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    Subject[PATCH 3.16 126/294] net_sched: fix order of queue length updates in qdisc_replace()
    3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

    commit 68a66d149a8c78ec6720f268597302883e48e9fa upstream.

    This important to call qdisc_tree_reduce_backlog() after changing queue
    length. Parent qdisc should deactivate class in ->qlen_notify() called from
    qdisc_tree_reduce_backlog() but this happens only if qdisc->q.qlen in zero.

    Missed class deactivations leads to crashes/warnings at picking packets
    from empty qdisc and corrupting state at reactivating this class in future.

    Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
    Fixes: 86a7996cc8a0 ("net_sched: introduce qdisc_replace() helper")
    Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    include/net/sch_generic.h | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/include/net/sch_generic.h
    +++ b/include/net/sch_generic.h
    @@ -618,8 +618,11 @@ static inline struct Qdisc *qdisc_replac
    old = *pold;
    *pold = new;
    if (old != NULL) {
    - qdisc_tree_reduce_backlog(old, old->q.qlen, old->qstats.backlog);
    + unsigned int qlen = old->q.qlen;
    + unsigned int backlog = old->qstats.backlog;
    +
    qdisc_reset(old);
    + qdisc_tree_reduce_backlog(old, qlen, backlog);
    }
    sch_tree_unlock(sch);

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