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

write to 0xffffffff866956e8 of 8 bytes by task 12863 on cpu 0:
 prb_reserve+0x740/0xb60
 vprintk_store+0x558/0x870 kernel/printk/printk.c:2326
 vprintk_emit+0x15e/0x680 kernel/printk/printk.c:2408
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2447
 vprintk+0x75/0x80 kernel/printk/printk_safe.c:86
 _printk+0x7a/0xa0 kernel/printk/printk.c:2457
 __netdev_printk+0x2d1/0x3e0 net/core/dev.c:11825
 netdev_info+0x99/0xc0 net/core/dev.c:11872
 tun_net_xmit+0x46c/0xa90 drivers/net/tun.c:1087
 __netdev_start_xmit include/linux/netdevice.h:4928 [inline]
 netdev_start_xmit include/linux/netdevice.h:4937 [inline]
 xmit_one net/core/dev.c:3588 [inline]
 dev_hard_start_xmit+0x119/0x3f0 net/core/dev.c:3604
 sch_direct_xmit+0x1a9/0x580 net/sched/sch_generic.c:343
 __dev_xmit_skb net/core/dev.c:3825 [inline]
 __dev_queue_xmit+0xf1a/0x2040 net/core/dev.c:4398
 dev_queue_xmit include/linux/netdevice.h:3094 [inline]
 neigh_hh_output include/net/neighbour.h:526 [inline]
 neigh_output include/net/neighbour.h:540 [inline]
 ip_finish_output2+0x721/0x890 net/ipv4/ip_output.c:236
 ip_finish_output+0x11a/0x2a0 net/ipv4/ip_output.c:324
 NF_HOOK_COND include/linux/netfilter.h:303 [inline]
 ip_output+0xab/0x170 net/ipv4/ip_output.c:434
 dst_output include/net/dst.h:450 [inline]
 ip_local_out net/ipv4/ip_output.c:130 [inline]
 ip_send_skb+0x116/0x140 net/ipv4/ip_output.c:1496
 udp_send_skb+0x6a6/0x9f0 net/ipv4/udp.c:984
 udp_sendmsg+0x1257/0x12f0 net/ipv4/udp.c:1272
 inet_sendmsg+0xaf/0xd0 net/ipv4/af_inet.c:853
 sock_sendmsg_nosec net/socket.c:711 [inline]
 __sock_sendmsg+0x102/0x180 net/socket.c:726
 ____sys_sendmsg+0x312/0x410 net/socket.c:2581
 ___sys_sendmsg net/socket.c:2635 [inline]
 __sys_sendmmsg+0x227/0x4b0 net/socket.c:2724
 __do_sys_sendmmsg net/socket.c:2751 [inline]
 __se_sys_sendmmsg net/socket.c:2748 [inline]
 __x64_sys_sendmmsg+0x57/0x70 net/socket.c:2748
 x64_sys_call+0x29aa/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff866956e8 of 8 bytes by task 3006 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1957 [inline]
 _prb_read_valid+0x3bb/0xba0 kernel/printk/printk_ringbuffer.c:2114
 prb_read_valid+0x3d/0x60 kernel/printk/printk_ringbuffer.c:2182
 syslog_print+0xfc/0x760 kernel/printk/printk.c:1633
 do_syslog+0x3a1/0x7f0 kernel/printk/printk.c:1785
 __do_sys_syslog kernel/printk/printk.c:1877 [inline]
 __se_sys_syslog kernel/printk/printk.c:1875 [inline]
 __x64_sys_syslog+0x43/0x50 kernel/printk/printk.c:1875
 x64_sys_call+0x29be/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000035 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3006 Comm: klogd Not tainted 6.12.0-syzkaller-01892-g8f7c8b88bda4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
==================================================================