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BUG: KCSAN: data-race in n_tty_write / tty_set_termios

write to 0xffff8881248d5d1c of 4 bytes by task 8308 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:254 [inline]
 tty_set_termios+0x1c2/0x8a0 drivers/tty/tty_ioctl.c:331
 set_termios+0x341/0x360 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+0xa44/0xfc0 drivers/tty/tty_io.c:2665
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl fs/ioctl.c:753 [inline]
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl+0xc9/0x130 fs/ioctl.c:760
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:760
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881248d5d1c of 4 bytes by task 15599 on cpu 1:
 n_tty_write+0x86/0xac0 drivers/tty/n_tty.c:2310
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x3e8/0x5c0 drivers/tty/tty_io.c:1046
 __vfs_write+0x69/0x340 fs/read_write.c:495
 vfs_write+0x19b/0x350 fs/read_write.c:559
 ksys_write+0xce/0x180 fs/read_write.c:612
 __do_sys_write fs/read_write.c:624 [inline]
 __se_sys_write fs/read_write.c:621 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:621
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15599 Comm: syz-executor.2 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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