Merge branch 'concurrent_hash_tables'

Thomas Graf says:

====================
Lockless netlink_lookup() with new concurrent hash table

Netlink sockets are maintained in a hash table to allow efficient lookup
via the port ID for unicast messages. However, lookups currently require
a read lock to be taken. This series adds a new generic, resizable,
scalable, concurrent hash table based on the paper referenced in the first
patch. It then makes use of the new data type to implement lockless
netlink_lookup().

Patch 3/3 to convert nft_hash is included for reference but should be
merged via the netfilter tree. Inclusion in this series is to provide
context for the suggested API.

Against net-next since the initial user of the new hash table is in net/

Changes:
v4-v5:
 - use GFP_KERNEL to alloc Netlink buckets as suggested by Nikolay
   Aleksandrov
 - free nft hash element on removal as spotted by Nikolay Aleksandrov
   and Patrick McHardy
v3-v4:
 - fixed wrong shift assignment placement as spotted by Nikolay Aleksandrov
 - reverted default size of nft_hash to 4 as requested by Patrick McHardy,
   default size for other hash tables remains at 64 if no hint is given
 - fixed copyright as requested by Patrick McHardy
v2-v3:
 - fixed typo in nft_hash_destroy() when passing rhashtable handle
v1-v2:
 - fixed traversal off-by-one as spotted by Tobias Klauser
 - removed unlikely() from BUG_ON() as spotted by Josh Triplett
 - new 3rd patch to convert nft_hash to rhashtable
 - make rhashtable_insert() return void
 - nl_sk_hash_lock must be a mutex
 - fixed wrong name of rht_shrink_below_30()
 - exported symbols rht_grow_above_75() and rht_shrink_below_30()
 - allow table freeing with RCU callback
====================

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