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BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc900067bf278 of 8 bytes by task 30509 on cpu 1:
 __process_echoes+0x603/0x650 drivers/tty/n_tty.c:769
 flush_echoes drivers/tty/n_tty.c:830 [inline]
 __receive_buf drivers/tty/n_tty.c:1649 [inline]
 n_tty_receive_buf_common+0x1b80/0x1df0 drivers/tty/n_tty.c:1744
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1779
 tty_ldisc_receive_buf+0x61/0xf0 drivers/tty/tty_buffer.c:461
 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+0x1c5/0x2b0 drivers/tty/tty_buffer.c:533
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffffc900067bf278 of 8 bytes by task 1049 on cpu 0:
 process_echoes drivers/tty/n_tty.c:807 [inline]
 n_tty_write+0x147/0xae0 drivers/tty/n_tty.c:2321
 do_tty_write drivers/tty/tty_io.c:961 [inline]
 tty_write+0x3f9/0x610 drivers/tty/tty_io.c:1045
 vfs_write+0x21a/0x7c0 fs/read_write.c:603
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1049 Comm: syz-executor.3 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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