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

[Alex Dvoretsky <advoretsky@gmail.com>]

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().

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