tcp: Don't allocate tcp_death_row outside of struct netns_ipv4.

We will soon introduce an optional per-netns ehash and access hash
tables via net->ipv4.tcp_death_row->hashinfo instead of &tcp_hashinfo
in most places.

It could harm the fast path because dereferences of two fields in net
and tcp_death_row might incur two extra cache line misses.  To save one
dereference, let's place tcp_death_row back in netns_ipv4 and fetch
hashinfo via net->ipv4.tcp_death_row"."hashinfo.

Note tcp_death_row was initially placed in netns_ipv4, and commit
fbb8295248e1 ("tcp: allocate tcp_death_row outside of struct netns_ipv4")
changed it to a pointer so that we can fire TIME_WAIT timers after freeing
net.  However, we don't do so after commit 04c494e68a13 ("Revert "tcp/dccp:
get rid of inet_twsk_purge()""), so we need not define tcp_death_row as a
pointer.

Also, we move refcount_dec_and_test(&tw_refcount) from tcp_sk_exit() to
tcp_sk_exit_batch() as a debug check.

Signed-off-by: Kuniyuki Iwashima <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>

1 files changed, 2 insertions, 6 deletions

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 5490c285668b..4d7c110c772f 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -530,10 +530,9 @@ static struct ctl_table ipv4_table[] = {
 };
 
 static struct ctl_table ipv4_net_table[] = {
-	/* tcp_max_tw_buckets must be first in this table. */
 	{
 		.procname	= "tcp_max_tw_buckets",
-/*		.data		= &init_net.ipv4.tcp_death_row.sysctl_max_tw_buckets, */
+		.data		= &init_net.ipv4.tcp_death_row.sysctl_max_tw_buckets,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
@@ -1361,8 +1360,7 @@ static __net_init int ipv4_sysctl_init_net(struct net *net)
 		if (!table)
 			goto err_alloc;
 
-		/* skip first entry (sysctl_max_tw_buckets) */
-		for (i = 1; i < ARRAY_SIZE(ipv4_net_table) - 1; i++) {
+		for (i = 0; i < ARRAY_SIZE(ipv4_net_table) - 1; i++) {
 			if (table[i].data) {
 				/* Update the variables to point into
 				 * the current struct net
@@ -1377,8 +1375,6 @@ static __net_init int ipv4_sysctl_init_net(struct net *net)
 		}
 	}
 
-	table[0].data = &net->ipv4.tcp_death_row->sysctl_max_tw_buckets;
-
 	net->ipv4.ipv4_hdr = register_net_sysctl(net, "net/ipv4", table);
 	if (!net->ipv4.ipv4_hdr)
 		goto err_reg;