[PATCH net-next 1/2] tcp: record last received ipv6 flowlabel

[PATCH net-next 1/2] tcp: record last received ipv6 flowlabel

[David Morley]

From: David Morley <morleyd@google.com>

In order to better estimate whether a data packet has been
retransmitted or is the result of a TLP, we save the last received
ipv6 flowlabel.

To make space for this field we resize the "ato" field in
inet_connection_sock as the current value of TCP_DELACK_MAX can be
fully contained in 8 bits and add a compile_time_assert ensuring this
field is the required size.

Signed-off-by: David Morley <morleyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Tested-by: David Morley <morleyd@google.com>
---
 include/net/inet_connection_sock.h |  5 ++++-
 include/net/tcp.h                  |  2 ++
 net/ipv4/tcp_input.c               | 15 +++++++++++++++
 net/ipv4/tcp_timer.c               |  2 +-
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 5d2fcc137b88..d6d9d1c1985a 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -114,7 +114,10 @@ struct inet_connection_sock {
 		__u8		  quick;	 /* Scheduled number of quick acks	   */
 		__u8		  pingpong;	 /* The session is interactive		   */
 		__u8		  retry;	 /* Number of attempts			   */
-		__u32		  ato;		 /* Predicted tick of soft clock	   */
+		#define ATO_BITS 8
+		__u32		  ato:ATO_BITS,	 /* Predicted tick of soft clock	   */
+				  lrcv_flowlabel:20, /* last received ipv6 flowlabel	   */
+				  unused:4;
 		unsigned long	  timeout;	 /* Currently scheduled timeout		   */
 		__u32		  lrcvtime;	 /* timestamp of last received data packet */
 		__u16		  last_seg_size; /* Size of last incoming segment	   */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 91688d0dadcd..8a3720c7d082 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -131,6 +131,8 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
 #define TCP_FIN_TIMEOUT_MAX (120 * HZ) /* max TCP_LINGER2 value (two minutes) */
 
 #define TCP_DELACK_MAX	((unsigned)(HZ/5))	/* maximal time to delay before sending an ACK */
+static_assert(1<<ATO_BITS > TCP_DELACK_MAX);
+
 #if HZ >= 100
 #define TCP_DELACK_MIN	((unsigned)(HZ/25))	/* minimal time to delay before sending an ACK */
 #define TCP_ATO_MIN	((unsigned)(HZ/25))
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 584825ddd0a0..abe7494361c0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -765,6 +765,16 @@ void tcp_rcv_space_adjust(struct sock *sk)
 	tp->rcvq_space.time = tp->tcp_mstamp;
 }
 
+static void tcp_save_lrcv_flowlabel(struct sock *sk, const struct sk_buff *skb)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	if (skb->protocol == htons(ETH_P_IPV6))
+		icsk->icsk_ack.lrcv_flowlabel = ntohl(ip6_flowlabel(ipv6_hdr(skb)));
+#endif
+}
+
 /* There is something which you must keep in mind when you analyze the
  * behavior of the tp->ato delayed ack timeout interval.  When a
  * connection starts up, we want to ack as quickly as possible.  The
@@ -813,6 +823,7 @@ static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 		}
 	}
 	icsk->icsk_ack.lrcvtime = now;
+	tcp_save_lrcv_flowlabel(sk, skb);
 
 	tcp_ecn_check_ce(sk, skb);
 
@@ -4506,6 +4517,9 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
 	    sk_rethink_txhash(sk))
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
+
+	/* Save last flowlabel after a spurious retrans. */
+	tcp_save_lrcv_flowlabel(sk, skb);
 }
 
 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
@@ -4822,6 +4836,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 	u32 seq, end_seq;
 	bool fragstolen;
 
+	tcp_save_lrcv_flowlabel(sk, skb);
 	tcp_ecn_check_ce(sk, skb);
 
 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 3f61c6a70a1f..0862b73dd3b5 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -322,7 +322,7 @@ void tcp_delack_timer_handler(struct sock *sk)
 	if (inet_csk_ack_scheduled(sk)) {
 		if (!inet_csk_in_pingpong_mode(sk)) {
 			/* Delayed ACK missed: inflate ATO. */
-			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
+			icsk->icsk_ack.ato = min_t(u32, icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 		} else {
 			/* Delayed ACK missed: leave pingpong mode and
 			 * deflate ATO.
-- 
2.42.0.582.g8ccd20d70d-goog

[PATCH net-next 2/2] tcp: change data receiver flowlabel after one dup

[David Morley]

From: David Morley <morleyd@google.com>

This commit changes the data receiver repath behavior to occur after
receiving a single duplicate. This can help recover ACK connectivity
quicker if a TLP was sent along a nonworking path.

