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BUG: KCSAN: data-race in ppp_asynctty_receive / tty_set_termios

read-write to 0xffff888137b55908 of 4 bytes by task 19983 on cpu 0:
 unset_locked_termios drivers/tty/tty_ioctl.c:214 [inline]
 tty_set_termios+0xfa/0x8a0 drivers/tty/tty_ioctl.c:340
 set_termios+0x47e/0x4c0 drivers/tty/tty_ioctl.c:516
 tty_mode_ioctl+0x391/0x5d0
 ppp_asynctty_ioctl+0x21d/0x2e0 drivers/net/ppp/ppp_async.c:324
 tty_ioctl+0x875/0xbc0 drivers/tty/tty_io.c:2812
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xcf/0x140 fs/ioctl.c:857
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888137b55908 of 4 bytes by task 53 on cpu 1:
 ppp_async_input drivers/net/ppp/ppp_async.c:905 [inline]
 ppp_asynctty_receive+0x751/0x1040 drivers/net/ppp/ppp_async.c:342
 tty_ldisc_receive_buf+0xcc/0xe0 drivers/tty/tty_buffer.c:390
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:444 [inline]
 flush_to_ldisc+0x1ca/0x400 drivers/tty/tty_buffer.c:494
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x5b8/0xa40 kernel/workqueue.c:2706
 worker_thread+0x525/0x730 kernel/workqueue.c:2787
 kthread+0x1d7/0x210 kernel/kthread.c:388
 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

value changed: 0x00000500 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 53 Comm: kworker/u4:4 Not tainted 6.8.0-rc5-syzkaller-00029-g39133352cbed #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Workqueue: events_unbound flush_to_ldisc
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