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BUG: KCSAN: data-race in n_tty_write / tty_set_termios

write to 0xffff88813d6e8914 of 4 bytes by task 17846 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:233 [inline]
 tty_set_termios+0x1c2/0x8a0 drivers/tty/tty_ioctl.c:355
 set_termios+0x375/0x3b0 drivers/tty/tty_ioctl.c:438
 tty_mode_ioctl+0x573/0x670 drivers/tty/tty_ioctl.c:749
 n_tty_ioctl_helper+0x89/0x4c0 drivers/tty/tty_ioctl.c:907
 n_tty_ioctl+0x102/0x200 drivers/tty/n_tty.c:2421
 tty_ioctl+0xa8f/0x1120 drivers/tty/tty_io.c:2814
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813d6e8914 of 4 bytes by task 17869 on cpu 1:
 n_tty_write+0x86/0xaf0 drivers/tty/n_tty.c:2265
 do_tty_write drivers/tty/tty_io.c:1038 [inline]
 file_tty_write+0x409/0x660 drivers/tty/tty_io.c:1110
 tty_write+0x24/0x30 drivers/tty/tty_io.c:1131
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00008a3b -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17869 Comm: syz-executor.3 Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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