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    Subject[PATCH 4.19 090/114] net: ena: fix napi handler misbehavior when the napi budget is zero
    Date
    From: Netanel Belgazal <netanel@amazon.com>

    [ Upstream commit 24dee0c7478d1a1e00abdf5625b7f921467325dc ]

    In netpoll the napi handler could be called with budget equal to zero.
    Current ENA napi handler doesn't take that into consideration.

    The napi handler handles Rx packets in a do-while loop.
    Currently, the budget check happens only after decrementing the
    budget, therefore the napi handler, in rare cases, could run over
    MAX_INT packets.

    In addition to that, this moves all budget related variables to int
    calculation and stop mixing u32 to avoid ambiguity

    Fixes: 1738cd3ed342 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
    Signed-off-by: Netanel Belgazal <netanel@amazon.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/ethernet/amazon/ena/ena_netdev.c | 10 +++++++---
    1 file changed, 7 insertions(+), 3 deletions(-)

    --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
    +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
    @@ -1197,8 +1197,8 @@ static int ena_io_poll(struct napi_struc
    struct ena_napi *ena_napi = container_of(napi, struct ena_napi, napi);
    struct ena_ring *tx_ring, *rx_ring;

    - u32 tx_work_done;
    - u32 rx_work_done;
    + int tx_work_done;
    + int rx_work_done = 0;
    int tx_budget;
    int napi_comp_call = 0;
    int ret;
    @@ -1215,7 +1215,11 @@ static int ena_io_poll(struct napi_struc
    }

    tx_work_done = ena_clean_tx_irq(tx_ring, tx_budget);
    - rx_work_done = ena_clean_rx_irq(rx_ring, napi, budget);
    + /* On netpoll the budget is zero and the handler should only clean the
    + * tx completions.
    + */
    + if (likely(budget))
    + rx_work_done = ena_clean_rx_irq(rx_ring, napi, budget);

    /* If the device is about to reset or down, avoid unmask
    * the interrupt and return 0 so NAPI won't reschedule

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