# Assertion in_epoch failed when trying to implement Multipath TCP.



## ray_guo (Aug 7, 2022)

Hello,

I am trying to implement Multipath TCP into Freebsd version 13.1. I am using VMware virtual machie. (I am quite new to Freebsd)

When i do `pkg update`, the handshake phase seems okay, but when during the subflow, a kerenel panic happens: Assertion in_epoch failed at tcp_out.c:638(screenshots below)

Here are the epoch track message.






and here are the kernel panic:





tcp_out.c:638 is 
	
	



```
NET_EPOCH_ASSERT();
```

I have read through the epoch(9) but still have no idea what's going on, I know this requires a lot of effect to fix. So if I can get some hints based on your experience like where I should look at or what might be the reason I'd be very grateful. In case of you want to see the code, this is my git repo: https://github.com/RayGuo-ergou/freebsd-src/tree/mptcp-version13
Thanks


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