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BUG: KCSAN: data-race in _prb_read_valid / string

write to 0xffffffff895b50c8 of 1 bytes by task 22458 on cpu 1:
 string_nocheck lib/vsprintf.c:652 [inline]
 string+0x165/0x220 lib/vsprintf.c:730
 vsnprintf+0x543/0x8c0 lib/vsprintf.c:2949
 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
 dev_vprintk_emit+0x242/0x2a0 drivers/base/core.c:5000
 dev_printk_emit+0x84/0xb0 drivers/base/core.c:5011
 __netdev_printk+0x34b/0x370 net/core/dev.c:13146
 netdev_warn+0xa6/0xd0 net/core/dev.c:13199
 ieee802154_subif_start_xmit+0xd7/0x100 net/mac802154/tx.c:232
 __netdev_start_xmit include/linux/netdevice.h:5429 [inline]
 netdev_start_xmit include/linux/netdevice.h:5438 [inline]
 xmit_one net/core/dev.c:3937 [inline]
 dev_hard_start_xmit+0x10c/0x380 net/core/dev.c:3953
 sch_direct_xmit+0x199/0x580 net/sched/sch_generic.c:372
 __dev_xmit_skb net/core/dev.c:4262 [inline]
 __dev_queue_xmit+0xda5/0x1e90 net/core/dev.c:4884
 dev_queue_xmit include/linux/netdevice.h:3461 [inline]
 __bpf_tx_skb net/core/filter.c:2160 [inline]
 __bpf_redirect_common net/core/filter.c:2204 [inline]
 __bpf_redirect+0x83a/0x960 net/core/filter.c:2211
 ____bpf_clone_redirect net/core/filter.c:2501 [inline]
 bpf_clone_redirect+0x206/0x280 net/core/filter.c:2464
 bpf_prog_43388ee67a65acbd+0x22/0x2a
 bpf_dispatcher_nop_func include/linux/bpf.h:1452 [inline]
 __bpf_prog_run include/linux/filter.h:779 [inline]
 bpf_prog_run include/linux/filter.h:786 [inline]
 bpf_test_run+0x29b/0x620 net/bpf/test_run.c:422
 bpf_prog_test_run_skb+0xe67/0x11b0 net/bpf/test_run.c:1225
 bpf_prog_test_run+0x208/0x340 kernel/bpf/syscall.c:4804
 __sys_bpf+0x8da/0xc30 kernel/bpf/syscall.c:6385
 __do_sys_bpf kernel/bpf/syscall.c:6486 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6483 [inline]
 __x64_sys_bpf+0x69/0x80 kernel/bpf/syscall.c:6483
 x64_sys_call+0xf26/0x2550 arch/x86/include/generated/asm/syscalls_64.h:322
 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 0xffffffff895b50c8 of 45 bytes by task 15 on cpu 0:
 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: 0 UID: 0 PID: 15 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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