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    Subject[PATCH 4.4 22/74] hwpoison, memcg: forcibly uncharge LRU pages
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Michal Hocko <mhocko@suse.com>

    commit 18365225f0440d09708ad9daade2ec11275c3df9 upstream.

    Laurent Dufour has noticed that hwpoinsoned pages are kept charged. In
    his particular case he has hit a bad_page("page still charged to
    cgroup") when onlining a hwpoison page. While this looks like something
    that shouldn't happen in the first place because onlining hwpages and
    returning them to the page allocator makes only little sense it shows a
    real problem.

    hwpoison pages do not get freed usually so we do not uncharge them (at
    least not since commit 0a31bc97c80c ("mm: memcontrol: rewrite uncharge
    API")). Each charge pins memcg (since e8ea14cc6ead ("mm: memcontrol:
    take a css reference for each charged page")) as well and so the
    mem_cgroup and the associated state will never go away. Fix this leak
    by forcibly uncharging a LRU hwpoisoned page in delete_from_lru_cache().
    We also have to tweak uncharge_list because it cannot rely on zero ref
    count for these pages.

    [akpm@linux-foundation.org: coding-style fixes]
    Fixes: 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")
    Link: http://lkml.kernel.org/r/20170502185507.GB19165@dhcp22.suse.cz
    Signed-off-by: Michal Hocko <mhocko@suse.com>
    Reported-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
    Tested-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
    Reviewed-by: Balbir Singh <bsingharora@gmail.com>
    Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/memcontrol.c | 2 +-
    mm/memory-failure.c | 7 +++++++
    2 files changed, 8 insertions(+), 1 deletion(-)

    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -5576,7 +5576,7 @@ static void uncharge_list(struct list_he
    next = page->lru.next;

    VM_BUG_ON_PAGE(PageLRU(page), page);
    - VM_BUG_ON_PAGE(page_count(page), page);
    + VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page);

    if (!page->mem_cgroup)
    continue;
    --- a/mm/memory-failure.c
    +++ b/mm/memory-failure.c
    @@ -539,6 +539,13 @@ static int delete_from_lru_cache(struct
    */
    ClearPageActive(p);
    ClearPageUnevictable(p);
    +
    + /*
    + * Poisoned page might never drop its ref count to 0 so we have
    + * to uncharge it manually from its memcg.
    + */
    + mem_cgroup_uncharge(p);
    +
    /*
    * drop the page count elevated by isolate_lru_page()
    */

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