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BUG: KCSAN: data-race in n_tty_poll / tty_set_termios

write to 0xffff88812bd5191c of 4 bytes by task 12127 on cpu 1:
 unset_locked_termios drivers/tty/tty_ioctl.c:254 [inline]
 tty_set_termios+0x1c2/0x8a0 drivers/tty/tty_ioctl.c:331
 set_termios+0x375/0x3b0 drivers/tty/tty_ioctl.c:414
 tty_mode_ioctl+0x573/0x670 drivers/tty/tty_ioctl.c:725
 n_tty_ioctl_helper+0x8b/0x4c0 drivers/tty/tty_ioctl.c:883
 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 0xffff88812bd5191c of 4 bytes by task 12114 on cpu 0:
 input_available_p drivers/tty/n_tty.c:1935 [inline]
 n_tty_poll+0x144/0x4a0 drivers/tty/n_tty.c:2429
 tty_poll+0xa7/0x140 drivers/tty/tty_io.c:2232
 vfs_poll include/linux/poll.h:90 [inline]
 ep_item_poll fs/eventpoll.c:840 [inline]
 ep_insert fs/eventpoll.c:1507 [inline]
 do_epoll_ctl+0x100e/0x1860 fs/eventpoll.c:2127
 __do_sys_epoll_ctl fs/eventpoll.c:2178 [inline]
 __se_sys_epoll_ctl fs/eventpoll.c:2169 [inline]
 __x64_sys_epoll_ctl+0xb3/0xe0 fs/eventpoll.c:2169
 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: 12114 Comm: syz-executor.3 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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