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BUG: KCSAN: data-race in n_tty_poll / n_tty_set_termios

write to 0xffffc9000dd6b05d of 1 bytes by task 15975 on cpu 0:
 n_tty_set_termios+0x1fd/0x840 drivers/tty/n_tty.c:1782
 tty_set_termios+0x843/0x8a0 drivers/tty/tty_ioctl.c:370
 set_termios+0x241/0x270 drivers/tty/tty_ioctl.c:517
 tty_mode_ioctl+0x3e1/0x580
 n_tty_ioctl_helper+0x8d/0x240 drivers/tty/tty_ioctl.c:980
 n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2483
 tty_ioctl+0x86f/0xbc0 drivers/tty/tty_io.c:2786
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffc9000dd6b05d of 1 bytes by task 15971 on cpu 1:
 input_available_p drivers/tty/n_tty.c:1901 [inline]
 n_tty_poll+0x116/0x490 drivers/tty/n_tty.c:2426
 tty_poll+0x7b/0xf0 drivers/tty/tty_io.c:2207
 vfs_poll include/linux/poll.h:88 [inline]
 ep_item_poll fs/eventpoll.c:855 [inline]
 ep_insert+0x83c/0xba0 fs/eventpoll.c:1524
 do_epoll_ctl+0x618/0x940 fs/eventpoll.c:2165
 __do_sys_epoll_ctl fs/eventpoll.c:2216 [inline]
 __se_sys_epoll_ctl fs/eventpoll.c:2207 [inline]
 __x64_sys_epoll_ctl+0xc6/0xf0 fs/eventpoll.c:2207
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00 -> 0x0c

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15971 Comm: syz-executor.5 Not tainted 6.3.0-rc2-syzkaller-00016-g4979bf866825 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
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