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BUG: KCSAN: data-race in n_tty_lookahead_flow_ctrl / tty_set_termios

write to 0xffff8881708fd921 of 1 bytes by task 19704 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:236 [inline]
 tty_set_termios+0x48a/0x8a0 drivers/tty/tty_ioctl.c:357
 set_termios+0x388/0x3c0 drivers/tty/tty_ioctl.c:442
 tty_mode_ioctl+0x4fa/0x5d0
 n_tty_ioctl_helper+0x83/0x340 drivers/tty/tty_ioctl.c:905
 n_tty_ioctl+0xfc/0x1f0 drivers/tty/n_tty.c:2483
 tty_ioctl+0x71e/0x970 drivers/tty/tty_io.c:2787
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881708fd921 of 1 bytes by task 1845 on cpu 1:
 n_tty_is_char_flow_ctrl drivers/tty/n_tty.c:1230 [inline]
 n_tty_receive_char_flow_ctrl drivers/tty/n_tty.c:1251 [inline]
 n_tty_lookahead_flow_ctrl+0x12a/0x2f0 drivers/tty/n_tty.c:1499
 tty_port_default_lookahead_buf+0x81/0xb0 drivers/tty/tty_port.c:61
 lookahead_bufs drivers/tty/tty_buffer.c:496 [inline]
 flush_to_ldisc+0x346/0x480 drivers/tty/tty_buffer.c:564
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x11 -> 0x48

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1845 Comm: kworker/u4:4 Tainted: G        W          6.0.0-rc1-syzkaller-00368-gf31c32efd57c-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Workqueue: events_unbound flush_to_ldisc
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