[PATCH net v2 1/2] net: ethernet: mtk-star-emac: fix spinlock recursion issues on rx/tx poll

[Louis-Alexis Eyraud]

Use spin_lock_irqsave and spin_unlock_irqrestore instead of spin_lock
and spin_unlock in mtk_star_emac driver to avoid spinlock recursion
occurrence that can happen when enabling the DMA interrupts again in
rx/tx poll.

```
BUG: spinlock recursion on CPU#0, swapper/0/0
 lock: 0xffff00000db9cf20, .magic: dead4ead, .owner: swapper/0/0,
    .owner_cpu: 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted
    6.15.0-rc2-next-20250417-00001-gf6a27738686c-dirty #28 PREEMPT
Hardware name: MediaTek MT8365 Open Platform EVK (DT)
Call trace:
 show_stack+0x18/0x24 (C)
 dump_stack_lvl+0x60/0x80
 dump_stack+0x18/0x24
 spin_dump+0x78/0x88
 do_raw_spin_lock+0x11c/0x120
 _raw_spin_lock+0x20/0x2c
 mtk_star_handle_irq+0xc0/0x22c [mtk_star_emac]
 __handle_irq_event_percpu+0x48/0x140
 handle_irq_event+0x4c/0xb0
 handle_fasteoi_irq+0xa0/0x1bc
 handle_irq_desc+0x34/0x58
 generic_handle_domain_irq+0x1c/0x28
 gic_handle_irq+0x4c/0x120
 do_interrupt_handler+0x50/0x84
 el1_interrupt+0x34/0x68
 el1h_64_irq_handler+0x18/0x24
 el1h_64_irq+0x6c/0x70
 regmap_mmio_read32le+0xc/0x20 (P)
 _regmap_bus_reg_read+0x6c/0xac
 _regmap_read+0x60/0xdc
 regmap_read+0x4c/0x80
 mtk_star_rx_poll+0x2f4/0x39c [mtk_star_emac]
 __napi_poll+0x38/0x188
 net_rx_action+0x164/0x2c0
 handle_softirqs+0x100/0x244
 __do_softirq+0x14/0x20
 ____do_softirq+0x10/0x20
 call_on_irq_stack+0x24/0x64
 do_softirq_own_stack+0x1c/0x40
 __irq_exit_rcu+0xd4/0x10c
 irq_exit_rcu+0x10/0x1c
 el1_interrupt+0x38/0x68
 el1h_64_irq_handler+0x18/0x24
 el1h_64_irq+0x6c/0x70
 cpuidle_enter_state+0xac/0x320 (P)
 cpuidle_enter+0x38/0x50
 do_idle+0x1e4/0x260
 cpu_startup_entry+0x34/0x3c
 rest_init+0xdc/0xe0
 console_on_rootfs+0x0/0x6c
 __primary_switched+0x88/0x90
```

Fixes: 0a8bd81fd6aa ("net: ethernet: mtk-star-emac: separate tx/rx handling with two NAPIs")
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud at collabora.com>
---
 drivers/net/ethernet/mediatek/mtk_star_emac.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_star_emac.c b/drivers/net/ethernet/mediatek/mtk_star_emac.c
index 76f202d7f05537642ec294811ace2ad4a7eae383..23115881d8e892a622b34b593cf38e2c8bed4082 100644
--- a/drivers/net/ethernet/mediatek/mtk_star_emac.c
+++ b/drivers/net/ethernet/mediatek/mtk_star_emac.c
@@ -1163,6 +1163,7 @@ static int mtk_star_tx_poll(struct napi_struct *napi, int budget)
 	struct net_device *ndev = priv->ndev;
 	unsigned int head = ring->head;
 	unsigned int entry = ring->tail;
+	unsigned long flags;
 
 	while (entry != head && count < (MTK_STAR_RING_NUM_DESCS - 1)) {
 		ret = mtk_star_tx_complete_one(priv);
@@ -1182,9 +1183,9 @@ static int mtk_star_tx_poll(struct napi_struct *napi, int budget)
 		netif_wake_queue(ndev);
 
 	if (napi_complete(napi)) {
-		spin_lock(&priv->lock);
+		spin_lock_irqsave(&priv->lock, flags);
 		mtk_star_enable_dma_irq(priv, false, true);
-		spin_unlock(&priv->lock);
+		spin_unlock_irqrestore(&priv->lock, flags);
 	}
 
 	return 0;
@@ -1341,6 +1342,7 @@ static int mtk_star_rx(struct mtk_star_priv *priv, int budget)
 static int mtk_star_rx_poll(struct napi_struct *napi, int budget)
 {
 	struct mtk_star_priv *priv;
+	unsigned long flags;
 	int work_done = 0;
 
 	priv = container_of(napi, struct mtk_star_priv, rx_napi);
@@ -1348,9 +1350,9 @@ static int mtk_star_rx_poll(struct napi_struct *napi, int budget)
 	work_done = mtk_star_rx(priv, budget);
 	if (work_done < budget) {
 		napi_complete_done(napi, work_done);
-		spin_lock(&priv->lock);
+		spin_lock_irqsave(&priv->lock, flags);
 		mtk_star_enable_dma_irq(priv, true, false);
-		spin_unlock(&priv->lock);
+		spin_unlock_irqrestore(&priv->lock, flags);
 	}
 
 	return work_done;

-- 
2.49.0