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BUG: KCSAN: data-race in n_tty_receive_char_special / n_tty_receive_char_special

write to 0xffffc900073d7018 of 8 bytes by task 15079 on cpu 0:
 echo_char_raw drivers/tty/n_tty.c:844 [inline]
 eraser drivers/tty/n_tty.c:1079 [inline]
 n_tty_receive_char_special+0x1736/0x3a70 drivers/tty/n_tty.c:1316
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1610 [inline]
 __receive_buf drivers/tty/n_tty.c:1644 [inline]
 n_tty_receive_buf_common+0xe48/0x1e70 drivers/tty/n_tty.c:1742
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1771
 tiocsti drivers/tty/tty_io.c:2196 [inline]
 tty_ioctl+0x8e3/0xfd0 drivers/tty/tty_io.c:2572
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffc900073d7018 of 8 bytes by task 15069 on cpu 1:
 echo_char_raw drivers/tty/n_tty.c:1090 [inline]
 eraser drivers/tty/n_tty.c:1079 [inline]
 n_tty_receive_char_special+0x16ff/0x3a70 drivers/tty/n_tty.c:1316
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1610 [inline]
 __receive_buf drivers/tty/n_tty.c:1644 [inline]
 n_tty_receive_buf_common+0xe48/0x1e70 drivers/tty/n_tty.c:1742
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1771
 tiocsti drivers/tty/tty_io.c:2196 [inline]
 tty_ioctl+0x8e3/0xfd0 drivers/tty/tty_io.c:2572
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15069 Comm: syz-executor.3 Not tainted 5.9.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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