Merge branch 'inet-frags-avoid-possible-races-at-netns-dismantle'

Eric Dumazet says:

====================
inet: frags: avoid possible races at netns dismantle

This patch series fixes a race happening on netns dismantle with
frag queues. While rhashtable_free_and_destroy() is running,
concurrent timers might run inet_frag_kill() and attempt
rhashtable_remove_fast() calls. This is not allowed by
rhashtable logic.

Since I do not want to add expensive synchronize_rcu() calls
in the netns dismantle path, I had to no longer inline
netns_frags structures, but dynamically allocate them.

The ten first patches make this preparation, so that
the last patch clearly shows the fix.

As this patch series is not exactly trivial, I chose to
target 5.3. We will backport it once soaked a bit.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>