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    Subject[PATCH] hugetlb: clarify hugetlb_instantiation_mutex usage
    And the follow up documentation patch:
    ---
    From 51bef05e4cbf97a749e6c0245114eceb21d05d61 Mon Sep 17 00:00:00 2001
    From: Michal Hocko <mhocko@suse.cz>
    Date: Mon, 21 Nov 2011 15:39:45 +0100
    Subject: [PATCH] hugetlb: clarify hugetlb_instantiation_mutex usage

    Let's make it clear that we cannot race with other fault handlers due to
    hugetlb (global) mutex.
    Also make it clear that we want to keep pte_same checks anayway to have a
    transition from the global mutex easier.

    Signed-off-by: Michal Hocko <mhocko@suse.cz>
    ---
    mm/hugetlb.c | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    index f76c7ea..611cdc8 100644
    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -2348,6 +2348,9 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,

    /*
    * Hugetlb_cow() should be called with page lock of the original hugepage held.
    + * Called with hugetlb_instantiation_mutex held and pte_page locked so we
    + * cannot race with other handlers or page migration.
    + * Keep the pte_same checks anyway to make transition from the mutex easier.
    */
    static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
    unsigned long address, pte_t *ptep, pte_t pte,
    --
    1.7.7.1

    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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