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BUG: KCSAN: data-race in n_tty_receive_buf_common / n_tty_write

write to 0xffffc90001a9b020 of 8 bytes by task 25151 on cpu 0:
 process_echoes drivers/tty/n_tty.c:766 [inline]
 n_tty_write+0x1e4/0xb80 drivers/tty/n_tty.c:2352
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x378/0x680 drivers/tty/tty_io.c:1081
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffc90001a9b020 of 8 bytes by task 13004 on cpu 1:
 flush_echoes drivers/tty/n_tty.c:780 [inline]
 __receive_buf drivers/tty/n_tty.c:1618 [inline]
 n_tty_receive_buf_common+0x869/0xc00 drivers/tty/n_tty.c:1715
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
 tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:394
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:452 [inline]
 flush_to_ldisc+0x148/0x340 drivers/tty/tty_buffer.c:502
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
 worker_thread+0x58a/0x780 kernel/workqueue.c:3478
 kthread+0x22a/0x280 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: 0x0000000000000000 -> 0x0000000000000011

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 13004 Comm: kworker/u8:17 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound flush_to_ldisc
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