syzbot

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BUG: KCSAN: data-race in __stop_tty / pty_write

write to 0xffff88811a9bd9bc of 1 bytes by task 7693 on cpu 0:
 __stop_tty+0x36/0x90 drivers/tty/tty_io.c:744
 n_tty_ioctl_helper+0x1e9/0x210 drivers/tty/tty_ioctl.c:951
 n_tty_ioctl+0x101/0x200 drivers/tty/n_tty.c:2509
 tty_ioctl+0x845/0xb80 drivers/tty/tty_io.c:2801
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:893
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
 x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a9bd9bc of 1 bytes by task 3783 on cpu 1:
 pty_write+0x24/0x90 drivers/tty/pty.c:115
 tty_put_char+0x8c/0xc0 drivers/tty/tty_io.c:3154
 n_tty_process_echo_ops drivers/tty/n_tty.c:648 [inline]
 __process_echoes+0x309/0x6b0 drivers/tty/n_tty.c:693
 commit_echoes drivers/tty/n_tty.c:756 [inline]
 n_tty_receive_char+0x588/0x6a0 drivers/tty/n_tty.c:1421
 n_tty_receive_buf_standard+0x473/0x2f10 drivers/tty/n_tty.c:1590
 __receive_buf drivers/tty/n_tty.c:1624 [inline]
 n_tty_receive_buf_common+0x805/0xbe0 drivers/tty/n_tty.c:1723
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1769
 tty_ldisc_receive_buf+0x63/0xf0 drivers/tty/tty_buffer.c:387
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x144/0x360 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3321
 worker_thread+0x582/0x770 kernel/workqueue.c:3402
 kthread+0x486/0x510 kernel/kthread.c:464
 ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3783 Comm: kworker/u8:45 Tainted: G        W           6.16.0-rc1-syzkaller-00003-gf09079bd04a9 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events_unbound flush_to_ldisc
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