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    Subject[PATCHv4 18/24] thp, mm: split_huge_page(): caller need to lock page
    Date
    We're going to use migration entries instead of compound_lock() to
    stabilize page refcounts. Setup and remove migration entries require
    page to be locked.

    Some of split_huge_page() callers already have the page locked. Let's
    require everybody to lock the page before calling split_huge_page().

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    mm/huge_memory.c | 1 +
    mm/ksm.c | 6 ++++--
    mm/memory-failure.c | 12 +++++++++---
    mm/migrate.c | 8 ++++++--
    4 files changed, 20 insertions(+), 7 deletions(-)

    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index 3741f81e423e..f1d88b9059e2 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -1846,6 +1846,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)

    BUG_ON(is_huge_zero_page(page));
    BUG_ON(!PageAnon(page));
    + BUG_ON(!PageLocked(page));

    /*
    * The caller does not necessarily hold an mmap_sem that would prevent
    diff --git a/mm/ksm.c b/mm/ksm.c
    index 92182eeba87d..a8a88b0f6f62 100644
    --- a/mm/ksm.c
    +++ b/mm/ksm.c
    @@ -987,9 +987,11 @@ static int page_trans_compound_anon_split(struct page *page)
    * Recheck we got the reference while the head
    * was still anonymous.
    */
    - if (PageAnon(transhuge_head))
    + if (PageAnon(transhuge_head)) {
    + lock_page(transhuge_head);
    ret = split_huge_page(transhuge_head);
    - else
    + unlock_page(transhuge_head);
    + } else
    /*
    * Retry later if split_huge_page run
    * from under us.
    diff --git a/mm/memory-failure.c b/mm/memory-failure.c
    index d487f8dc6d39..74c5aaddae85 100644
    --- a/mm/memory-failure.c
    +++ b/mm/memory-failure.c
    @@ -950,7 +950,10 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
    * enough * to be safe.
    */
    if (!PageHuge(hpage) && PageAnon(hpage)) {
    - if (unlikely(split_huge_page(hpage))) {
    + lock_page(hpage);
    + ret = split_huge_page(hpage);
    + unlock_page(hpage);
    + if (unlikely(ret)) {
    /*
    * FIXME: if splitting THP is failed, it is
    * better to stop the following operation rather
    @@ -1694,10 +1697,13 @@ int soft_offline_page(struct page *page, int flags)
    return -EBUSY;
    }
    if (!PageHuge(page) && PageTransHuge(hpage)) {
    - if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
    + lock_page(page);
    + ret = split_huge_page(hpage);
    + unlock_page(page);
    + if (unlikely(ret)) {
    pr_info("soft offline: %#lx: failed to split THP\n",
    pfn);
    - return -EBUSY;
    + return ret;
    }
    }

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 01449826b914..91a67029bb18 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -920,9 +920,13 @@ static int unmap_and_move(new_page_t get_new_page, free_page_t put_new_page,
    goto out;
    }

    - if (unlikely(PageTransHuge(page)))
    - if (unlikely(split_huge_page(page)))
    + if (unlikely(PageTransHuge(page))) {
    + lock_page(page);
    + rc = split_huge_page(page);
    + unlock_page(page);
    + if (rc)
    goto out;
    + }

    rc = __unmap_and_move(page, newpage, force, mode);

    --
    2.1.4


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