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

write to 0xffffffff86cdfa00 of 88 bytes by interrupt on cpu 1:
 prb_reserve+0x6e6/0xae0 kernel/printk/printk_ringbuffer.c:1690
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 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
 lapbeth_xmit+0x1bd/0x1c0 drivers/net/wan/lapbether.c:-1
 __netdev_start_xmit include/linux/netdevice.h:5275 [inline]
 netdev_start_xmit include/linux/netdevice.h:5284 [inline]
 xmit_one net/core/dev.c:3871 [inline]
 dev_hard_start_xmit+0x136/0x3f0 net/core/dev.c:3887
 __dev_queue_xmit+0xd9c/0x1f40 net/core/dev.c:4836
 dev_queue_xmit include/linux/netdevice.h:3384 [inline]
 x25_send_frame+0xfe/0x130 net/x25/x25_dev.c:193
 x25_transmit_restart_confirmation net/x25/x25_link.c:178 [inline]
 x25_link_control+0x3d1/0x500 net/x25/x25_link.c:-1
 x25_receive_data net/x25/x25_dev.c:43 [inline]
 x25_lapb_receive_frame+0x2e0/0x770 net/x25/x25_dev.c:127
 __netif_receive_skb_one_core net/core/dev.c:6156 [inline]
 netif_receive_skb_core+0x122/0x130 net/core/dev.c:6181
 lapbeth_napi_poll+0x42/0x90 drivers/net/wan/lapbether.c:100
 __napi_poll+0x61/0x330 net/core/dev.c:7685
 napi_poll net/core/dev.c:7748 [inline]
 net_rx_action+0x452/0x930 net/core/dev.c:7900
 handle_softirqs+0xb9/0x2a0 kernel/softirq.c:622
 do_softirq+0x45/0x60 kernel/softirq.c:523
 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 netif_rx+0x83/0x220 net/core/dev.c:5722
 macvlan_broadcast+0x268/0x3a0 drivers/net/macvlan.c:292
 macvlan_multicast_rx drivers/net/macvlan.c:304 [inline]
 macvlan_process_broadcast+0x28b/0x320 drivers/net/macvlan.c:340
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0x4de/0x9e0 kernel/workqueue.c:3358
 worker_thread+0x581/0x770 kernel/workqueue.c:3439
 kthread+0x22a/0x280 kernel/kthread.c:467
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff86cdfa00 of 8 bytes by task 2991 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:2014 [inline]
 _prb_read_valid+0x383/0x950 kernel/printk/printk_ringbuffer.c:2171
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 syslog_print+0x258/0x560 kernel/printk/printk.c:1628
 do_syslog+0x52b/0x7f0 kernel/printk/printk.c:1763
 __do_sys_syslog kernel/printk/printk.c:1855 [inline]
 __se_sys_syslog kernel/printk/printk.c:1853 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1853
 x64_sys_call+0x2b9e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000002ca0 -> 0x0000000000004ca0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2991 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================