[Bug 191040] New: em driver: netif hangs the system if interface is cabled and configured but there is no link

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=191040

            Bug ID: 191040
           Summary: em driver: netif hangs the system if interface is
                    cabled and configured but there is no link
           Product: Base System
           Version: 10.0-RELEASE
          Hardware: Any
                OS: Any
            Status: Needs Triage
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: jjasen at gmail.com

In a case where an em interface is configured via rc.conf, where the network
cable is plugged in, but there is no link on the cable, netif will hang the
system as it attempts configuration. I believe permanently, but only observed
for up to 15 minutes.

This does not happen when there is no cable connected, nor under normal
circumstances of having an rc.conf configuration entry and having a live
network cable.

ifconfig itself does not cause this problem, as I could plug the dead cable in
and assign addresses/bring up the interface to my hearts content.

I believe the problem is in /etc/rc.d/netif, as repeating the above experiment
and calling netif start em$dev-num causes it to hang. This is more curable than
on boot, as netif will then respond to shell commands to background the process
and responds to kill. On initial boot, there is no such luxury.

I also have not observed this case with other interface drivers.

While this scenario is a corner case, it can cause issues in situations where
you are provisioning new services, or preparing a server for new services.

http://lists.freebsd.org/pipermail/freebsd-net/2014-June/038932.html

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