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BUG: KCSAN: data-race in n_tty_receive_char_special / n_tty_receive_char_special

write to 0xffffc9000e54d018 of 8 bytes by task 31001 on cpu 1:
 echo_char_raw drivers/tty/n_tty.c:841 [inline]
 eraser drivers/tty/n_tty.c:1076 [inline]
 n_tty_receive_char_special+0x1797/0x3ac0 drivers/tty/n_tty.c:1313
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1607 [inline]
 __receive_buf drivers/tty/n_tty.c:1641 [inline]
 n_tty_receive_buf_common+0xe0c/0x1e20 drivers/tty/n_tty.c:1740
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1769
 tiocsti drivers/tty/tty_io.c:2315 [inline]
 tty_ioctl+0x968/0x1120 drivers/tty/tty_io.c:2721
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffc9000e54d018 of 8 bytes by task 30989 on cpu 0:
 echo_char_raw drivers/tty/n_tty.c:841 [inline]
 eraser drivers/tty/n_tty.c:1077 [inline]
 n_tty_receive_char_special+0x17bf/0x3ac0 drivers/tty/n_tty.c:1313
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1607 [inline]
 __receive_buf drivers/tty/n_tty.c:1641 [inline]
 n_tty_receive_buf_common+0xe0c/0x1e20 drivers/tty/n_tty.c:1740
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1769
 tiocsti drivers/tty/tty_io.c:2315 [inline]
 tty_ioctl+0x968/0x1120 drivers/tty/tty_io.c:2721
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30989 Comm: syz-executor.4 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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