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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86e9d608 of 88 bytes by task 3440 on cpu 0:
 prb_reserve+0x6fb/0xaf0 kernel/printk/printk_ringbuffer.c:1693
 vprintk_store+0x54e/0x910 kernel/printk/printk.c:2354
 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
 br_set_state+0x2b9/0x390 net/bridge/br_stp.c:57
 br_init_port net/bridge/br_stp_if.c:39 [inline]
 br_stp_enable_port+0x5e/0x110 net/bridge/br_stp_if.c:93
 br_port_carrier_check+0x200/0x230 net/bridge/br_if.c:90
 br_device_event+0x421/0x680 net/bridge/br.c:101
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x72/0x1a0 kernel/notifier.c:453
 call_netdevice_notifiers_info net/core/dev.c:2275 [inline]
 netif_state_change+0x1b8/0x250 net/core/dev.c:1625
 linkwatch_do_dev net/core/link_watch.c:186 [inline]
 __linkwatch_run_queue+0x60d/0x930 net/core/link_watch.c:240
 linkwatch_event+0x40/0x50 net/core/link_watch.c:314
 process_one_work kernel/workqueue.c:3396 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3479
 worker_thread+0x569/0x750 kernel/workqueue.c:3560
 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 0xffffffff86e9d608 of 8 bytes by task 15 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1934 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1982 [inline]
 _prb_read_valid+0x18c/0x930 kernel/printk/printk_ringbuffer.c:2173
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 nbcon_kthread_should_wakeup kernel/printk/nbcon.c:1207 [inline]
 nbcon_kthread_func+0x1ff/0x690 kernel/printk/nbcon.c:1244
 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

value changed: 0x00000000000021a3 -> 0x00000000000041a3

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 07/24/2026
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