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BUG: KCSAN: data-race in __tty_hangup / n_tty_poll

write to 0xffff888121df55e4 of 2 bytes by task 2112 on cpu 1:
 __tty_hangup+0x4e9/0x610 drivers/tty/tty_io.c:634
 tty_vhangup drivers/tty/tty_io.c:698 [inline]
 tty_ioctl+0x5a1/0xfd0 drivers/tty/tty_io.c:2597
 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 0xffff888121df55e4 of 2 bytes by task 2104 on cpu 0:
 n_tty_poll+0x3aa/0x4a0 drivers/tty/n_tty.c:2416
 tty_poll+0xa7/0x140 drivers/tty/tty_io.c:2112
 vfs_poll include/linux/poll.h:90 [inline]
 do_pollfd fs/select.c:869 [inline]
 do_poll fs/select.c:917 [inline]
 do_sys_poll+0x606/0xbc0 fs/select.c:1011
 __do_sys_ppoll fs/select.c:1111 [inline]
 __se_sys_ppoll+0x169/0x1b0 fs/select.c:1091
 __x64_sys_ppoll+0x63/0x70 fs/select.c:1091
 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: 0 PID: 2104 Comm: syz-executor.5 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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