For instance, consider the case where we have an initially nonworking
forward path and reverse path and subsequently switch to only working
forward paths. Before this patch we would have the following behavior.

+---------+--------+--------+----------+----------+----------+
| Event   | For FL | Rev FL | FP Works | RP Works | Data Del |
+---------+--------+--------+----------+----------+----------+
| Initial | A      | 1      | N        | N        | 0        |
+---------+--------+--------+----------+----------+----------+
| TLP     | A      | 1      | N        | N        | 0        |
+---------+--------+--------+----------+----------+----------+
| RTO 1   | B      | 1      | Y        | N        | 1        |
+---------+--------+--------+----------+----------+----------+
| RTO 2   | C      | 1      | Y        | N        | 2        |
+---------+--------+--------+----------+----------+----------+
| RTO 3   | D      | 2      | Y        | Y        | 3        |
+---------+--------+--------+----------+----------+----------+

This patch gets rid of at least RTO 3, avoiding additional unnecessary
repaths of a working forward path to a (potentially) nonworking one.

In addition, this commit changes the behavior to avoid repathing upon
rx of duplicate data if the local endpoint is in CA_Loss (in which
case the RTOs will already be changing the outgoing flowlabel).

Signed-off-by: David Morley <morleyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Tested-by: David Morley <morleyd@google.com>
---
 net/ipv4/tcp_input.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index abe7494361c0..f77fbdb3103d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4511,15 +4511,23 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 {
 	/* When the ACK path fails or drops most ACKs, the sender would
 	 * timeout and spuriously retransmit the same segment repeatedly.
-	 * The receiver remembers and reflects via DSACKs. Leverage the
-	 * DSACK state and change the txhash to re-route speculatively.
+	 * If it seems our ACKs are not reaching the other side,
+	 * based on receiving a duplicate data segment with new flowlabel
+	 * (suggesting the sender suffered an RTO), and we are not already
+	 * repathing due to our own RTO, then rehash the socket to repath our
+	 * packets.
 	 */
-	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
+#if IS_ENABLED(CONFIG_IPV6)
+	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss &&
+	    skb->protocol == htons(ETH_P_IPV6) &&
+	    (tcp_sk(sk)->inet_conn.icsk_ack.lrcv_flowlabel !=
+	     ntohl(ip6_flowlabel(ipv6_hdr(skb)))) &&
 	    sk_rethink_txhash(sk))
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
 
 	/* Save last flowlabel after a spurious retrans. */
 	tcp_save_lrcv_flowlabel(sk, skb);
+#endif
 }
 
 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
-- 
2.42.0.582.g8ccd20d70d-goog

Re: [PATCH net-next 1/2] tcp: record last received ipv6 flowlabel

[Eric Dumazet]

On Wed, Sep 27, 2023 at 8:28 PM David Morley <morleyd.kernel@gmail.com> wrote:
>
> From: David Morley <morleyd@google.com>
>
> In order to better estimate whether a data packet has been
> retransmitted or is the result of a TLP, we save the last received
> ipv6 flowlabel.
>
> To make space for this field we resize the "ato" field in
> inet_connection_sock as the current value of TCP_DELACK_MAX can be
> fully contained in 8 bits and add a compile_time_assert ensuring this
> field is the required size.
>
> Signed-off-by: David Morley <morleyd@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> Tested-by: David Morley <morleyd@google.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net-next 2/2] tcp: change data receiver flowlabel after one dup

[Eric Dumazet]

