memory by 'echo 0 > /sys/devices/system/memory/memory#/online' >> or reading valid_zones 'cat /sys/devices/system/memory/memory#/valid_zones' > >> causes BUG: unable to handle kernel paging request due to invalid use of >> pfn_valid_within. This is due to a bug in test_pages_in_a_zone. > > The information is not enough to understand what happened on your system. > Could you show full BUG messages? > >> >> In order to use pfn_valid_within within a MAX_ORDER_NR_PAGES block of pages, >> a valid pfn within the block must first be found. There only needs to be >> one valid pfn found in test_pages_in_a_zone in the first place. So the >> fix is to replace pfn_valid_within with pfn_valid such that the first >> valid pfn within the pageblock is found (if it exists). This works >> independently of CONFIG_HOLES_IN_ZONE. >> >> Signed-off-by: James Custer >> --- >> mm/memory_hotplug.c | 11 ++++++----- >> 1 file changed, 6 insertions(+), 5 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 1bf4807..304c187 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1331,7 +1331,7 @@ int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) >> } >> >> /* >> - * Confirm all pages in a range [start, end) is belongs to the same zone. >> + * Confirm all pages in a range [start, end) belong to the same zone. >> */ >> int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn) >> { >> @@ -1342,10 +1342,11 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn) >> for (pfn = start_pfn; >> pfn < end_pfn; >> pfn += MAX_ORDER_NR_PAGES) { > >> - i = 0; >> - /* This is just a CONFIG_HOLES_IN_ZONE check.*/ >> - while ((i < MAX_ORDER_NR_PAGES) && !pfn_valid_within(pfn + i)) >> - i++; >> + /* Find the first valid pfn in this pageblock */ >> + for (i = 0; i < MAX_ORDER_NR_PAGES; i++) { >> + if (pfn_valid(pfn + i)) >> + break; >> + } > > If CONFIG_HOLES_IN_NODE is set, there is no difference. Am I making a mistake? > > Thanks, > Yasuaki Ishimatsu > > >> if (i == MAX_ORDER_NR_PAGES) >> continue; >> page = pfn_to_page(pfn + i); >> > > -- 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