Re: [PATCH net 1/3] igb: check __IGB_DOWN in igb_clean_rx_irq_zc()

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Fri, Mar 06, 2026 at 10:13:08PM +0100, Alex Dvoretsky wrote:
> When an AF_XDP zero-copy application terminates abruptly (e.g.,
> kill -9), the XSK buffer pool is destroyed but NAPI polling continues.
> igb_clean_rx_irq_zc() repeatedly returns the full budget (no
> descriptors, no buffers to allocate, xsk_buff_alloc() returns NULL)
> which makes napi_complete_done() re-arm the poll indefinitely.
> 
> Meanwhile igb_down() calls napi_synchronize(), which waits for a NAPI
> poll cycle that completes with done < budget. This never happens, so
> igb_down() blocks indefinitely. The 5-second TX watchdog fires because
> no TX completions are processed while NAPI is stuck. Since igb_down()
> never finishes, igb_up() is never called, and the TX queue remains
> permanently stalled.
> 
> Fix this by adding an __IGB_DOWN check at the top of
> igb_clean_rx_irq_zc(), returning 0 immediately when the adapter is
> going down. This allows napi_synchronize() in igb_down() to complete,
> matching the pattern already used in igb_clean_tx_irq().

How about getting rid of napi_synchronize() instead of hurting hot path?

napi_disable() sets NAPI_STATE_DISABLE which should prevent further polls
for you. Did you try that approach?

> 
> Fixes: 2c6196013f84 ("igb: Add AF_XDP zero-copy Rx support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alex Dvoretsky <advoretsky@gmail.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_xsk.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_xsk.c b/drivers/net/ethernet/intel/igb/igb_xsk.c
> index 30ce5fbb5b77..ca4aa4d935d5 100644
> --- a/drivers/net/ethernet/intel/igb/igb_xsk.c
> +++ b/drivers/net/ethernet/intel/igb/igb_xsk.c
> @@ -351,6 +351,9 @@ int igb_clean_rx_irq_zc(struct igb_q_vector *q_vector,
>  	u16 entries_to_alloc;
>  	struct sk_buff *skb;
>  
> +	if (test_bit(__IGB_DOWN, &adapter->state))
> +		return 0;
> +
>  	/* xdp_prog cannot be NULL in the ZC path */
>  	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
>  
> -- 
> 2.51.0
>