syzbot

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BUG: KCSAN: data-race in __stop_tty / pty_write_room

write to 0xffff88813ec005bc of 1 bytes by task 13824 on cpu 1:
 __stop_tty+0x3e/0x80 drivers/tty/tty_io.c:760
 n_tty_ioctl_helper+0x2bd/0x340 drivers/tty/tty_ioctl.c:872
 n_tty_ioctl+0xfc/0x1f0 drivers/tty/n_tty.c:2381
 tty_ioctl+0x71e/0x970 drivers/tty/tty_io.c:2787
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813ec005bc of 1 bytes by task 225 on cpu 0:
 pty_write_room+0x18/0x80 drivers/tty/pty.c:141
 tty_write_room+0x34/0x50 drivers/tty/tty_ioctl.c:79
 __process_echoes+0x31/0x650 drivers/tty/n_tty.c:616
 flush_echoes drivers/tty/n_tty.c:812 [inline]
 __receive_buf drivers/tty/n_tty.c:1551 [inline]
 n_tty_receive_buf_common+0x4a0b/0x4c40 drivers/tty/n_tty.c:1645
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1680
 tty_ldisc_receive_buf+0x5b/0xf0 drivers/tty/tty_buffer.c:451
 tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:39
 receive_buf drivers/tty/tty_buffer.c:471 [inline]
 flush_to_ldisc+0x1ca/0x2f0 drivers/tty/tty_buffer.c:521
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 225 Comm: kworker/u4:3 Not tainted 5.18.0-rc7-syzkaller-00121-g3d7285a335ed-dirty #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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