Commit 50bd33f6 authored by Jianpeng Chang's avatar Jianpeng Chang Committed by Jakub Kicinski
Browse files

net: enetc: fix the deadlock of enetc_mdio_lock 



After applying the workaround for err050089, the LS1028A platform
experiences RCU stalls on RT kernel. This issue is caused by the
recursive acquisition of the read lock enetc_mdio_lock. Here list some
of the call stacks identified under the enetc_poll path that may lead to
a deadlock:

enetc_poll
  -> enetc_lock_mdio
  -> enetc_clean_rx_ring OR napi_complete_done
     -> napi_gro_receive
        -> enetc_start_xmit
           -> enetc_lock_mdio
           -> enetc_map_tx_buffs
           -> enetc_unlock_mdio
  -> enetc_unlock_mdio

After enetc_poll acquires the read lock, a higher-priority writer attempts
to acquire the lock, causing preemption. The writer detects that a
read lock is already held and is scheduled out. However, readers under
enetc_poll cannot acquire the read lock again because a writer is already
waiting, leading to a thread hang.

Currently, the deadlock is avoided by adjusting enetc_lock_mdio to prevent
recursive lock acquisition.

Fixes: 6d36ecdb ("net: enetc: take the MDIO lock only once per NAPI poll cycle")
Signed-off-by: default avatarJianpeng Chang <jianpeng.chang.cn@windriver.com>
Acked-by: default avatarWei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20251015021427.180757-1-jianpeng.chang.cn@windriver.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 7f864458

drivers/net/ethernet/freescale/enetc/enetc.c

+21 −4
Original line number Diff line number Diff line
@@ -1595,6 +1595,8 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring, 
	/* next descriptor to process */

	i = rx_ring->next_to_clean;



	enetc_lock_mdio();



	while (likely(rx_frm_cnt < work_limit)) {

		union enetc_rx_bd *rxbd;

		struct sk_buff *skb;
@@ -1630,7 +1632,9 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring, 
		rx_byte_cnt += skb->len + ETH_HLEN;

		rx_frm_cnt++;



		enetc_unlock_mdio();

		napi_gro_receive(napi, skb);

		enetc_lock_mdio();

	}



	rx_ring->next_to_clean = i;
@@ -1638,6 +1642,8 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring, 
	rx_ring->stats.packets += rx_frm_cnt;

	rx_ring->stats.bytes += rx_byte_cnt;



	enetc_unlock_mdio();



	return rx_frm_cnt;

}
@@ -1947,6 +1953,8 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring, 
	/* next descriptor to process */

	i = rx_ring->next_to_clean;



	enetc_lock_mdio();



	while (likely(rx_frm_cnt < work_limit)) {

		union enetc_rx_bd *rxbd, *orig_rxbd;

		struct xdp_buff xdp_buff;
@@ -2010,7 +2018,9 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring, 
			 */

			enetc_bulk_flip_buff(rx_ring, orig_i, i);



			enetc_unlock_mdio();

			napi_gro_receive(napi, skb);

			enetc_lock_mdio();

			break;

		case XDP_TX:

			tx_ring = priv->xdp_tx_ring[rx_ring->index];
@@ -2045,7 +2055,9 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring, 
			}

			break;

		case XDP_REDIRECT:

			enetc_unlock_mdio();

			err = xdp_do_redirect(rx_ring->ndev, &xdp_buff, prog);

			enetc_lock_mdio();

			if (unlikely(err)) {

				enetc_xdp_drop(rx_ring, orig_i, i);

				rx_ring->stats.xdp_redirect_failures++;
@@ -2065,8 +2077,11 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring, 
	rx_ring->stats.packets += rx_frm_cnt;

	rx_ring->stats.bytes += rx_byte_cnt;



	if (xdp_redirect_frm_cnt)

	if (xdp_redirect_frm_cnt) {

		enetc_unlock_mdio();

		xdp_do_flush();

		enetc_lock_mdio();

	}



	if (xdp_tx_frm_cnt)

		enetc_update_tx_ring_tail(tx_ring);
@@ -2075,6 +2090,8 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring, 
		enetc_refill_rx_ring(rx_ring, enetc_bd_unused(rx_ring) -

				     rx_ring->xdp.xdp_tx_in_flight);



	enetc_unlock_mdio();



	return rx_frm_cnt;

}
@@ -2093,6 +2110,7 @@ static int enetc_poll(struct napi_struct *napi, int budget) 
	for (i = 0; i < v->count_tx_rings; i++)

		if (!enetc_clean_tx_ring(&v->tx_ring[i], budget))

			complete = false;

	enetc_unlock_mdio();



	prog = rx_ring->xdp.prog;

	if (prog)
@@ -2104,10 +2122,8 @@ static int enetc_poll(struct napi_struct *napi, int budget) 
	if (work_done)

		v->rx_napi_work = true;



	if (!complete) {

		enetc_unlock_mdio();

	if (!complete)

		return budget;

	}



	napi_complete_done(napi, work_done);
@@ -2116,6 +2132,7 @@ static int enetc_poll(struct napi_struct *napi, int budget) 


	v->rx_napi_work = false;



	enetc_lock_mdio();

	/* enable interrupts */

	enetc_wr_reg_hot(v->rbier, ENETC_RBIER_RXTIE);