syzbot

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BUG: KCSAN: data-race in __start_tty / pty_write_room

write to 0xffff8881786c19bc of 1 bytes by task 477 on cpu 0:
 __start_tty+0x73/0x160 drivers/tty/tty_io.c:787
 n_tty_ioctl_helper+0x112/0x240 drivers/tty/tty_ioctl.c:979
 n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2482
 tty_ioctl+0x86f/0xbc0 drivers/tty/tty_io.c:2786
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881786c19bc of 1 bytes by task 4247 on cpu 1:
 pty_write_room+0x1c/0x80 drivers/tty/pty.c:131
 tty_write_room+0x38/0x50 drivers/tty/tty_ioctl.c:81
 __process_echoes+0x31/0x620 drivers/tty/n_tty.c:620
 flush_echoes drivers/tty/n_tty.c:816 [inline]
 __receive_buf drivers/tty/n_tty.c:1614 [inline]
 n_tty_receive_buf_common+0x8ff/0xb50 drivers/tty/n_tty.c:1710
 n_tty_receive_buf2+0x32/0x40 drivers/tty/n_tty.c:1745
 tty_ldisc_receive_buf+0x60/0xe0 drivers/tty/tty_buffer.c:457
 tty_port_default_receive_buf+0x58/0x80 drivers/tty/tty_port.c:39
 receive_buf drivers/tty/tty_buffer.c:515 [inline]
 flush_to_ldisc+0x1ca/0x400 drivers/tty/tty_buffer.c:565
 process_one_work+0x3e6/0x750 kernel/workqueue.c:2405
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2552
 kthread+0x1d7/0x210 kernel/kthread.c:379
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

value changed: 0x01 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4247 Comm: kworker/u4:7 Not tainted 6.4.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/28/2023
Workqueue: events_unbound flush_to_ldisc
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