nfs cache bug (when server delete the file ,nfs client can read file also)

Hi,everyone. I found a big bug abount nfs cache.

when server delete the file ,nfs client can read file also.

the following is the reproduce.

ip: 192.168.0.19 nfs-client
ip: 192.168.0.20 nfs-client
ip: 192.168.0.21 nfs-server

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/usr/bin/ssh -n 192.168.0.21 service nfs start
/usr/bin/ssh -n 192.168.0.21 /usr/sbin/rpc.idmapd
/usr/bin/ssh -n 192.168.0.19 /usr/sbin/rpc.idmapd
/usr/bin/ssh -n 192.168.0.20 /usr/sbin/rpc.idmapd
/usr/bin/ssh -n 192.168.0.21 "rm -rf /nfsroot; mkdir -p /nfsroot"
/usr/bin/ssh -n 192.168.0.21 /usr/sbin/exportfs -au
/usr/bin/ssh -n 192.168.0.21 /usr/sbin/exportfs -i -o insecure,no_root_squash,rw,fsid=0 *:/nfsroot

/usr/bin/ssh -n 192.168.0.19 test -d /nfsroot || (rm -rf /nfsroot; mkdir -p /nfsroot)
/usr/bin/ssh -n 192.168.0.20 test -d /nfsroot || (rm -rf /nfsroot; mkdir -p /nfsroot)

/usr/bin/ssh -n 192.168.0.19 umount /nfsroot /usr/bin/ssh -n 192.168.0.20 umount /nfsroot
cmd="echo \"hello world\" > /nfsroot/tmpfile" /usr/bin/ssh -n 192.168.0.21 $cmd
/usr/bin/ssh -n 192.168.0.21 mkdir /nfsroot/tmpdir /usr/bin/ssh -n 192.168.0.21 touch /nfsroot/tmpdir/tmpdfile /usr/bin/ssh -n 192.168.0.19 mount -t nfs4 192.168.0.21:/ /nfsroot /usr/bin/ssh -n 192.168.0.20 mount -t nfs4 192.168.0.21:/ /nfsroot /usr/bin/ssh -n 192.168.0.21 cat /nfsroot/tmpfile /usr/bin/ssh -n 192.168.0.21 ls -l /nfsroot/tmpdir /usr/bin/ssh -n 192.168.0.19 cat /nfsroot/tmpfile /usr/bin/ssh -n 192.168.0.19 ls -l /nfsroot/tmpdir /usr/bin/ssh -n 192.168.0.20 cat /nfsroot/tmpfile /usr/bin/ssh -n 192.168.0.20 ls -l /nfsroot/tmpdir /usr/bin/ssh -n 192.168.0.19 cat /nfsroot/tmpfile > /dev/null /usr/bin/ssh -n 192.168.0.20 cat /nfsroot/tmpfile > /dev/null /usr/bin/ssh -n 192.168.0.21 rm -rf /nfsroot/tmpfile echo -e "sleep 60~~~~~~~~\n"
sleep 60

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last: In 192.168.0.19 I do:

#cat /nfsroot/tmpfile <--the nfs server delete the file,but nfs client can read the file
hello world

I think when the nfs server delete the file ,
the server should notice the nfs client,
but the upstream kernel does't this.