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    Subject[023/127] mm: fix is_mem_section_removable() page_order BUG_ON check
    2.6.32-stable review patch.  If anyone has any objections, please let us know.


    From: KAMEZAWA Hiroyuki <>

    commit 572438f9b52236bd8938b1647cc15e027d27ef55 upstream.

    page_order() is called by memory hotplug's user interface to check the
    section is removable or not. (is_mem_section_removable())

    It calls page_order() withoug holding zone->lock.
    So, even if the caller does

    if (PageBuddy(page))
    ret = page_order(page) ...
    The caller may hit BUG_ON().

    For fixing this, there are 2 choices.
    1. add zone->lock.
    2. remove BUG_ON().

    is_mem_section_removable() is used for some "advice" and doesn't need to
    be 100% accurate. This is_removable() can be called via user program..
    We don't want to take this important lock for long by user's request. So,
    this patch removes BUG_ON().

    Signed-off-by: KAMEZAWA Hiroyuki <>
    Acked-by: Wu Fengguang <>
    Acked-by: Michal Hocko <>
    Acked-by: Mel Gorman <>
    Signed-off-by: Andrew Morton <>
    Signed-off-by: Linus Torvalds <>
    Signed-off-by: Greg Kroah-Hartman <>

    mm/internal.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/mm/internal.h
    +++ b/mm/internal.h
    @@ -59,7 +59,7 @@ extern void prep_compound_page(struct pa
    static inline unsigned long page_order(struct page *page)
    - VM_BUG_ON(!PageBuddy(page));
    + /* PageBuddy() must be checked by the caller */
    return page_private(page);

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      Last update: 2010-12-08 01:49    [W:0.020 / U:18.688 seconds]
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