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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86c6eec0 of 8 bytes by interrupt on cpu 1:
 data_alloc+0x2fc/0x380 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8e3/0xaf0 kernel/printk/printk_ringbuffer.c:1727
 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:5387 [inline]
 netdev_start_xmit include/linux/netdevice.h:5396 [inline]
 xmit_one net/core/dev.c:3889 [inline]
 dev_hard_start_xmit+0x10c/0x380 net/core/dev.c:3905
 __dev_queue_xmit+0xb97/0x1e60 net/core/dev.c:4872
 dev_queue_xmit include/linux/netdevice.h:3436 [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+0x2d6/0x770 net/x25/x25_dev.c:127
 __netif_receive_skb_one_core net/core/dev.c:6206 [inline]
 netif_receive_skb_core+0x122/0x130 net/core/dev.c:6231
 lapbeth_napi_poll+0x42/0x90 drivers/net/wan/lapbether.c:100
 __napi_poll+0x61/0x300 net/core/dev.c:7729
 napi_poll net/core/dev.c:7792 [inline]
 net_rx_action+0x456/0x930 net/core/dev.c:7949
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1076
 smpboot_thread_fn+0x32a/0x510 kernel/smpboot.c:160
 kthread+0x221/0x270 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 0xffffffff86c6eec0 of 16 bytes by task 2968 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1934 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1982 [inline]
 _prb_read_valid+0x183/0x930 kernel/printk/printk_ringbuffer.c:2173
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 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+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2968 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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