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tcp: remove tcp_tw_recycle

The tcp_tw_recycle was already broken for connections
behind NAT, since the per-destination timestamp is not
monotonically increasing for multiple machines behind
a single destination address.

After the randomization of TCP timestamp offsets
in commit 8a5bd45f6616 (tcp: randomize tcp timestamp offsets
for each connection), the tcp_tw_recycle is broken for all
types of connections for the same reason: the timestamps
received from a single machine is not monotonically increasing,
anymore.

Remove tcp_tw_recycle, since it is not functional. Also, remove
the PAWSPassive SNMP counter since it is only used for
tcp_tw_recycle, and simplify tcp_v4_route_req and tcp_v6_route_req
since the strict argument is only set when tcp_tw_recycle is
enabled.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Cc: Lutz Vieweg <lvml@5t9.de>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
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soheilhy authored and davem330 committed Mar 15, 2017
1 parent d82bae1 commit 4396e46187ca5070219b81773c4e65088dac50cc
@@ -640,11 +640,6 @@ tcp_tso_win_divisor - INTEGER
building larger TSO frames.
Default: 3

tcp_tw_recycle - BOOLEAN
Enable fast recycling TIME-WAIT sockets. Default value is 0.
It should not be changed without advice/request of technical
experts.

tcp_tw_reuse - BOOLEAN
Allow to reuse TIME-WAIT sockets for new connections when it is
safe from protocol viewpoint. Default value is 0.
@@ -33,7 +33,6 @@ struct inet_timewait_death_row {
atomic_t tw_count;

struct inet_hashinfo *hashinfo ____cacheline_aligned_in_smp;
int sysctl_tw_recycle;
int sysctl_max_tw_buckets;
};

@@ -1810,8 +1810,7 @@ struct tcp_request_sock_ops {
__u16 *mss);
#endif
struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,
const struct request_sock *req,
bool *strict);
const struct request_sock *req);
__u32 (*init_seq_tsoff)(const struct sk_buff *skb, u32 *tsoff);
int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
struct flowi *fl, struct request_sock *req,
@@ -177,7 +177,6 @@ enum
LINUX_MIB_TIMEWAITED, /* TimeWaited */
LINUX_MIB_TIMEWAITRECYCLED, /* TimeWaitRecycled */
LINUX_MIB_TIMEWAITKILLED, /* TimeWaitKilled */
LINUX_MIB_PAWSPASSIVEREJECTED, /* PAWSPassiveRejected */
LINUX_MIB_PAWSACTIVEREJECTED, /* PAWSActiveRejected */
LINUX_MIB_PAWSESTABREJECTED, /* PAWSEstabRejected */
LINUX_MIB_DELAYEDACKS, /* DelayedACKs */
@@ -199,7 +199,6 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TW", LINUX_MIB_TIMEWAITED),
SNMP_MIB_ITEM("TWRecycled", LINUX_MIB_TIMEWAITRECYCLED),
SNMP_MIB_ITEM("TWKilled", LINUX_MIB_TIMEWAITKILLED),
SNMP_MIB_ITEM("PAWSPassive", LINUX_MIB_PAWSPASSIVEREJECTED),
SNMP_MIB_ITEM("PAWSActive", LINUX_MIB_PAWSACTIVEREJECTED),
SNMP_MIB_ITEM("PAWSEstab", LINUX_MIB_PAWSESTABREJECTED),
SNMP_MIB_ITEM("DelayedACKs", LINUX_MIB_DELAYEDACKS),
@@ -980,13 +980,6 @@ static struct ctl_table ipv4_net_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "tcp_tw_recycle",
.data = &init_net.ipv4.tcp_death_row.sysctl_tw_recycle,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "tcp_max_syn_backlog",
.data = &init_net.ipv4.sysctl_max_syn_backlog,
@@ -6327,31 +6327,11 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
af_ops->init_seq_tsoff(skb, &tcp_rsk(req)->ts_off);

if (!want_cookie && !isn) {
/* VJ's idea. We save last timestamp seen
* from the destination in peer table, when entering
* state TIME-WAIT, and check against it before
* accepting new connection request.
*
* If "isn" is not zero, this request hit alive
* timewait bucket, so that all the necessary checks
* are made in the function processing timewait state.
*/
if (net->ipv4.tcp_death_row.sysctl_tw_recycle) {
bool strict;

dst = af_ops->route_req(sk, &fl, req, &strict);

if (dst && strict &&
!tcp_peer_is_proven(req, dst)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
goto drop_and_release;
}
}
/* Kill the following clause, if you dislike this way. */
else if (!net->ipv4.sysctl_tcp_syncookies &&
(net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
(net->ipv4.sysctl_max_syn_backlog >> 2)) &&
!tcp_peer_is_proven(req, dst)) {
if (!net->ipv4.sysctl_tcp_syncookies &&
(net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
(net->ipv4.sysctl_max_syn_backlog >> 2)) &&
!tcp_peer_is_proven(req, dst)) {
/* Without syncookies last quarter of
* backlog is filled with destinations,
* proven to be alive.
@@ -6367,7 +6347,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
isn = af_ops->init_seq_tsoff(skb, &tcp_rsk(req)->ts_off);
}
if (!dst) {
dst = af_ops->route_req(sk, &fl, req, NULL);
dst = af_ops->route_req(sk, &fl, req);
if (!dst)
goto drop_and_free;
}
@@ -1213,19 +1213,9 @@ static void tcp_v4_init_req(struct request_sock *req,

static struct dst_entry *tcp_v4_route_req(const struct sock *sk,
struct flowi *fl,
const struct request_sock *req,
bool *strict)
const struct request_sock *req)
{
struct dst_entry *dst = inet_csk_route_req(sk, &fl->u.ip4, req);

if (strict) {
if (fl->u.ip4.daddr == inet_rsk(req)->ir_rmt_addr)
*strict = true;
else
*strict = false;
}

return dst;
return inet_csk_route_req(sk, &fl->u.ip4, req);
}

struct request_sock_ops tcp_request_sock_ops __read_mostly = {
@@ -2462,7 +2452,6 @@ static int __net_init tcp_sk_init(struct net *net)
net->ipv4.sysctl_tcp_tw_reuse = 0;

cnt = tcp_hashinfo.ehash_mask + 1;
net->ipv4.tcp_death_row.sysctl_tw_recycle = 0;
net->ipv4.tcp_death_row.sysctl_max_tw_buckets = (cnt + 1) / 2;
net->ipv4.tcp_death_row.hashinfo = &tcp_hashinfo;

@@ -722,11 +722,8 @@ static void tcp_v6_init_req(struct request_sock *req,

static struct dst_entry *tcp_v6_route_req(const struct sock *sk,
struct flowi *fl,
const struct request_sock *req,
bool *strict)
const struct request_sock *req)
{
if (strict)
*strict = true;
return inet6_csk_route_req(sk, &fl->u.ip6, req, IPPROTO_TCP);
}

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