[PATCH net v2 2/3] net: ti: icssg-prueth: Fix kernel panic during concurrent Tx queue access

[Meghana Malladi]

Add __netif_tx_lock() to ensure that only one packet is being
transmitted at a time to avoid race conditions in the netif_txq
struct and prevent packet data corruption. Failing to do so causes
kernel panic with the following error:

[ 2184.746764] ------------[ cut here ]------------
[ 2184.751412] kernel BUG at lib/dynamic_queue_limits.c:99!
[ 2184.756728] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP

logs: https://gist.github.com/MeghanaMalladiTI/9c7aa5fc3b7fb03f87c74aad487956e9

The lock is acquired before calling emac_xmit_xdp_frame() and released after the
call returns. This ensures that the TX queue is protected from concurrent access
during the transmission of XDP frames.

Fixes: 62aa3246f462 ("net: ti: icssg-prueth: Add XDP support")
Signed-off-by: Meghana Malladi <m-malladi at ti.com>
---

Changes from v1 (v2-v1):
- Move netif_tx_lock/unlock outside of the loop, reported by Jesper Dangaard Brouer <hawk at kernel.org>

 drivers/net/ethernet/ti/icssg/icssg_common.c | 7 ++++++-
 drivers/net/ethernet/ti/icssg/icssg_prueth.c | 7 ++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/ti/icssg/icssg_common.c b/drivers/net/ethernet/ti/icssg/icssg_common.c
index 79f2d86acf21..36d5cb25c017 100644
--- a/drivers/net/ethernet/ti/icssg/icssg_common.c
+++ b/drivers/net/ethernet/ti/icssg/icssg_common.c
@@ -650,6 +650,8 @@ static u32 emac_run_xdp(struct prueth_emac *emac, struct xdp_buff *xdp,
 			struct page *page, u32 *len)
 {
 	struct net_device *ndev = emac->ndev;
+	struct netdev_queue *netif_txq;
+	int cpu = smp_processor_id();
 	struct bpf_prog *xdp_prog;
 	struct xdp_frame *xdpf;
 	u32 pkt_len = *len;
@@ -669,8 +671,11 @@ static u32 emac_run_xdp(struct prueth_emac *emac, struct xdp_buff *xdp,
 			goto drop;
 		}
 
-		q_idx = smp_processor_id() % emac->tx_ch_num;
+		q_idx = cpu % emac->tx_ch_num;
+		netif_txq = netdev_get_tx_queue(ndev, q_idx);
+		__netif_tx_lock(netif_txq, cpu);
 		result = emac_xmit_xdp_frame(emac, xdpf, page, q_idx);
+		__netif_tx_unlock(netif_txq);
 		if (result == ICSSG_XDP_CONSUMED) {
 			ndev->stats.tx_dropped++;
 			goto drop;
diff --git a/drivers/net/ethernet/ti/icssg/icssg_prueth.c b/drivers/net/ethernet/ti/icssg/icssg_prueth.c
index ee35fecf61e7..86fc1278127c 100644
--- a/drivers/net/ethernet/ti/icssg/icssg_prueth.c
+++ b/drivers/net/ethernet/ti/icssg/icssg_prueth.c
@@ -1075,17 +1075,21 @@ static int emac_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frame
 {
 	struct prueth_emac *emac = netdev_priv(dev);
 	struct net_device *ndev = emac->ndev;
+	struct netdev_queue *netif_txq;
+	int cpu = smp_processor_id();
 	struct xdp_frame *xdpf;
 	unsigned int q_idx;
 	int nxmit = 0;
 	u32 err;
 	int i;
 
-	q_idx = smp_processor_id() % emac->tx_ch_num;
+	q_idx = cpu % emac->tx_ch_num;
+	netif_txq = netdev_get_tx_queue(ndev, q_idx);
 
 	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
 		return -EINVAL;
 
+	__netif_tx_lock(netif_txq, cpu);
 	for (i = 0; i < n; i++) {
 		xdpf = frames[i];
 		err = emac_xmit_xdp_frame(emac, xdpf, NULL, q_idx);
@@ -1095,6 +1099,7 @@ static int emac_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frame
 		}
 		nxmit++;
 	}
+	__netif_tx_unlock(netif_txq);
 
 	return nxmit;
 }
-- 
2.43.0