netdev - Re: pegged softirq and NAPI race (?)

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Date:   Tue, 18 Sep 2018 14:13:25 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     songliubraving@...com
Cc:     Alexei Starovoitov <ast@...com>, netdev <netdev@...r.kernel.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        michael.chan@...adcom.com, kernel-team <Kernel-team@...com>
Subject: Re: pegged softirq and NAPI race (?)

On Tue, Sep 18, 2018 at 1:37 PM Song Liu <songliubraving@...com> wrote:
>

> Looks like a patch like the following fixes the issue for ixgbe. But I
> cannot explain it yet.
>
> Does this ring a bell?

I dunno, it looks like the NIC is  generating an interrupt while it should not,
and constantly sets NAPI_STATE_MISSED.

Or maybe we need to properly check napi_complete_done() return value.

diff --git a/drivers/net/ethernet/intel/ixgb/ixgb_main.c
b/drivers/net/ethernet/intel/ixgb/ixgb_main.c
index d3e72d0f66ef428b08e4bd88508e05b734bc43a4..c4c565c982a98a5891603cedcdcb72dc1c401813
100644
--- a/drivers/net/ethernet/intel/ixgb/ixgb_main.c
+++ b/drivers/net/ethernet/intel/ixgb/ixgb_main.c
@@ -1773,8 +1773,8 @@ ixgb_clean(struct napi_struct *napi, int budget)
        ixgb_clean_rx_irq(adapter, &work_done, budget);

        /* If budget not fully consumed, exit the polling mode */
-       if (work_done < budget) {
-               napi_complete_done(napi, work_done);
+       if (work_done < budget &&
+           napi_complete_done(napi, work_done)) {
                if (!test_bit(__IXGB_DOWN, &adapter->flags))
                        ixgb_irq_enable(adapter);
        }