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    Subject[PATCH v3 03/15] mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED
    Date
    From: Naoya Horiguchi <naoya.horiguchi@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().

    Note that the target page is still pinned after this put_page() because
    the current process should have refcount from mapping.

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

    diff --git v5.8-rc1-mmots-2020-06-20-21-44/mm/madvise.c v5.8-rc1-mmots-2020-06-20-21-44_patched/mm/madvise.c
    index dd1d43cf026d..275b08edd428 100644
    --- v5.8-rc1-mmots-2020-06-20-21-44/mm/madvise.c
    +++ v5.8-rc1-mmots-2020-06-20-21-44_patched/mm/madvise.c
    @@ -893,16 +893,24 @@ static int madvise_inject_error(int behavior,
    */
    size = page_size(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(pfn, MF_COUNT_INCREASED);
    + ret = soft_offline_page(pfn, 0);
    if (ret)
    return ret;
    continue;
    @@ -910,14 +918,6 @@ 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;
    --
    2.17.1
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