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BUG: KCSAN: data-race in n_tty_write / tty_set_termios

read-write to 0xffff8881078f911c of 4 bytes by task 8152 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:254 [inline]
 tty_set_termios+0x1a3/0x870 drivers/tty/tty_ioctl.c:331
 set_termios+0x375/0x3b0 drivers/tty/tty_ioctl.c:414
 tty_mode_ioctl+0x57c/0x680 drivers/tty/tty_ioctl.c:725
 n_tty_ioctl_helper+0x8b/0x460 drivers/tty/tty_ioctl.c:883
 n_tty_ioctl+0x102/0x200 drivers/tty/n_tty.c:2465
 tty_ioctl+0xa9f/0x1030 drivers/tty/tty_io.c:2670
 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 0xffff8881078f911c of 4 bytes by task 18977 on cpu 1:
 n_tty_write+0x86/0xae0 drivers/tty/n_tty.c:2309
 do_tty_write drivers/tty/tty_io.c:961 [inline]
 tty_write+0x3e9/0x630 drivers/tty/tty_io.c:1049
 call_write_iter include/linux/fs.h:1901 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_writev fs/read_write.c:939 [inline]
 do_writev+0x201/0x460 fs/read_write.c:982
 __do_sys_writev fs/read_write.c:1055 [inline]
 __se_sys_writev fs/read_write.c:1052 [inline]
 __x64_sys_writev+0x41/0x50 fs/read_write.c:1052
 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: 18977 Comm: syz-executor.3 Not tainted 5.11.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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