Subject: [PATCH v2] usbnet: Fix using smp_processor_id() in preemptible code warnings

From: Zqiang <[email-masked]>
Date: Sat, 11 Oct 2025 15:05:18 +0800

Syzbot reported the following warning:

BUG: using smp_processor_id() in preemptible [00000000] code: dhcpcd/2879
caller is usbnet_skb_return+0x74/0x490 drivers/net/usb/usbnet.c:331
CPU: 1 UID: 0 PID: 2879 Comm: dhcpcd Not tainted 6.15.0-rc4-syzkaller-00098-g615dca38c2ea #0 PREEMPT(voluntary)
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
 check_preemption_disabled+0xd0/0xe0 lib/smp_processor_id.c:49
 usbnet_skb_return+0x74/0x490 drivers/net/usb/usbnet.c:331
 usbnet_resume_rx+0x4b/0x170 drivers/net/usb/usbnet.c:708
 usbnet_change_mtu+0x1be/0x220 drivers/net/usb/usbnet.c:417
 __dev_set_mtu net/core/dev.c:9443 [inline]
 netif_set_mtu_ext+0x369/0x5c0 net/core/dev.c:9496
 netif_set_mtu+0xb0/0x160 net/core/dev.c:9520
 dev_set_mtu+0xae/0x170 net/core/dev_api.c:247
 dev_ifsioc+0xa31/0x18d0 net/core/dev_ioctl.c:572
 dev_ioctl+0x223/0x10e0 net/core/dev_ioctl.c:821
 sock_do_ioctl+0x19d/0x280 net/socket.c:1204
 sock_ioctl+0x42f/0x6a0 net/socket.c:1311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl fs/ioctl.c:892 [inline]
 __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

For historical and portability reasons, the netif_rx() is usually
run in the softirq or interrupt context, this commit therefore add
local_bh_disable/enable() protection in the usbnet_resume_rx().

Fixes: 43daa96b166c ("usbnet: Stop RX Q on MTU change")
Link: https://syzkaller.appspot.com/bug?id=81f55dfa587ee544baaaa5a359a060512228c1e1
Suggested-by: Jakub Kicinski <[email-masked]>
Signed-off-by: Zqiang <[email-masked]>
---
 v1->v2
 Use BH-disable protection in usbnet_resume_rx() instead of using
 get_cpu_ptr(dev->net->tstats) in usbnet_skb_return().

 drivers/net/usb/usbnet.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 511c4154cf74..bf01f2728531 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -702,6 +702,7 @@ void usbnet_resume_rx(struct usbnet *dev)
 	struct sk_buff *skb;
 	int num = 0;
 
+	local_bh_disable();
 	clear_bit(EVENT_RX_PAUSED, &dev->flags);
 
 	while ((skb = skb_dequeue(&dev->rxq_pause)) != NULL) {
@@ -710,6 +711,7 @@ void usbnet_resume_rx(struct usbnet *dev)
 	}
 
 	queue_work(system_bh_wq, &dev->bh_work);
+	local_bh_enable();
 
 	netif_dbg(dev, rx_status, dev->net,
 		  "paused rx queue disabled, %d skbs requeued\n", num);
-- 
2.17.1