syzbot

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BUG: KCSAN: data-race in n_tty_lookahead_flow_ctrl / tty_set_termios

read-write to 0xffff88810ea80508 of 4 bytes by task 15253 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:214 [inline]
 tty_set_termios+0xfa/0x8b0 drivers/tty/tty_ioctl.c:340
 set_termios+0x365/0x4e0 drivers/tty/tty_ioctl.c:520
 tty_mode_ioctl+0x391/0x5d0
 n_tty_ioctl_helper+0x8d/0x240 drivers/tty/tty_ioctl.c:986
 n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2511
 tty_ioctl+0x886/0xbe0 drivers/tty/tty_io.c:2812
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:904 [inline]
 __se_sys_ioctl+0xd3/0x150 fs/ioctl.c:890
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:890
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x72/0x7a

read to 0xffff88810ea80508 of 4 bytes by task 3591 on cpu 1:
 n_tty_lookahead_flow_ctrl+0x5b/0x130 drivers/tty/n_tty.c:1509
 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+0x31c/0x410 drivers/tty/tty_buffer.c:498
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0x465/0x990 kernel/workqueue.c:3335
 worker_thread+0x526/0x730 kernel/workqueue.c:3416
 kthread+0x1d1/0x210 kernel/kthread.c:388
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

value changed: 0x00000401 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3591 Comm: kworker/u8:8 Tainted: G        W          6.9.0-rc2-syzkaller-00080-gc85af715cac0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound flush_to_ldisc
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