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BUG: KCSAN: data-race in __tty_hangup / n_tty_poll

read to 0xffff8880a25369e4 of 1 bytes by task 558 on cpu 1:
 n_tty_poll+0x20f/0x4e0 drivers/tty/n_tty.c:2416
 tty_poll+0xcb/0xf0 drivers/tty/tty_io.c:2112
 vfs_poll include/linux/poll.h:90 [inline]
 do_pollfd fs/select.c:859 [inline]
 do_poll fs/select.c:907 [inline]
 do_sys_poll+0x4ac/0x990 fs/select.c:1001
 __do_sys_ppoll fs/select.c:1101 [inline]
 __se_sys_ppoll fs/select.c:1081 [inline]
 __x64_sys_ppoll+0x156/0x190 fs/select.c:1081
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880a25369e4 of 11 bytes by task 565 on cpu 0:
 __tty_hangup+0x357/0x440 drivers/tty/tty_io.c:634
 tty_vhangup drivers/tty/tty_io.c:698 [inline]
 tty_ioctl+0x395/0xd80 drivers/tty/tty_io.c:2597
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x101/0x150 fs/ioctl.c:763
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x47/0x60 fs/ioctl.c:770
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 565 Comm: syz-executor.3 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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