On 10/01/2012 11:03 AM, Yasuaki Ishimatsu wrote:

Hi Chen,

2012/09/29 11:15, Ni zhan Chen wrote:

quoted

On 09/05/2012 05:25 PM, wency@cn.fujitsu.com wrote:

quoted

From: Yasuaki Ishimatsu <redacted>

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

quoted

quoted

CC: David Rientjes <rientjes@google.com>
CC: Jiang Liu <redacted>
CC: Len Brown <redacted>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <redacted>
CC: Christoph Lameter <redacted>
Cc: Minchan Kim <redacted>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: KOSAKI Motohiro <redacted>
CC: Wen Congyang <redacted>
Signed-off-by: Yasuaki Ishimatsu <redacted>
---
  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