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    Subject[GIT PULL for-4.4 06/25] net/mlx4_en: fix overflow in mlx4_en_init_timestamp()
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 47d3a07528ecbbccf53bc4390d70b4e3d1c04fcf ]

    The cited commit makes a great job of finding optimal shift/multiplier
    values assuming a 10 seconds wrap around, but forgot to change the
    overflow_period computation.

    It overflows in cyclecounter_cyc2ns(), and the final result is 804 ms,
    which is silly.

    Lets simply use 5 seconds, no need to recompute this, given how it is
    supposed to work.

    Later, we will use a timer instead of a work queue, since the new RX
    allocation schem will no longer need mlx4_en_recover_from_oom() and the
    service_task firing every 250 ms.

    Fixes: 31c128b66e5b ("net/mlx4_en: Choose time-stamping shift value according to HW frequency")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Tariq Toukan <tariqt@mellanox.com>
    Cc: Eugenia Emantayev <eugenia@mellanox.com>
    Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    ---
    drivers/net/ethernet/mellanox/mlx4/en_clock.c | 18 ++++++++----------
    drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 1 -
    2 files changed, 8 insertions(+), 11 deletions(-)

    diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
    index 1494997c4f7e..4dccf7287f0f 100644
    --- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
    +++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
    @@ -88,10 +88,17 @@ void mlx4_en_remove_timestamp(struct mlx4_en_dev *mdev)
    }
    }

    +#define MLX4_EN_WRAP_AROUND_SEC 10UL
    +/* By scheduling the overflow check every 5 seconds, we have a reasonably
    + * good chance we wont miss a wrap around.
    + * TOTO: Use a timer instead of a work queue to increase the guarantee.
    + */
    +#define MLX4_EN_OVERFLOW_PERIOD (MLX4_EN_WRAP_AROUND_SEC * HZ / 2)
    +
    void mlx4_en_ptp_overflow_check(struct mlx4_en_dev *mdev)
    {
    bool timeout = time_is_before_jiffies(mdev->last_overflow_check +
    - mdev->overflow_period);
    + MLX4_EN_OVERFLOW_PERIOD);
    unsigned long flags;

    if (timeout) {
    @@ -236,7 +243,6 @@ static const struct ptp_clock_info mlx4_en_ptp_clock_info = {
    .enable = mlx4_en_phc_enable,
    };

    -#define MLX4_EN_WRAP_AROUND_SEC 10ULL

    /* This function calculates the max shift that enables the user range
    * of MLX4_EN_WRAP_AROUND_SEC values in the cycles register.
    @@ -258,7 +264,6 @@ void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
    {
    struct mlx4_dev *dev = mdev->dev;
    unsigned long flags;
    - u64 ns, zero = 0;

    /* mlx4_en_init_timestamp is called for each netdev.
    * mdev->ptp_clock is common for all ports, skip initialization if
    @@ -282,13 +287,6 @@ void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
    ktime_to_ns(ktime_get_real()));
    write_unlock_irqrestore(&mdev->clock_lock, flags);

    - /* Calculate period in seconds to call the overflow watchdog - to make
    - * sure counter is checked at least once every wrap around.
    - */
    - ns = cyclecounter_cyc2ns(&mdev->cycles, mdev->cycles.mask, zero, &zero);
    - do_div(ns, NSEC_PER_SEC / 2 / HZ);
    - mdev->overflow_period = ns;
    -
    /* Configure the PHC */
    mdev->ptp_clock_info = mlx4_en_ptp_clock_info;
    snprintf(mdev->ptp_clock_info.name, 16, "mlx4 ptp");
    diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
    index c41f15102ae0..10aa6544cf4d 100644
    --- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
    +++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
    @@ -409,7 +409,6 @@ struct mlx4_en_dev {
    struct cyclecounter cycles;
    struct timecounter clock;
    unsigned long last_overflow_check;
    - unsigned long overflow_period;
    struct ptp_clock *ptp_clock;
    struct ptp_clock_info ptp_clock_info;
    struct notifier_block nb;
    --
    2.11.0
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