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    Subject[PATCH 3.16 142/346] mm/hugetlb: avoid soft lockup in set_max_huge_pages()
    3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jia He <hejianet@gmail.com>

    commit 649920c6ab93429b94bc7c1aa7c0e8395351be32 upstream.

    In powerpc servers with large memory(32TB), we watched several soft
    lockups for hugepage under stress tests.

    The call traces are as follows:
    1.
    get_page_from_freelist+0x2d8/0xd50
    __alloc_pages_nodemask+0x180/0xc20
    alloc_fresh_huge_page+0xb0/0x190
    set_max_huge_pages+0x164/0x3b0

    2.
    prep_new_huge_page+0x5c/0x100
    alloc_fresh_huge_page+0xc8/0x190
    set_max_huge_pages+0x164/0x3b0

    This patch fixes such soft lockups. It is safe to call cond_resched()
    there because it is out of spin_lock/unlock section.

    Link: http://lkml.kernel.org/r/1469674442-14848-1-git-send-email-hejianet@gmail.com
    Signed-off-by: Jia He <hejianet@gmail.com>
    Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    mm/hugetlb.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -1655,6 +1655,10 @@ static unsigned long set_max_huge_pages(
    * and reducing the surplus.
    */
    spin_unlock(&hugetlb_lock);
    +
    + /* yield cpu to avoid soft lockup */
    + cond_resched();
    +
    if (hstate_is_gigantic(h))
    ret = alloc_fresh_gigantic_page(h, nodes_allowed);
    else
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