syzbot

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BUG: KCSAN: data-race in pty_write / tty_send_xchar

write to 0xffff88814c0055bc of 1 bytes by task 11160 on cpu 0:
 __stop_tty drivers/tty/tty_io.c:744 [inline]
 stop_tty drivers/tty/tty_io.c:766 [inline]
 tty_send_xchar+0x1c8/0x2b0 drivers/tty/tty_io.c:1156
 n_tty_ioctl_helper+0x2a9/0x370 drivers/tty/tty_ioctl.c:-1
 n_tty_ioctl+0x101/0x230 drivers/tty/n_tty.c:2496
 tty_ioctl+0x83e/0xb80 drivers/tty/tty_io.c:2801
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88814c0055bc of 1 bytes by task 58 on cpu 1:
 pty_write+0x24/0x90 drivers/tty/pty.c:113
 tty_put_char+0x8f/0xc0 drivers/tty/tty_io.c:3154
 n_tty_process_echo_ops drivers/tty/n_tty.c:643 [inline]
 __process_echoes+0x2f9/0x6b0 drivers/tty/n_tty.c:689
 flush_echoes drivers/tty/n_tty.c:785 [inline]
 __receive_buf drivers/tty/n_tty.c:1618 [inline]
 n_tty_receive_buf_common+0x918/0xc10 drivers/tty/n_tty.c:1715
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
 tty_ldisc_receive_buf+0x66/0xf0 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+0x148/0x340 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x6bc/0x8b0 kernel/workqueue.c:3421
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 58 Comm: kworker/u8:4 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_unbound flush_to_ldisc
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