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    Subject[PATCH 4.4 166/342] virtio_balloon: fix race by fill and leak
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Minchan Kim <minchan@kernel.org>

    commit f68b992bbb474641881932c61c92dcfa6f5b3689 upstream.

    During my compaction-related stuff, I encountered a bug
    with ballooning.

    With repeated inflating and deflating cycle, guest memory(
    ie, cat /proc/meminfo | grep MemTotal) is decreased and
    couldn't be recovered.

    The reason is balloon_lock doesn't cover release_pages_balloon
    so struct virtio_balloon fields could be overwritten by race
    of fill_balloon(e,g, vb->*pfns could be critical).

    This patch fixes it in my test.

    Signed-off-by: Minchan Kim <minchan@kernel.org>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/virtio/virtio_balloon.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/virtio/virtio_balloon.c
    +++ b/drivers/virtio/virtio_balloon.c
    @@ -209,8 +209,8 @@ static unsigned leak_balloon(struct virt
    */
    if (vb->num_pfns != 0)
    tell_host(vb, vb->deflate_vq);
    - mutex_unlock(&vb->balloon_lock);
    release_pages_balloon(vb);
    + mutex_unlock(&vb->balloon_lock);
    return num_freed_pages;
    }
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