syzbot

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BUG: KCSAN: data-race in n_tty_check_unthrottle / n_tty_receive_buf_common

write to 0xffff88814dccc1e8 of 4 bytes by task 778 on cpu 1:
 tty_set_flow_change drivers/tty/tty.h:54 [inline]
 n_tty_check_unthrottle+0xd7/0x1c0 drivers/tty/n_tty.c:291
 n_tty_read+0xe8f/0x1180 drivers/tty/n_tty.c:2278
 iterate_tty_read drivers/tty/tty_io.c:852 [inline]
 tty_read+0x16e/0x3e0 drivers/tty/tty_io.c:927
 call_read_iter include/linux/fs.h:1845 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x39a/0x560 fs/read_write.c:470
 ksys_read+0xeb/0x1a0 fs/read_write.c:613
 __do_sys_read fs/read_write.c:623 [inline]
 __se_sys_read fs/read_write.c:621 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffff88814dccc1e8 of 4 bytes by task 794 on cpu 0:
 tty_set_flow_change drivers/tty/tty.h:54 [inline]
 n_tty_check_throttle drivers/tty/n_tty.c:261 [inline]
 n_tty_receive_buf_common+0xab4/0xb50 drivers/tty/n_tty.c:1730
 n_tty_receive_buf+0x2f/0x40 drivers/tty/n_tty.c:1740
 tiocsti+0x168/0x1c0 drivers/tty/tty_io.c:2292
 tty_ioctl+0x40f/0xbc0 drivers/tty/tty_io.c:2691
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000000 -> 0x00000002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 794 Comm: syz-executor.5 Tainted: G        W          6.3.0-rc7-syzkaller-00189-g2caeeb9d4a1b #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
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