Re: [PATCH v4 net 2/4] net: enetc: block concurrent XDP transmissions during ring reconfiguration

[Vladimir Oltean]

On Thu, Oct 10, 2024 at 05:20:54PM +0800, Wei Fang wrote:
> When testing the XDP_REDIRECT function on the LS1028A platform, we
> found a very reproducible issue that the Tx frames can no longer be
> sent out even if XDP_REDIRECT is turned off. Specifically, if there
> is a lot of traffic on Rx direction, when XDP_REDIRECT is turned on,
> the console may display some warnings like "timeout for tx ring #6
> clear", and all redirected frames will be dropped, the detailed log
> is as follows.
> 
> root@ls1028ardb:~# ./xdp-bench redirect eno0 eno2
> Redirecting from eno0 (ifindex 3; driver fsl_enetc) to eno2 (ifindex 4; driver fsl_enetc)
> [203.849809] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #5 clear
> [204.006051] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #6 clear
> [204.161944] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #7 clear
> eno0->eno2     1420505 rx/s       1420590 err,drop/s      0 xmit/s
>   xmit eno0->eno2    0 xmit/s     1420590 drop/s     0 drv_err/s     15.71 bulk-avg
> eno0->eno2     1420484 rx/s       1420485 err,drop/s      0 xmit/s
>   xmit eno0->eno2    0 xmit/s     1420485 drop/s     0 drv_err/s     15.71 bulk-avg
> 
> By analyzing the XDP_REDIRECT implementation of enetc driver, the
> driver will reconfigure Tx and Rx BD rings when a bpf program is
> installed or uninstalled, but there is no mechanisms to block the
> redirected frames when enetc driver reconfigures rings. Similarly,
> XDP_TX verdicts on received frames can also lead to frames being
> enqueued in the Tx rings. Because XDP ignores the state set by the
> netif_tx_wake_queue() API, so introduce the ENETC_TX_DOWN flag to
> suppress transmission of XDP frames.
> 
> Fixes: c33bfaf91c4c ("net: enetc: set up XDP program under enetc_reconfigure()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Wei Fang <wei.fang@xxxxxxx>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>