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BUG: KCSAN: data-race in echo_char / n_tty_receive_buf_common

write to 0xffffc90001cbd018 of 8 bytes by task 19033 on cpu 1:
 add_echo_byte drivers/tty/n_tty.c:845 [inline]
 echo_char+0x14e/0x1c0 drivers/tty/n_tty.c:948
 eraser drivers/tty/n_tty.c:1043 [inline]
 n_tty_receive_char_special+0x15ad/0x1c10 drivers/tty/n_tty.c:1316
 n_tty_receive_buf_standard drivers/tty/n_tty.c:1584 [inline]
 __receive_buf drivers/tty/n_tty.c:1646 [inline]
 n_tty_receive_buf_common+0x7ef/0x1b00 drivers/tty/n_tty.c:1742
 n_tty_receive_buf+0x3a/0x50 drivers/tty/n_tty.c:1771
 tiocsti drivers/tty/tty_io.c:2200 [inline]
 tty_ioctl+0xb75/0xe10 drivers/tty/tty_io.c:2576
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x84f/0xcf0 fs/ioctl.c:732
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:754
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffc90001cbd018 of 8 bytes by task 18383 on cpu 0:
 add_echo_byte drivers/tty/n_tty.c:843 [inline]
 echo_char_raw drivers/tty/n_tty.c:923 [inline]
 finish_erasing drivers/tty/n_tty.c:961 [inline]
 finish_erasing drivers/tty/n_tty.c:958 [inline]
 n_tty_receive_char_inline drivers/tty/n_tty.c:1416 [inline]
 n_tty_receive_buf_standard drivers/tty/n_tty.c:1583 [inline]
 __receive_buf drivers/tty/n_tty.c:1646 [inline]
 n_tty_receive_buf_common+0x4c2/0x1b00 drivers/tty/n_tty.c:1742
 n_tty_receive_buf2+0x3d/0x60 drivers/tty/n_tty.c:1777
 tty_ldisc_receive_buf+0x71/0xf0 drivers/tty/tty_buffer.c:461
 tty_port_default_receive_buf+0x87/0xd0 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:481 [inline]
 flush_to_ldisc+0x1d5/0x260 drivers/tty/tty_buffer.c:533
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18383 Comm: kworker/u4:10 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
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