[PATCH net] net: lan966x: don't disable hardirqs in fdma tx clear path

[Daniel Machon]

lan966x_fdma_tx_clear_buf() runs from the NAPI poll and frees the
buffers of completed tx DCBs with napi_consume_skb(),
page_pool_recycle_direct() and xdp_return_frame_bulk(), under
lan966x->tx_lock.

Before this patch, the lock is taken with spin_lock_irqsave(), so the
buffers are freed with hardirqs disabled. RX skbs are marked for
page_pool recycling, so when such an skb is forwarded back out and its
tx completion frees it here, the free path reaches __page_pool_put_page(),
which warns via lockdep_assert_no_hardirq().

Take tx_lock with a plain spin_lock(), as the other tx_lock users,
lan966x_port_xmit() and lan966x_fdma_xmit_xdpf(), already do.
tx_clear_buf() runs from the NAPI poll, so disabling hardirqs there is
not needed.

Found with lockdep enabled (CONFIG_PROVE_LOCKING), which the assert
depends on. Reproduced on a lan9668 board by redirecting received frames
out of another port with tc mirred.

Fixes: 11871aba1974 ("net: lan96x: Use page_pool API")
Signed-off-by: Daniel Machon <daniel.machon@xxxxxxxxxxxxx>
---
 drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index a7940eca5df31..a92bd0590b460 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -336,14 +336,13 @@ static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
 	struct lan966x_tx_dcb_buf *dcb_buf;
 	struct fdma *fdma = &tx->fdma;
 	struct xdp_frame_bulk bq;
-	unsigned long flags;
 	bool clear = false;
 	struct fdma_db *db;
 	int i;
 
 	xdp_frame_bulk_init(&bq);
 
-	spin_lock_irqsave(&lan966x->tx_lock, flags);
+	spin_lock(&lan966x->tx_lock);
 	for (i = 0; i < fdma->n_dcbs; ++i) {
 		dcb_buf = &tx->dcbs_buf[i];
 
@@ -388,7 +387,7 @@ static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
 	if (clear)
 		lan966x_fdma_wakeup_netdev(lan966x);
 
-	spin_unlock_irqrestore(&lan966x->tx_lock, flags);
+	spin_unlock(&lan966x->tx_lock);
 }
 
 static int lan966x_fdma_rx_check_frame(struct lan966x_rx *rx, u64 *src_port)

---
base-commit: 6430fb7f1cc4e329e386521b7b208df443de92f2
change-id: 20261023-lan966x-fdma-tx-clear-hardirq-43724a086d0d

Best regards,
-- 
Daniel Machon <daniel.machon@xxxxxxxxxxxxx>