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BUG: KCSAN: data-race in n_tty_flush_buffer / n_tty_lookahead_flow_ctrl

write to 0xffffc9000166b270 of 8 bytes by task 30109 on cpu 1:
 reset_buffer_flags drivers/tty/n_tty.c:339 [inline]
 n_tty_flush_buffer+0x9f/0x180 drivers/tty/n_tty.c:370
 tty_ldisc_hangup+0x6e/0x360 drivers/tty/tty_ldisc.c:693
 __tty_hangup+0x3ba/0x510 drivers/tty/tty_io.c:631
 tty_vhangup drivers/tty/tty_io.c:701 [inline]
 tty_ioctl+0x604/0xbc0 drivers/tty/tty_io.c:2717
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read-write to 0xffffc9000166b270 of 8 bytes by task 8900 on cpu 0:
 n_tty_lookahead_flow_ctrl+0x46/0x120 drivers/tty/n_tty.c:1489
 tty_port_default_lookahead_buf+0x85/0xb0 drivers/tty/tty_port.c:61
 lookahead_bufs drivers/tty/tty_buffer.c:498 [inline]
 flush_to_ldisc+0x30a/0x400 drivers/tty/tty_buffer.c:568
 process_one_work+0x3e6/0x750 kernel/workqueue.c:2405
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2552
 kthread+0x1d7/0x210 kernel/kthread.c:379
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

value changed: 0x0000000000003a47 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8900 Comm: kworker/u4:12 Not tainted 6.4.0-rc6-syzkaller-00242-g1639fae5132b #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Workqueue: events_unbound flush_to_ldisc
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