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kernel:unregister_netdevice: waiting for lo to become free. Usage count = 1 SOLUTION VERIFIED - Updated July 6 2017 at 10:42 AM - English EnvironmentRed Hat Enterprise Linux 7.4 or earlierTCP connection over loopback interface loIssuekernel:unregister_netdevice: waiting for lo to become free. Usage count = 1Above message is logged constantly on console or in dmesg or /var/log/messages file or in systemd journalResolutionUpdate to RHEL 7.5 when available.Root CauseA bug resulted in the loopback device having a reference count which was increased but never decreased.This was resolved by upstream patch tcp: reset sk_rx_dst in tcp_disconnect() in Linux Kernel v4.12 and backported to RHEL 7.5 on Red Hat Private Bug 1467770.Diagnostic StepsUse the reproducer described at unregister_netdevice: waiting for lo to become free. Usage count = 1Run it in a netns once and delete the netns:Rawmake tcp-bugip netns add test1ip netns exec test1 ip link set dev lo upip netns exec test1 ./tcp-bugip netns del test1In the error condition kernel:unregister_netdevice: waiting for lo to become free. Usage count = 1 is printed on console and in dmesg.In the working condition, no error is printed and the netns is successfully deleted.