soft lockup - may be related to wireguard (backported)

[Alex Xu (Hello71)]

Excerpts from Jason A. Donenfeld's message of May 4, 2020 1:26 am:
> Are you routing wireguard over wireguard, or something interesting like that?
> 
> Is ipsec being used?
> 

This "DN2800MT" looks like an Atom board from 2012; are you trying to 
run a very large bandwidth through it? I think it's plausible that 
buffering could cause a large enough chunk of work for a slow CPU that 
the kernel could erroneously think that the code is stuck. I don't know 
why that would happen on the tx thread though, or why it would result in 
an RCU stall, seeing as only a single access is made under an RCU lock 
in this function...