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BUG: KCSAN: data-race in ppp_asynctty_receive / tty_set_termios

write to 0xffff88811e4d20e0 of 44 bytes by task 7760 on cpu 0:
 tty_set_termios+0xc0/0x900 drivers/tty/tty_ioctl.c:335
 set_termios+0x4a7/0x4f0 drivers/tty/tty_ioctl.c:512
 tty_mode_ioctl+0x37f/0x5b0 drivers/tty/tty_ioctl.c:-1
 ppp_asynctty_ioctl+0xcb/0x1e0 drivers/net/ppp/ppp_async.c:258
 tty_ioctl+0x83e/0xb80 drivers/tty/tty_io.c:2774
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x239d/0x2550 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811e4d20e0 of 4 bytes by task 12 on cpu 1:
 ppp_async_input drivers/net/ppp/ppp_async.c:835 [inline]
 ppp_asynctty_receive+0x676/0xc60 drivers/net/ppp/ppp_async.c:275
 tty_ldisc_receive_buf+0xbf/0xf0 drivers/tty/tty_buffer.c:398
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:452 [inline]
 flush_to_ldisc+0x13a/0x330 drivers/tty/tty_buffer.c:502
 process_one_work kernel/workqueue.c:3396 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3479
 worker_thread+0x569/0x750 kernel/workqueue.c:3560
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000500 -> 0x00000033

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12 Comm: kworker/u8:0 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events_unbound flush_to_ldisc
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