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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86c74af0 of 8 bytes by task 18314 on cpu 0:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 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
 br_set_state+0x2ae/0x3b0 net/bridge/br_stp.c:57
 br_make_forwarding+0xbc/0x150 net/bridge/br_stp.c:455
 br_port_state_selection+0x113/0x330 net/bridge/br_stp.c:-1
 br_stp_enable_port+0xd4/0x110 net/bridge/br_stp_if.c:94
 br_port_carrier_check+0x200/0x230 net/bridge/br_if.c:89
 br_device_event+0x421/0x640 net/bridge/br.c:101
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x83/0x1c0 kernel/notifier.c:453
 call_netdevice_notifiers_info net/core/dev.c:2249 [inline]
 netif_state_change+0x1b8/0x250 net/core/dev.c:1603
 linkwatch_do_dev net/core/link_watch.c:186 [inline]
 __linkwatch_run_queue+0x60b/0x920 net/core/link_watch.c:240
 linkwatch_event+0x40/0x50 net/core/link_watch.c:314
 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 0xffffffff86c74af0 of 16 bytes by task 2988 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x950 kernel/printk/printk_ringbuffer.c:2170
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2988 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
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