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BUG: KCSAN: data-race in n_tty_poll / n_tty_set_termios

write to 0xffffc9000b22505d of 1 bytes by task 30915 on cpu 0:
 n_tty_set_termios+0x211/0x800 drivers/tty/n_tty.c:1815
 tty_set_termios+0x846/0x8a0 drivers/tty/tty_ioctl.c:341
 set_termios+0x343/0x370 drivers/tty/tty_ioctl.c:414
 tty_mode_ioctl+0x636/0x7c0 drivers/tty/tty_ioctl.c:770
 n_tty_ioctl_helper+0x8b/0x460 drivers/tty/tty_ioctl.c:940
 n_tty_ioctl+0x102/0x200 drivers/tty/n_tty.c:2466
 tty_ioctl+0xa5a/0xfd0 drivers/tty/tty_io.c:2665
 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 0xffffc9000b22505d of 1 bytes by task 14201 on cpu 1:
 input_available_p drivers/tty/n_tty.c:1936 [inline]
 n_tty_poll+0x112/0x4a0 drivers/tty/n_tty.c:2409
 tty_poll+0xa7/0x140 drivers/tty/tty_io.c:2112
 vfs_poll include/linux/poll.h:90 [inline]
 do_select+0x8f6/0xf70 fs/select.c:534
 core_sys_select+0x3e3/0x610 fs/select.c:677
 kern_select fs/select.c:718 [inline]
 __do_sys_select fs/select.c:725 [inline]
 __se_sys_select+0x17e/0x1c0 fs/select.c:722
 __x64_sys_select+0x63/0x70 fs/select.c:722
 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: 1 PID: 14201 Comm: agetty Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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