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BUG: KCSAN: data-race in ppp_asynctty_receive / tty_set_termios

read-write to 0xffff88813a0f9108 of 4 bytes by task 9355 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:230 [inline]
 tty_set_termios+0xf9/0x890 drivers/tty/tty_ioctl.c:355
 set_termios+0x388/0x3c0 drivers/tty/tty_ioctl.c:438
 tty_mode_ioctl+0x4fa/0x5d0
 n_tty_ioctl_helper+0x83/0x340 drivers/tty/tty_ioctl.c:901
 n_tty_ioctl+0xfc/0x1f0 drivers/tty/n_tty.c:2430
 tty_ioctl+0x71e/0x970 drivers/tty/tty_io.c:2787
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

read to 0xffff88813a0f9108 of 4 bytes by task 13991 on cpu 1:
 ppp_async_input drivers/net/ppp/ppp_async.c:910 [inline]
 ppp_asynctty_receive+0x7d4/0xdb0 drivers/net/ppp/ppp_async.c:349
 tty_ldisc_receive_buf+0xc0/0xf0 drivers/tty/tty_buffer.c:456
 tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:39
 receive_buf drivers/tty/tty_buffer.c:472 [inline]
 flush_to_ldisc+0x1ca/0x2f0 drivers/tty/tty_buffer.c:522
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x00000500 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13991 Comm: kworker/u4:56 Not tainted 5.19.0-rc1-syzkaller-00303-g7a68065eb9cd-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
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