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BUG: KCSAN: data-race in isig / pty_unix98_ioctl

write to 0xffff8881027c7dd9 of 1 bytes by task 3273 on cpu 0:
 pty_unix98_ioctl+0x2a2/0x2e0 drivers/tty/pty.c:661
 tty_ioctl+0xa8a/0x1130 drivers/tty/tty_io.c:2805
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:860
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881027c7dd9 of 1 bytes by task 510 on cpu 1:
 n_tty_packet_mode_flush drivers/tty/n_tty.c:345 [inline]
 isig+0x1b5/0x280 drivers/tty/n_tty.c:1146
 n_tty_receive_signal_char drivers/tty/n_tty.c:1240 [inline]
 n_tty_receive_char_special drivers/tty/n_tty.c:1281 [inline]
 n_tty_receive_buf_standard drivers/tty/n_tty.c:1558 [inline]
 __receive_buf drivers/tty/n_tty.c:1577 [inline]
 n_tty_receive_buf_common+0x12c5/0x4e70 drivers/tty/n_tty.c:1674
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1709
 tty_ldisc_receive_buf+0x5b/0xf0 drivers/tty/tty_buffer.c:471
 tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:39
 receive_buf drivers/tty/tty_buffer.c:491 [inline]
 flush_to_ldisc+0x1c5/0x2c0 drivers/tty/tty_buffer.c:543
 process_one_work+0x3fc/0x980 kernel/workqueue.c:2297
 worker_thread+0x616/0xa70 kernel/workqueue.c:2444
 kthread+0x2c7/0x2e0 kernel/kthread.c:327
 ret_from_fork+0x1f/0x30

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 510 Comm: kworker/u4:3 Not tainted 5.15.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
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