Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752891Ab2JBMYT (ORCPT ); Tue, 2 Oct 2012 08:24:19 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:59899 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752218Ab2JBMYQ (ORCPT ); Tue, 2 Oct 2012 08:24:16 -0400 Message-ID: <506ADCE0.1020602@gmail.com> Date: Tue, 02 Oct 2012 20:24:00 +0800 From: Ni zhan Chen User-Agent: Mozilla/5.0 (X11; Linux i686; rv:15.0) Gecko/20120912 Thunderbird/15.0.1 MIME-Version: 1.0 To: Yasuaki Ishimatsu CC: x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-acpi@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-ia64@vger.kernel.org, cmetcalf@tilera.com, sparclinux@vger.kernel.org, rientjes@google.com, liuj97@gmail.com, len.brown@intel.com, benh@kernel.crashing.org, paulus@samba.org, cl@linux.com, minchan.kim@gmail.com, akpm@linux-foundation.org, kosaki.motohiro@jp.fujitsu.com, Wen Congyang Subject: Re: [RFC v9 PATCH 13/21] memory-hotplug: check page type in get_page_bootmem References: <1346837155-534-1-git-send-email-wency@cn.fujitsu.com> <1346837155-534-14-git-send-email-wency@cn.fujitsu.com> <506659D7.9080904@gmail.com> <506907E5.2080609@jp.fujitsu.com> In-Reply-To: <506907E5.2080609@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3937 Lines: 103 On 10/01/2012 11:03 AM, Yasuaki Ishimatsu wrote: > Hi Chen, > > 2012/09/29 11:15, Ni zhan Chen wrote: >> On 09/05/2012 05:25 PM, wency@cn.fujitsu.com wrote: >>> From: Yasuaki Ishimatsu >>> >>> The function get_page_bootmem() may be called more than one time to >>> the same >>> page. There is no need to set page's type, private if the function >>> is not >>> the first time called to the page. >>> >>> Note: the patch is just optimization and does not fix any problem. >> >> Hi Yasuaki, >> >> this patch is reasonable to me. I have another question associated to >> get_page_bootmem(), the question is from another fujitsu guy's patch >> changelog [commit : 04753278769f3], the changelog said that: >> >> 1) When the memmap of removing section is allocated on other >> section by bootmem, it should/can be free. >> 2) When the memmap of removing section is allocated on the >> same section, it shouldn't be freed. Because the section has to be >> logical memory offlined already and all pages must be isolated >> against >> page allocater. If it is freed, page allocator may use it which >> will >> be removed physically soon. >> >> but I don't see his patch guarantee 2), it means that his patch >> doesn't guarantee the memmap of removing section which is allocated >> on other section by bootmem doesn't be freed. Hopefully get your >> explaination in details, thanks in advance. :-) > > In my understanding, the patch does not guarantee it. > Please see [commit : 0c0a4a517a31e]. free_map_bootmem() in the commit > guarantees it. Thanks Yasuaki, I have already seen the commit you mentioned. But the changelog of the commit I point out 2), why it said that "If it is freed, page allocator may use it which will be removed physically soon", does it mean that use-after-free ? AFAK, the isolated pages will be free if no users use it, so why not free the associated memmap? > > Thanks, > Yasuaki Ishimatsu > >> >>> >>> CC: David Rientjes >>> CC: Jiang Liu >>> CC: Len Brown >>> CC: Benjamin Herrenschmidt >>> CC: Paul Mackerras >>> CC: Christoph Lameter >>> Cc: Minchan Kim >>> CC: Andrew Morton >>> CC: KOSAKI Motohiro >>> CC: Wen Congyang >>> Signed-off-by: Yasuaki Ishimatsu >>> --- >>> mm/memory_hotplug.c | 15 +++++++++++---- >>> 1 files changed, 11 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index d736df3..26a5012 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -95,10 +95,17 @@ static void release_memory_resource(struct >>> resource *res) >>> static void get_page_bootmem(unsigned long info, struct page *page, >>> unsigned long type) >>> { >>> - page->lru.next = (struct list_head *) type; >>> - SetPagePrivate(page); >>> - set_page_private(page, info); >>> - atomic_inc(&page->_count); >>> + unsigned long page_type; >>> + >>> + page_type = (unsigned long)page->lru.next; >>> + if (page_type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE || >>> + page_type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE){ >>> + page->lru.next = (struct list_head *)type; >>> + SetPagePrivate(page); >>> + set_page_private(page, info); >>> + atomic_inc(&page->_count); >>> + } else >>> + atomic_inc(&page->_count); >>> } >>> /* reference to __meminit __free_pages_bootmem is valid >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/