Continuation of failed RPC request after unmount

Hi all,

I'm debugging some likely buggy network device driver. Let's say the 
driver erroneously looses some packets (under certain conditions). One 
of important tests is being able to mount and use NFS share (as a 
client). I'm currently using kernel 4.14.221 and NFS v3 in UDP mode.

While testing, I've noticed some strange NFS behaviour. If some NFS 
request (file read) obtains no response (let's suppose due to 
connectivity issue), such request will be resent periodically (in hope 
to eventually succeed). This is expected. Now I observe, that after I 
unmount the NFS share (successfully), the failed requests still keep 
being resent, apparently infinitely (Confirmed by e.g. Wireshark), 
surviving also ifdown and ifup. So basically, I've found no way to get 
rid of them other than reboot.
Is this a known behaviour? Is it by design? Does it make any sense?


Thank you,

Regards,
Nikolai