syzbot

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BUG: KCSAN: data-race in n_tty_flush_buffer / n_tty_lookahead_flow_ctrl

write to 0xffffc9000e40b270 of 8 bytes by task 30619 on cpu 0:
 reset_buffer_flags drivers/tty/n_tty.c:328 [inline]
 n_tty_flush_buffer+0x9f/0x180 drivers/tty/n_tty.c:359
 tty_ldisc_hangup+0x6e/0x360 drivers/tty/tty_ldisc.c:693
 __tty_hangup+0x3c6/0x530 drivers/tty/tty_io.c:630
 tty_vhangup+0x17/0x20 drivers/tty/tty_io.c:700
 pty_close+0x262/0x280 drivers/tty/pty.c:79
 tty_release+0x204/0x930 drivers/tty/tty_io.c:1756
 __fput+0x299/0x630 fs/file_table.c:394
 ____fput+0x15/0x20 fs/file_table.c:422
 task_work_run+0x135/0x1a0 kernel/task_work.c:180
 get_signal+0xf04/0x10a0 kernel/signal.c:2680
 arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:309
 exit_to_user_mode_loop+0x6f/0xe0 kernel/entry/common.c:168
 exit_to_user_mode_prepare+0x6c/0xb0 kernel/entry/common.c:204
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
 do_syscall_64+0x50/0x110 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read-write to 0xffffc9000e40b270 of 8 bytes by task 5218 on cpu 1:
 n_tty_lookahead_flow_ctrl+0x48/0x130 drivers/tty/n_tty.c:1507
 tty_port_default_lookahead_buf+0x87/0xb0 drivers/tty/tty_port.c:59
 lookahead_bufs drivers/tty/tty_buffer.c:427 [inline]
 flush_to_ldisc+0x30c/0x400 drivers/tty/tty_buffer.c:497
 process_one_work kernel/workqueue.c:2627 [inline]
 process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2700
 worker_thread+0x525/0x730 kernel/workqueue.c:2781
 kthread+0x1d7/0x210 kernel/kthread.c:388
 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

value changed: 0x0000000000001202 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 5218 Comm: kworker/u4:10 Not tainted 6.7.0-rc6-syzkaller-00168-g9a6b294ab496 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Workqueue: events_unbound flush_to_ldisc
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