linux-kernel - Re: [PATCH v3 net] net: enetc: do not transmit redirected XDP frames when the link is down

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Message-ID: <20251211114025.3gqkeh4drdcp2tv5@skbuf>
Date: Thu, 11 Dec 2025 13:40:25 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Wei Fang <wei.fang@....com>
Cc: claudiu.manoil@....com, xiaoning.wang@....com, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, ast@...nel.org, daniel@...earbox.net,
	hawk@...nel.org, john.fastabend@...il.com, sdf@...ichev.me,
	frank.li@....com, imx@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v3 net] net: enetc: do not transmit redirected XDP frames
 when the link is down

On Thu, Dec 11, 2025 at 10:09:19AM +0800, Wei Fang wrote:
> In the current implementation, the enetc_xdp_xmit() always transmits
> redirected XDP frames even if the link is down, but the frames cannot
> be transmitted from TX BD rings when the link is down, so the frames
> are still kept in the TX BD rings. If the XDP program is uninstalled,
> users will see the following warning logs.
> 
> fsl_enetc 0000:00:00.0 eno0: timeout for tx ring #6 clear
> 
> More worse, the TX BD ring cannot work properly anymore, because the
> HW PIR and CIR are not equal after the re-initialization of the TX
> BD ring. At this point, the BDs between CIR and PIR are invalid,
> which will cause a hardware malfunction.
> 
> Another reason is that there is internal context in the ring prefetch
> logic that will retain the state from the first incarnation of the ring
> and continue prefetching from the stale location when we re-initialize
> the ring. The internal context is only reset by an FLR. That is to say,
> for LS1028A ENETC, software cannot set the HW CIR and PIR when
> initializing the TX BD ring.
> 
> It does not make sense to transmit redirected XDP frames when the link is
> down. Add a link status check to prevent transmission in this condition.
> This fixes part of the issue, but more complex cases remain. For example,
> the TX BD ring may still contain unsent frames when the link goes down.
> Those situations require additional patches, which will build on this
> one.
> 
> Fixes: 9d2b68cc108d ("net: enetc: add support for XDP_REDIRECT")
> Signed-off-by: Wei Fang <wei.fang@....com>
> Reviewed-by: Frank Li <Frank.Li@....com>
> 
> ---

More patches to fix the other conditions are coming. I can confirm that
they do not render this one useless. xdp_ok_fwd_dev() only tests that
the device is administratively up.

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