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

write to 0xffffffff86f1eab8 of 88 bytes by task 3286 on cpu 0:
 prb_reserve+0x6fb/0xaf0 kernel/printk/printk_ringbuffer.c:1693
 vprintk_store+0x54e/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x610 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 nf_log_buf_close+0x42/0xa0 net/netfilter/nf_log.c:336
 nf_log_ip_packet+0x11d/0x140 net/netfilter/nf_log_syslog.c:872
 nf_log_packet+0x155/0x190 net/netfilter/nf_log.c:260
 nft_log_eval+0x1a6/0x1d0 net/netfilter/nft_log.c:60
 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
 nft_do_chain+0x1ff/0xde0 net/netfilter/nf_tables_core.c:285
 nft_do_chain_ipv4+0x14e/0x180 net/netfilter/nft_chain_filter.c:24
 nf_hook_entry_hookfn include/linux/netfilter.h:165 [inline]
 nf_hook_slow+0x78/0x180 net/netfilter/core.c:619
 nf_hook include/linux/netfilter.h:280 [inline]
 __ip_local_out+0x2fd/0x320 net/ipv4/ip_output.c:120
 ip_local_out net/ipv4/ip_output.c:129 [inline]
 __ip_queue_xmit+0xa95/0xb80 net/ipv4/ip_output.c:533
 ip_queue_xmit+0x39/0x50 net/ipv4/ip_output.c:547
 __tcp_transmit_skb+0x1c4f/0x20f0 net/ipv4/tcp_output.c:1717
 tcp_transmit_skb net/ipv4/tcp_output.c:1734 [inline]
 tcp_write_xmit+0x17f7/0x3630 net/ipv4/tcp_output.c:3062
 __tcp_push_pending_frames+0x6d/0x1b0 net/ipv4/tcp_output.c:3245
 tcp_push_pending_frames include/net/tcp.h:2341 [inline]
 tcp_data_snd_check net/ipv4/tcp_input.c:6108 [inline]
 tcp_rcv_established+0xdf3/0x1360 net/ipv4/tcp_input.c:6592
 tcp_v4_do_rcv+0x3b1/0xa20 net/ipv4/tcp_ipv4.c:1854
 sk_backlog_rcv include/net/sock.h:1192 [inline]
 __release_sock+0x146/0x2d0 net/core/sock.c:3270
 release_sock+0x125/0x180 net/core/sock.c:3869
 tcp_sendmsg+0x39/0x50 net/ipv4/tcp.c:1452
 inet_sendmsg+0x76/0xd0 net/ipv4/af_inet.c:865
 sock_sendmsg_nosec net/socket.c:801 [inline]
 __sock_sendmsg net/socket.c:815 [inline]
 sock_write_iter+0x2a4/0x2f0 net/socket.c:1266
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x57f/0x9a0 fs/read_write.c:687
 ksys_write+0xdc/0x1a0 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:747
 x64_sys_call+0x154e/0x2550 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86f1eab8 of 8 bytes by task 32372 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:2017 [inline]
 _prb_read_valid+0x325/0x930 kernel/printk/printk_ringbuffer.c:2174
 prb_first_valid_seq+0x35/0x70 kernel/printk/printk_ringbuffer.c:2302
 nbcon_seq_force+0x2c/0x60 kernel/printk/nbcon.c:191
 register_console+0x5b1/0x950 kernel/printk/printk.c:4153
 console_store+0x1cc/0x260 drivers/tty/serial/serial_core.c:3035
 dev_attr_store+0x4a/0x70 drivers/base/core.c:2509
 sysfs_kf_write+0xfe/0x120 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x1d2/0x2e0 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x57f/0x9a0 fs/read_write.c:687
 ksys_write+0xdc/0x1a0 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:747
 x64_sys_call+0x154e/0x2550 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000cf925 -> 0x00000000000d1925

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 32372 Comm: syz.5.6728 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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printk: console [ttyS0] enabled