Arch Linux

Description:
If a share on a Samba server is mounted using CIFS client (e.g. mount -t cifs -o guest //server/share /mnt/share) and then Samba server is restarted, then Samba server shows high CPU usage. Running "netstat -net | grep :445" on the Samba server shows a flood of connections. This can cause the Samba server to become slow or unresponsive.

Additional info:
* samba 4.5.8-1
* linux 4.10.8-1
* linux-lts 4.9.21-1
* linux-zen 4.10.8-1
* https://bugzilla.kernel.org/show_bug.cgi?id=194531

Steps to reproduce:
* Make sure smbd is not currently running:
# systemctl stop smbd
* Start a terminal window and run the following to start Samba server:
# mkdir -p /tmp/share
# cat > smb-test.conf << EOF
[share]
guest ok = yes
path = /tmp/share
EOF
# smbd -FS -s smb-test.conf

* Start another terminal window and run the following to mount the share:
# mkdir -p /tmp/share-mount
# mount -t cifs -o guest //localhost/share /tmp/share-mount
* Switch back to terminal that is running the server, restart the server:
Ctrl-C to stop server
# smbd -FS -s smb-test.conf

* Switch back to terminal window used to mount share
Wait 5 seconds
Run top command and notice high CPU usage for smbd. Press q to exit.
# top
Run netstat command repeatedly and notice there is an unusually large number of connection states to port :445 that is increasing rapidly
# netstat -net | grep :445 | wc -l
12236

Reverting commit b8c600120fc87d53642476f48c8055b38d6e14c7 for the kernel used on the client resolves the issue.