Messages in this thread | | | Date | Tue, 02 Oct 2012 20:24:00 +0800 | From | Ni zhan Chen <> | Subject | Re: [RFC v9 PATCH 13/21] memory-hotplug: check page type in get_page_bootmem |
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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 <isimatu.yasuaki@jp.fujitsu.com> >>> >>> 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 <rientjes@google.com> >>> CC: Jiang Liu <liuj97@gmail.com> >>> CC: Len Brown <len.brown@intel.com> >>> CC: Benjamin Herrenschmidt <benh@kernel.crashing.org> >>> CC: Paul Mackerras <paulus@samba.org> >>> CC: Christoph Lameter <cl@linux.com> >>> Cc: Minchan Kim <minchan.kim@gmail.com> >>> CC: Andrew Morton <akpm@linux-foundation.org> >>> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> >>> CC: Wen Congyang <wency@cn.fujitsu.com> >>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> >>> --- >>> 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 >> > > >
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