net: kernel BUG() in net/netns/generic.h:45

Hi all,

When an initialization of a network namespace in setup_net() fails, we
try to undo everything by executing each of the exit callbacks of every
namespace in the network.

The problem is, it might be possible that the net_generic array wasn't
initialized before we fail and try to undo everything. At that point,
some of the networks assume that since we're already calling the exit
callback, the net_generic structure is initialized and we hit the BUG()
in net/netns/generic.h:45 .

I'm not quite sure whether the right fix from the following three
options is, and would be happy to figure it out before fixing it:

 1. Don't assume net_generic was initialized in the exit callback, which
is a bit problematic since we can't query that nicely anyway (a
sub-option here would be adding an API to query whether the net_generic
structure is initialized.

 2. Remove the BUG(), switch it to a WARN() and let each subsystem
handle the case of NULL on it's own. While it sounds a bit wrong, it's
worth mentioning that that BUG() was initially added in an attempt to
fix an issue in CAIF, which was fixed in a completely different way
afterwards, so it's not strictly necessary here.

 3. Only call the exit callback for subsystems we have called the init
callback for.

Thanks!

-- 

Sasha.