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BUG: KCSAN: data-race in do_con_write / n_tty_ioctl_helper

write to 0xffff88814e7ca1cc of 1 bytes by task 13868 on cpu 1:
 n_tty_ioctl_helper+0x106/0x4c0 drivers/tty/tty_ioctl.c:851
 n_tty_ioctl+0x102/0x200 drivers/tty/n_tty.c:2486
 tty_ioctl+0xa9b/0x1130 drivers/tty/tty_io.c:2810
 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+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814e7ca1cc of 1 bytes by task 13871 on cpu 0:
 do_con_write+0x1fb5/0x5d90 drivers/tty/vt/vt.c:2890
 con_write+0x20/0x40 drivers/tty/vt/vt.c:3254
 n_tty_write+0x39b/0xaf0 drivers/tty/n_tty.c:2376
 do_tty_write drivers/tty/tty_io.c:1043 [inline]
 file_tty_write+0x409/0x660 drivers/tty/tty_io.c:1133
 tty_write+0x24/0x30 drivers/tty/tty_io.c:1140
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13871 Comm: syz-executor.4 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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