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>

3 files changed, 4 insertions, 2 deletions

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 528baa2e5be4..d1dd95289b89 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -938,6 +938,7 @@ static struct proto dccp_v4_prot = {
         .orphan_count           = &dccp_orphan_count,
         .max_header             = MAX_DCCP_HEADER,
         .obj_size               = sizeof(struct dccp_sock),
+        .slab_flags             = SLAB_DESTROY_BY_RCU,
         .rsk_prot               = &dccp_request_sock_ops,
         .twsk_prot              = &dccp_timewait_sock_ops,
         .h.hashinfo             = &dccp_hashinfo,
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 4aa1148cdb20..f033e845bb07 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -1140,6 +1140,7 @@ static struct proto dccp_v6_prot = {
         .orphan_count      = &dccp_orphan_count,
         .max_header        = MAX_DCCP_HEADER,
         .obj_size          = sizeof(struct dccp6_sock),
+        .slab_flags        = SLAB_DESTROY_BY_RCU,
         .rsk_prot          = &dccp6_request_sock_ops,
         .twsk_prot         = &dccp6_timewait_sock_ops,
         .h.hashinfo        = &dccp_hashinfo,
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 46cb3490d48e..1117d4d8c8f1 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1090,8 +1090,8 @@ static int __init dccp_init(void)
         }
 
         for (i = 0; i < dccp_hashinfo.ehash_size; i++) {
-                INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].chain);
-                INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].twchain);
+                INIT_HLIST_NULLS_HEAD(&dccp_hashinfo.ehash[i].chain, i);
+                INIT_HLIST_NULLS_HEAD(&dccp_hashinfo.ehash[i].twchain, i);
         }
 
         if (inet_ehash_locks_alloc(&dccp_hashinfo))