[net v3] net: wwan: t7xx: Fix napi rx poll issue

Jinjian Song
2025-05-30T03:21:25Z

When driver handles the napi rx polling requests, the netdev might
have been released by the dellink logic triggered by the disconnect
operation on user plane. However, in the logic of processing skb in
polling, an invalid netdev is still being used, which causes a panic.

BUG: kernel NULL pointer dereference, address: 00000000000000f1
Oops: 0000 [#1] PREEMPT SMP NOPTI
RIP: 0010:dev_gro_receive+0x3a/0x620
[...]
Call Trace:
<IRQ>
? __die_body+0x68/0xb0
? page_fault_oops+0x379/0x3e0
? exc_page_fault+0x4f/0xa0
? asm_exc_page_fault+0x22/0x30
? __pfx_t7xx_ccmni_recv_skb+0x10/0x10 [mtk_t7xx (HASH:1400 7)]
? dev_gro_receive+0x3a/0x620
napi_gro_receive+0xad/0x170
t7xx_ccmni_recv_skb+0x48/0x70 [mtk_t7xx (HASH:1400 7)]
t7xx_dpmaif_napi_rx_poll+0x590/0x800 [mtk_t7xx (HASH:1400 7)]
net_rx_action+0x103/0x470
irq_exit_rcu+0x13a/0x310
sysvec_apic_timer_interrupt+0x56/0x90
</IRQ>

Fixes: 5545b7b9f294 ("net: wwan: t7xx: Add NAPI support")
Signed-off-by: Jinjian Song <jinjian.song@fibocom.com>
---
v3:
* Only Use READ_ONCE/WRITE_ONCE when the lock protecting ctlb->ccmni_inst
is not held.
---
drivers/net/wwan/t7xx/t7xx_netdev.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wwan/t7xx/t7xx_netdev.c b/drivers/net/wwan/t7xx/t7xx_netdev.c
index 91fa082e9cab..fc0a7cb181df 100644
--- a/drivers/net/wwan/t7xx/t7xx_netdev.c
+++ b/drivers/net/wwan/t7xx/t7xx_netdev.c
@@ -302,7 +302,7 @@ static int t7xx_ccmni_wwan_newlink(void *ctxt, struct net_device *dev, u32 if_id
ccmni->ctlb = ctlb;
ccmni->dev = dev;
atomic_set(&ccmni->usage, 0);
- ctlb->ccmni_inst[if_id] = ccmni;
+ WRITE_ONCE(ctlb->ccmni_inst[if_id], ccmni);

ret = register_netdevice(dev);
if (ret)
@@ -324,6 +324,7 @@ static void t7xx_ccmni_wwan_dellink(void *ctxt, struct net_device *dev, struct l
if (WARN_ON(ctlb->ccmni_inst[if_id] != ccmni))
return;

+ WRITE_ONCE(ctlb->ccmni_inst[if_id], NULL);
unregister_netdevice(dev);
}

@@ -419,7 +420,7 @@ static void t7xx_ccmni_recv_skb(struct t7xx_ccmni_ctrl *ccmni_ctlb, struct sk_bu

skb_cb = T7XX_SKB_CB(skb);
netif_id = skb_cb->netif_idx;
- ccmni = ccmni_ctlb->ccmni_inst[netif_id];
+ ccmni = READ_ONCE(ccmni_ctlb->ccmni_inst[netif_id]);
if (!ccmni) {
dev_kfree_skb(skb);
return;
@@ -441,7 +442,7 @@ static void t7xx_ccmni_recv_skb(struct t7xx_ccmni_ctrl *ccmni_ctlb, struct sk_bu

static void t7xx_ccmni_queue_tx_irq_notify(struct t7xx_ccmni_ctrl *ctlb, int qno)
{
- struct t7xx_ccmni *ccmni = ctlb->ccmni_inst[0];
+ struct t7xx_ccmni *ccmni = READ_ONCE(ctlb->ccmni_inst[0]);
struct netdev_queue *net_queue;

if (netif_running(ccmni->dev) && atomic_read(&ccmni->usage) > 0) {
@@ -453,7 +454,7 @@ static void t7xx_ccmni_queue_tx_irq_notify(struct t7xx_ccmni_ctrl *ctlb, int qno

static void t7xx_ccmni_queue_tx_full_notify(struct t7xx_ccmni_ctrl *ctlb, int qno)
{
- struct t7xx_ccmni *ccmni = ctlb->ccmni_inst[0];
+ struct t7xx_ccmni *ccmni = READ_ONCE(ctlb->ccmni_inst[0]);
struct netdev_queue *net_queue;

if (atomic_read(&ccmni->usage) > 0) {
@@ -471,7 +472,7 @@ static void t7xx_ccmni_queue_state_notify(struct t7xx_pci_dev *t7xx_dev,
if (ctlb->md_sta != MD_STATE_READY)
return;

- if (!ctlb->ccmni_inst[0]) {
+ if (!READ_ONCE(ctlb->ccmni_inst[0])) {
dev_warn(&t7xx_dev->pdev->dev, "No netdev registered yet\n");
return;
}
--
2.34.1