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    Subject[PATCH 4.7 054/143] uprobes: Fix the memcg accounting
    Date
    4.7-stable review patch.  If anyone has any objections, please let me know.

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

    From: Oleg Nesterov <oleg@redhat.com>

    commit 6c4687cc17a788a6dd8de3e27dbeabb7cbd3e066 upstream.

    __replace_page() wronlgy calls mem_cgroup_cancel_charge() in "success" path,
    it should only do this if page_check_address() fails.

    This means that every enable/disable leads to unbalanced mem_cgroup_uncharge()
    from put_page(old_page), it is trivial to underflow the page_counter->count
    and trigger OOM.

    Reported-and-tested-by: Brenden Blanco <bblanco@plumgrid.com>
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
    Acked-by: Michal Hocko <mhocko@kernel.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
    Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
    Fixes: 00501b531c47 ("mm: memcontrol: rewrite charge API")
    Link: http://lkml.kernel.org/r/20160817153629.GB29724@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/events/uprobes.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/kernel/events/uprobes.c
    +++ b/kernel/events/uprobes.c
    @@ -172,8 +172,10 @@ static int __replace_page(struct vm_area
    mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
    err = -EAGAIN;
    ptep = page_check_address(page, mm, addr, &ptl, 0);
    - if (!ptep)
    + if (!ptep) {
    + mem_cgroup_cancel_charge(kpage, memcg, false);
    goto unlock;
    + }

    get_page(kpage);
    page_add_new_anon_rmap(kpage, vma, addr, false);
    @@ -200,7 +202,6 @@ static int __replace_page(struct vm_area

    err = 0;
    unlock:
    - mem_cgroup_cancel_charge(kpage, memcg, false);
    mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
    unlock_page(page);
    return err;

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