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    Subject[RFC PATCH v2 02/16] mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED
    Date
    From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

    The call to get_user_pages_fast is only to get the pointer to a struct
    page of a given address, pinning it is memory-poisoning handler's job,
    so drop the refcount grabbed by get_user_pages_fast

    Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Signed-off-by: Oscar Salvador <osalvador@suse.de>
    ---
    mm/madvise.c | 24 ++++++++++++------------
    1 file changed, 12 insertions(+), 12 deletions(-)

    diff --git a/mm/madvise.c b/mm/madvise.c
    index 2be9f3fdb05e..89ed9a22ff4f 100644
    --- a/mm/madvise.c
    +++ b/mm/madvise.c
    @@ -878,16 +878,24 @@ static int madvise_inject_error(int behavior,
    */
    order = compound_order(compound_head(page));

    - if (PageHWPoison(page)) {
    - put_page(page);
    + /*
    + * The get_user_pages_fast() is just to get the pfn of the
    + * given address, and the refcount has nothing to do with
    + * what we try to test, so it should be released immediately.
    + * This is racy but it's intended because the real hardware
    + * errors could happen at any moment and memory error handlers
    + * must properly handle the race.
    + */
    + put_page(page);
    +
    + if (PageHWPoison(page))
    continue;
    - }

    if (behavior == MADV_SOFT_OFFLINE) {
    pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
    pfn, start);

    - ret = soft_offline_page(page, MF_COUNT_INCREASED);
    + ret = soft_offline_page(page, 0);
    if (ret)
    return ret;
    continue;
    @@ -895,14 +903,6 @@ static int madvise_inject_error(int behavior,

    pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
    pfn, start);
    -
    - /*
    - * Drop the page reference taken by get_user_pages_fast(). In
    - * the absence of MF_COUNT_INCREASED the memory_failure()
    - * routine is responsible for pinning the page to prevent it
    - * from being released back to the page allocator.
    - */
    - put_page(page);
    ret = memory_failure(pfn, 0);
    if (ret)
    return ret;
    --
    2.12.3
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