==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff868764c0 of 8 bytes by task 16811 on cpu 1:
 data_alloc+0x280/0x2e0 kernel/printk/printk_ringbuffer.c:1102
 prb_reserve+0x807/0xaf0 kernel/printk/printk_ringbuffer.c:1685
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 validate_nla lib/nlattr.c:414 [inline]
 __nla_validate_parse+0x1227/0x1d00 lib/nlattr.c:635
 __nla_parse+0x40/0x60 lib/nlattr.c:732
 nla_parse_nested_deprecated include/net/netlink.h:1379 [inline]
 rtnl_newlink+0x793/0x12d0 net/core/rtnetlink.c:4012
 rtnetlink_rcv_msg+0x5fe/0x6d0 net/core/rtnetlink.c:6951
 netlink_rcv_skb+0x123/0x220 net/netlink/af_netlink.c:2552
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6978
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5c0/0x690 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x58b/0x6b0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x145/0x180 net/socket.c:742
 ____sys_sendmsg+0x345/0x4e0 net/socket.c:2630
 ___sys_sendmsg+0x17b/0x1d0 net/socket.c:2684
 __sys_sendmmsg+0x178/0x300 net/socket.c:2773
 __do_sys_sendmmsg net/socket.c:2800 [inline]
 __se_sys_sendmmsg net/socket.c:2797 [inline]
 __x64_sys_sendmmsg+0x57/0x70 net/socket.c:2797
 x64_sys_call+0x1c4a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff868764c0 of 8 bytes by task 31 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:479 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:775 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:921 [inline]
 prb_reserve+0x220/0xaf0 kernel/printk/printk_ringbuffer.c:1635
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 dev_vprintk_emit+0x242/0x2a0 drivers/base/core.c:4914
 dev_printk_emit+0x84/0xb0 drivers/base/core.c:4925
 __netdev_printk+0x35c/0x3e0 net/core/dev.c:12716
 netdev_info+0x9b/0xd0 net/core/dev.c:12771
 nsim_udp_tunnel_set_port+0x13b/0x160 drivers/net/netdevsim/udp_tunnels.c:31
 udp_tunnel_nic_device_sync_one net/ipv4/udp_tunnel_nic.c:-1 [inline]
 udp_tunnel_nic_device_sync_by_port net/ipv4/udp_tunnel_nic.c:249 [inline]
 __udp_tunnel_nic_device_sync+0x567/0x9c0 net/ipv4/udp_tunnel_nic.c:292
 udp_tunnel_nic_device_sync_work+0x5d/0x5f0 net/ipv4/udp_tunnel_nic.c:740
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3346
 worker_thread+0x582/0x770 kernel/workqueue.c:3427
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x122/0x1b0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0xfffffffffffecd78 -> 0x00000000000a17e0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 31 Comm: kworker/u8:1 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: udp_tunnel_nic udp_tunnel_nic_device_sync_work
==================================================================
netdevsim netdevsim1 netdevsim0: set [0, 0] type 1 family 0 port 2816 - 0
netdevsim netdevsim1 netdevsim1: set [0, 0] type 1 family 0 port 2816 - 0
netdevsim netdevsim1 netdevsim2: set [0, 0] type 1 family 0 port 2816 - 0
netdevsim netdevsim1 netdevsim3: set [0, 0] type 1 family 0 port 2816 - 0