From: Dan Streetman <ddstr...@ieee.org> Date: Thu, 18 Jan 2018 16:14:26 -0500
> When a tcp socket is closed, if it detects that its net namespace is > exiting, close immediately and do not wait for FIN sequence. > > For normal sockets, a reference is taken to their net namespace, so it will > never exit while the socket is open. However, kernel sockets do not take a > reference to their net namespace, so it may begin exiting while the kernel > socket is still open. In this case if the kernel socket is a tcp socket, > it will stay open trying to complete its close sequence. The sock's dst(s) > hold a reference to their interface, which are all transferred to the > namespace's loopback interface when the real interfaces are taken down. > When the namespace tries to take down its loopback interface, it hangs > waiting for all references to the loopback interface to release, which > results in messages like: > > unregister_netdevice: waiting for lo to become free. Usage count = 1 > > These messages continue until the socket finally times out and closes. > Since the net namespace cleanup holds the net_mutex while calling its > registered pernet callbacks, any new net namespace initialization is > blocked until the current net namespace finishes exiting. > > After this change, the tcp socket notices the exiting net namespace, and > closes immediately, releasing its dst(s) and their reference to the > loopback interface, which lets the net namespace continue exiting. > > Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1711407 > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=97811 > Signed-off-by: Dan Streetman <ddstr...@canonical.com> Looks good, thanks for the detailed commit message and references to analysis in those bugzilla. Applied and queued up for -stable.
