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BUG: KCSAN: data-race in _prb_read_valid / vsnprintf

write to 0xffffffff895cd7d0 of 39 bytes by interrupt on cpu 0:
 vsnprintf+0x2c0/0x8c0 lib/vsprintf.c:2900
 vscnprintf+0x41/0x90 lib/vsprintf.c:3018
 printk_sprint+0x30/0x2b0 kernel/printk/printk.c:2222
 vprintk_store+0x57f/0x910 kernel/printk/printk.c:2364
 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
 lapbeth_xmit+0x1bd/0x1c0 drivers/net/wan/lapbether.c:-1
 __netdev_start_xmit include/linux/netdevice.h:5432 [inline]
 netdev_start_xmit include/linux/netdevice.h:5441 [inline]
 xmit_one net/core/dev.c:3953 [inline]
 dev_hard_start_xmit+0x10c/0x380 net/core/dev.c:3969
 __dev_queue_xmit+0xbfd/0x1ec0 net/core/dev.c:4958
 dev_queue_xmit include/linux/netdevice.h:3464 [inline]
 x25_send_frame+0xfe/0x130 net/x25/x25_dev.c:193
 x25_transmit_restart_request net/x25/x25_link.c:153 [inline]
 x25_link_control+0x2a9/0x500 net/x25/x25_link.c:102
 x25_receive_data net/x25/x25_dev.c:43 [inline]
 x25_lapb_receive_frame+0x2d6/0x770 net/x25/x25_dev.c:127
 __netif_receive_skb_one_core net/core/dev.c:6297 [inline]
 netif_receive_skb_core+0x122/0x130 net/core/dev.c:6322
 lapbeth_napi_poll+0x42/0x90 drivers/net/wan/lapbether.c:100
 __napi_poll+0x61/0x300 net/core/dev.c:7830
 napi_poll net/core/dev.c:7893 [inline]
 net_rx_action+0x456/0x930 net/core/dev.c:8050
 handle_softirqs+0xcc/0x2a0 kernel/softirq.c:645
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1099
 smpboot_thread_fn+0x32f/0x520 kernel/smpboot.c:160
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff895cd7d8 of 28 bytes by task 15 on cpu 1:
 copy_data kernel/printk/printk_ringbuffer.c:1911 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1996 [inline]
 _prb_read_valid+0x882/0x930 kernel/printk/printk_ringbuffer.c:2173
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 printk_get_next_message+0xea/0x550 kernel/printk/printk.c:3052
 nbcon_emit_next_record+0x4af/0x1bc0 kernel/printk/nbcon.c:1017
 nbcon_emit_one kernel/printk/nbcon.c:1157 [inline]
 nbcon_kthread_func+0x3fd/0x690 kernel/printk/nbcon.c:1271
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 15 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
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