syzbot

==================================================================
BUG: KCSAN: data-race in n_tty_lookahead_flow_ctrl / tty_set_termios

write to 0xffff888114b19ce0 of 44 bytes by task 17715 on cpu 1:
 tty_set_termios+0xc0/0x900 drivers/tty/tty_ioctl.c:335
 set_termios+0x4a7/0x4f0 drivers/tty/tty_ioctl.c:512
 tty_mode_ioctl+0x37f/0x5b0 drivers/tty/tty_ioctl.c:-1
 n_tty_ioctl_helper+0x87/0x370 drivers/tty/tty_ioctl.c:982
 n_tty_ioctl+0x101/0x200 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+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888114b19cfa of 1 bytes by task 15015 on cpu 0:
 n_tty_is_char_flow_ctrl drivers/tty/n_tty.c:1196 [inline]
 n_tty_receive_char_flow_ctrl drivers/tty/n_tty.c:1217 [inline]
 n_tty_lookahead_flow_ctrl+0x1b0/0x2d0 drivers/tty/n_tty.c:1492
 tty_port_default_lookahead_buf+0x91/0xc0 drivers/tty/tty_port.c:59
 lookahead_bufs drivers/tty/tty_buffer.c:435 [inline]
 flush_to_ldisc+0x279/0x330 drivers/tty/tty_buffer.c:505
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0x4d4/0x9a0 kernel/workqueue.c:3405
 worker_thread+0x569/0x750 kernel/workqueue.c:3486
 kthread+0x221/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x13 -> 0x40

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 15015 Comm: kworker/u8:22 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound flush_to_ldisc
==================================================================