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BUG: KCSAN: data-race in ppp_asynctty_receive / tty_set_termios

write to 0xffff88800b313910 of 4 bytes by task 20198 on cpu 1:
 unset_locked_termios drivers/tty/tty_ioctl.c:251 [inline]
 tty_set_termios+0xf1/0x8a0 drivers/tty/tty_ioctl.c:331
 set_termios+0x375/0x3b0 drivers/tty/tty_ioctl.c:414
 tty_mode_ioctl+0x573/0x670 drivers/tty/tty_ioctl.c:725
 ppp_asynctty_ioctl+0x229/0x300 drivers/net/ppp/ppp_async.c:326
 tty_ioctl+0xa97/0x10c0 drivers/tty/tty_io.c:2810
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88800b313910 of 4 bytes by task 59 on cpu 0:
 ppp_async_input drivers/net/ppp/ppp_async.c:912 [inline]
 ppp_asynctty_receive+0x760/0xdb0 drivers/net/ppp/ppp_async.c:351
 tty_ldisc_receive_buf+0xc6/0xf0 drivers/tty/tty_buffer.c:465
 tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:481 [inline]
 flush_to_ldisc+0x1c5/0x2c0 drivers/tty/tty_buffer.c:533
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 59 Comm: kworker/u4:2 Not tainted 5.12.0-rc6-syzkaller #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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