net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls

RCU was added to UDP lookups, using a fast infrastructure :
- sockets kmem_cache use SLAB_DESTROY_BY_RCU and dont pay the
  price of call_rcu() at freeing time.
- hlist_nulls permits to use few memory barriers.

This patch uses same infrastructure for TCP/DCCP established
and timewait sockets.

Thanks to SLAB_DESTROY_BY_RCU, no slowdown for applications
using short lived TCP connections. A followup patch, converting
rwlocks to spinlocks will even speedup this case.

__inet_lookup_established() is pretty fast now we dont have to
dirty a contended cache line (read_lock/read_unlock)

Only established and timewait hashtable are converted to RCU
(bind table and listen table are still using traditional locking)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f60a5917e54d..044224a341eb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2707,8 +2707,8 @@ void __init tcp_init(void)
                                         thash_entries ? 0 : 512 * 1024);
         tcp_hashinfo.ehash_size = 1 << tcp_hashinfo.ehash_size;
         for (i = 0; i < tcp_hashinfo.ehash_size; i++) {
-                INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].chain);
-                INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].twchain);
+                INIT_HLIST_NULLS_HEAD(&tcp_hashinfo.ehash[i].chain, i);
+                INIT_HLIST_NULLS_HEAD(&tcp_hashinfo.ehash[i].twchain, i);
         }
         if (inet_ehash_locks_alloc(&tcp_hashinfo))
                 panic("TCP: failed to alloc ehash_locks");