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BUG: KCSAN: data-race in ppp_asynctty_receive / tty_set_termios

write to 0xffff88811742c521 of 1 bytes by task 4383 on cpu 1:
 unset_locked_termios drivers/tty/tty_ioctl.c:220 [inline]
 tty_set_termios+0x480/0x8b0 drivers/tty/tty_ioctl.c:340
 set_termios+0x497/0x4e0 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+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
 x64_sys_call+0x155d/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:17
 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+0x77/0x7f

read to 0xffff88811742c521 of 1 bytes by task 1486 on cpu 0:
 ppp_async_input drivers/net/ppp/ppp_async.c:906 [inline]
 ppp_asynctty_receive+0x785/0x1050 drivers/net/ppp/ppp_async.c:342
 tty_ldisc_receive_buf+0xd9/0x100 drivers/tty/tty_buffer.c:391
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x1ce/0x410 drivers/tty/tty_buffer.c:495
 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:244

value changed: 0x11 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1486 Comm: kworker/u8:5 Not tainted 6.9.0-rc3-syzkaller-00355-g7efd0a74039f #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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