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    Subject[PATCH 3.12 062/104] mm: hugetlb: fix copy_hugetlb_page_range()
    Date
    From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit 0253d634e0803a8376a0d88efee0bf523d8673f9 upstream.

    Commit 4a705fef9862 ("hugetlb: fix copy_hugetlb_page_range() to handle
    migration/hwpoisoned entry") changed the order of
    huge_ptep_set_wrprotect() and huge_ptep_get(), which leads to breakage
    in some workloads like hugepage-backed heap allocation via libhugetlbfs.
    This patch fixes it.

    The test program for the problem is shown below:

    $ cat heap.c
    #include <unistd.h>
    #include <stdlib.h>
    #include <string.h>

    #define HPS 0x200000

    int main() {
    int i;
    char *p = malloc(HPS);
    memset(p, '1', HPS);
    for (i = 0; i < 5; i++) {
    if (!fork()) {
    memset(p, '2', HPS);
    p = malloc(HPS);
    memset(p, '3', HPS);
    free(p);
    return 0;
    }
    }
    sleep(1);
    free(p);
    return 0;
    }

    $ export HUGETLB_MORECORE=yes ; export HUGETLB_NO_PREFAULT= ; hugectl --heap ./heap

    Fixes 4a705fef9862 ("hugetlb: fix copy_hugetlb_page_range() to handle
    migration/hwpoisoned entry"), so is applicable to -stable kernels which
    include it.

    Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Reported-by: Guillaume Morin <guillaume@morinfr.org>
    Suggested-by: Guillaume Morin <guillaume@morinfr.org>
    Acked-by: Hugh Dickins <hughd@google.com>
    Cc: <stable@vger.kernel.org> [2.6.37+]
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    mm/hugetlb.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    index 11c2b7fed052..f80b17106d24 100644
    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -2453,6 +2453,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
    } else {
    if (cow)
    huge_ptep_set_wrprotect(src, addr, src_pte);
    + entry = huge_ptep_get(src_pte);
    ptepage = pte_page(entry);
    get_page(ptepage);
    page_dup_rmap(ptepage);
    --
    2.0.4


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