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BUG: KCSAN: data-race in commit_echoes / process_echoes

read to 0xffffc90001605028 of 8 bytes by task 13663 on cpu 0:
 process_echoes+0x3f/0x100 drivers/tty/n_tty.c:806
 n_tty_write+0x132/0x9f0 drivers/tty/n_tty.c:2319
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x2fb/0x4e0 drivers/tty/tty_io.c:1046
 do_loop_readv_writev fs/read_write.c:717 [inline]
 do_loop_readv_writev fs/read_write.c:701 [inline]
 do_iter_write fs/read_write.c:972 [inline]
 do_iter_write+0x34b/0x3c0 fs/read_write.c:951
 vfs_writev+0x118/0x1c0 fs/read_write.c:1015
 do_writev+0xe3/0x250 fs/read_write.c:1058
 __do_sys_writev fs/read_write.c:1131 [inline]
 __se_sys_writev fs/read_write.c:1128 [inline]
 __x64_sys_writev+0x4e/0x60 fs/read_write.c:1128
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffffc90001605028 of 8 bytes by task 8198 on cpu 1:
 commit_echoes+0x5c/0x170 drivers/tty/n_tty.c:780
 n_tty_receive_char_fast drivers/tty/n_tty.c:1449 [inline]
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1609 [inline]
 __receive_buf drivers/tty/n_tty.c:1644 [inline]
 n_tty_receive_buf_common+0x1741/0x1b00 drivers/tty/n_tty.c:1742
 n_tty_receive_buf2+0x3d/0x60 drivers/tty/n_tty.c:1777
 tty_ldisc_receive_buf+0x71/0xf0 drivers/tty/tty_buffer.c:461
 tty_port_default_receive_buf+0x87/0xd0 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:481 [inline]
 flush_to_ldisc+0x1d5/0x260 drivers/tty/tty_buffer.c:533
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8198 Comm: kworker/u4:5 Not tainted 5.5.0-rc1-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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