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    Subject[PATCH AUTOSEL for 4.9 032/293] net: ena: fix rare uncompleted admin command false alarm
    Date
    From: Netanel Belgazal <netanel@amazon.com>

    [ Upstream commit a77c1aafcc906f657d1a0890c1d898be9ee1d5c9 ]

    The current flow to detect admin completion is:
    while (command_not_completed) {
    if (timeout)
    error

    check_for_completion()
    sleep()
    }
    So in case the sleep took more than the timeout
    (in case the thread/workqueue was not scheduled due to higher priority
    task or prolonged VMexit), the driver can detect a stall even if
    the completion is present.

    The fix changes the order of this function to first check for
    completion and only after that check if the timeout expired.

    Fixes: 1738cd3ed342 ("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: Sasha Levin <alexander.levin@microsoft.com>
    ---
    drivers/net/ethernet/amazon/ena/ena_com.c | 21 +++++++++++----------
    1 file changed, 11 insertions(+), 10 deletions(-)

    diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
    index e2512ab41168..564b556baba9 100644
    --- a/drivers/net/ethernet/amazon/ena/ena_com.c
    +++ b/drivers/net/ethernet/amazon/ena/ena_com.c
    @@ -508,15 +508,20 @@ static int ena_com_comp_status_to_errno(u8 comp_status)
    static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_ctx,
    struct ena_com_admin_queue *admin_queue)
    {
    - unsigned long flags;
    - u32 start_time;
    + unsigned long flags, timeout;
    int ret;

    - start_time = ((u32)jiffies_to_usecs(jiffies));
    + timeout = jiffies + ADMIN_CMD_TIMEOUT_US;
    +
    + while (1) {
    + spin_lock_irqsave(&admin_queue->q_lock, flags);
    + ena_com_handle_admin_completion(admin_queue);
    + spin_unlock_irqrestore(&admin_queue->q_lock, flags);

    - while (comp_ctx->status == ENA_CMD_SUBMITTED) {
    - if ((((u32)jiffies_to_usecs(jiffies)) - start_time) >
    - ADMIN_CMD_TIMEOUT_US) {
    + if (comp_ctx->status != ENA_CMD_SUBMITTED)
    + break;
    +
    + if (time_is_before_jiffies(timeout)) {
    pr_err("Wait for completion (polling) timeout\n");
    /* ENA didn't have any completion */
    spin_lock_irqsave(&admin_queue->q_lock, flags);
    @@ -528,10 +533,6 @@ static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_c
    goto err;
    }

    - spin_lock_irqsave(&admin_queue->q_lock, flags);
    - ena_com_handle_admin_completion(admin_queue);
    - spin_unlock_irqrestore(&admin_queue->q_lock, flags);
    -
    msleep(100);
    }

    --
    2.15.1
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