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    Subject[ 24/84] pkt_sched: fix virtual-start-time update in QFQ
    Date
    3.0-stable review patch.  If anyone has any objections, please let me know.

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


    From: Paolo Valente <paolo.valente@unimore.it>

    [ Upstream commit 71261956973ba9e0637848a5adb4a5819b4bae83 ]

    If the old timestamps of a class, say cl, are stale when the class
    becomes active, then QFQ may assign to cl a much higher start time
    than the maximum value allowed. This may happen when QFQ assigns to
    the start time of cl the finish time of a group whose classes are
    characterized by a higher value of the ratio
    max_class_pkt/weight_of_the_class with respect to that of
    cl. Inserting a class with a too high start time into the bucket list
    corrupts the data structure and may eventually lead to crashes.
    This patch limits the maximum start time assigned to a class.

    Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/sched/sch_qfq.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/net/sched/sch_qfq.c
    +++ b/net/sched/sch_qfq.c
    @@ -829,7 +829,10 @@ static void qfq_update_start(struct qfq_
    if (mask) {
    struct qfq_group *next = qfq_ffs(q, mask);
    if (qfq_gt(roundedF, next->F)) {
    - cl->S = next->F;
    + if (qfq_gt(limit, next->F))
    + cl->S = next->F;
    + else /* preserve timestamp correctness */
    + cl->S = limit;
    return;
    }
    }



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