syzbot

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BUG: KCSAN: data-race in n_tty_receive_char_flow_ctrl / tty_set_termios

write to 0xffff888118be2521 of 1 bytes by task 5441 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:220 [inline]
 tty_set_termios+0x482/0x8b0 drivers/tty/tty_ioctl.c:340
 set_termios+0x4af/0x4f0 drivers/tty/tty_ioctl.c:516
 tty_mode_ioctl+0x396/0x5d0 drivers/tty/tty_ioctl.c:-1
 n_tty_ioctl_helper+0x8d/0x240 drivers/tty/tty_ioctl.c:986
 n_tty_ioctl+0xfd/0x210 drivers/tty/n_tty.c:2521
 tty_ioctl+0x87a/0xbe0 drivers/tty/tty_io.c:2811
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x168d/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888118be2521 of 1 bytes by task 38 on cpu 1:
 n_tty_is_char_flow_ctrl drivers/tty/n_tty.c:1220 [inline]
 n_tty_receive_char_flow_ctrl+0x22/0x1a0 drivers/tty/n_tty.c:1241
 n_tty_lookahead_flow_ctrl+0xee/0x130 drivers/tty/n_tty.c:1516
 tty_port_default_lookahead_buf+0x8a/0xc0 drivers/tty/tty_port.c:59
 lookahead_bufs drivers/tty/tty_buffer.c:428 [inline]
 flush_to_ldisc+0x322/0x410 drivers/tty/tty_buffer.c:498
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4de/0xa20 kernel/workqueue.c:3319
 worker_thread+0x51d/0x6f0 kernel/workqueue.c:3400
 kthread+0x4ae/0x520 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x11 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 38 Comm: kworker/u8:2 Not tainted 6.14.0-syzkaller-05877-g1a9239bb4253 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: events_unbound flush_to_ldisc
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