On Wed, Sep 27, 2023 at 8:28 PM David Morley <morleyd.kernel@gmail.com> wrote:
>
> From: David Morley <morleyd@google.com>
>
> This commit changes the data receiver repath behavior to occur after
> receiving a single duplicate. This can help recover ACK connectivity
> quicker if a TLP was sent along a nonworking path.
>
> For instance, consider the case where we have an initially nonworking
> forward path and reverse path and subsequently switch to only working
> forward paths. Before this patch we would have the following behavior.
>
> +---------+--------+--------+----------+----------+----------+
> | Event   | For FL | Rev FL | FP Works | RP Works | Data Del |
> +---------+--------+--------+----------+----------+----------+
> | Initial | A      | 1      | N        | N        | 0        |
> +---------+--------+--------+----------+----------+----------+
> | TLP     | A      | 1      | N        | N        | 0        |
> +---------+--------+--------+----------+----------+----------+
> | RTO 1   | B      | 1      | Y        | N        | 1        |
> +---------+--------+--------+----------+----------+----------+
> | RTO 2   | C      | 1      | Y        | N        | 2        |
> +---------+--------+--------+----------+----------+----------+
> | RTO 3   | D      | 2      | Y        | Y        | 3        |
> +---------+--------+--------+----------+----------+----------+
>
> This patch gets rid of at least RTO 3, avoiding additional unnecessary
> repaths of a working forward path to a (potentially) nonworking one.
>
> In addition, this commit changes the behavior to avoid repathing upon
> rx of duplicate data if the local endpoint is in CA_Loss (in which
> case the RTOs will already be changing the outgoing flowlabel).
>
> Signed-off-by: David Morley <morleyd@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> Tested-by: David Morley <morleyd@google.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net-next 1/2] tcp: record last received ipv6 flowlabel

[kernel test robot]

Hi David,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/David-Morley/tcp-change-data-receiver-flowlabel-after-one-dup/20230928-022955
base:   net-next/main
patch link:    https://lore.kernel.org/r/20230927182747.2005960-1-morleyd.kernel%40gmail.com
patch subject: [PATCH net-next 1/2] tcp: record last received ipv6 flowlabel
config: x86_64-rhel-8.3-rust (https://download.01.org/0day-ci/archive/20230929/202309291312.vJyV8G9L-lkp@intel.com/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230929/202309291312.vJyV8G9L-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309291312.vJyV8G9L-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> net/dccp/timer.c:199:25: warning: comparison of distinct pointer types ('typeof (icsk->icsk_ack.ato << 1) *' (aka 'int *') and 'typeof (icsk->icsk_rto) *' (aka 'unsigned int *')) [-Wcompare-distinct-pointer-types]
                           icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1,
                                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/minmax.h:68:19: note: expanded from macro 'min'
   #define min(x, y)       __careful_cmp(x, y, <)
                           ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/minmax.h:37:24: note: expanded from macro '__careful_cmp'
           __builtin_choose_expr(__safe_cmp(x, y), \
                                 ^~~~~~~~~~~~~~~~
   include/linux/minmax.h:27:4: note: expanded from macro '__safe_cmp'
                   (__typecheck(x, y) && __no_side_effects(x, y))
                    ^~~~~~~~~~~~~~~~~
   include/linux/minmax.h:21:28: note: expanded from macro '__typecheck'
           (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                      ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
   1 warning generated.


vim +199 net/dccp/timer.c

4ed800d02cfb63 Gerrit Renker 2006-11-13  168  
4ed800d02cfb63 Gerrit Renker 2006-11-13  169  /* This is the same as tcp_delack_timer, sans prequeue & mem_reclaim stuff */
59f379f9046a9e Kees Cook     2017-10-16  170  static void dccp_delack_timer(struct timer_list *t)
4ed800d02cfb63 Gerrit Renker 2006-11-13  171  {
59f379f9046a9e Kees Cook     2017-10-16  172  	struct inet_connection_sock *icsk =
59f379f9046a9e Kees Cook     2017-10-16  173  			from_timer(icsk, t, icsk_delack_timer);
59f379f9046a9e Kees Cook     2017-10-16  174  	struct sock *sk = &icsk->icsk_inet.sk;
4ed800d02cfb63 Gerrit Renker 2006-11-13  175  
4ed800d02cfb63 Gerrit Renker 2006-11-13  176  	bh_lock_sock(sk);
4ed800d02cfb63 Gerrit Renker 2006-11-13  177  	if (sock_owned_by_user(sk)) {
4ed800d02cfb63 Gerrit Renker 2006-11-13  178  		/* Try again later. */
02a1d6e7a6bb02 Eric Dumazet  2016-04-27  179  		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
4ed800d02cfb63 Gerrit Renker 2006-11-13  180  		sk_reset_timer(sk, &icsk->icsk_delack_timer,
4ed800d02cfb63 Gerrit Renker 2006-11-13  181  			       jiffies + TCP_DELACK_MIN);
4ed800d02cfb63 Gerrit Renker 2006-11-13  182  		goto out;
4ed800d02cfb63 Gerrit Renker 2006-11-13  183  	}
4ed800d02cfb63 Gerrit Renker 2006-11-13  184  
4ed800d02cfb63 Gerrit Renker 2006-11-13  185  	if (sk->sk_state == DCCP_CLOSED ||
4ed800d02cfb63 Gerrit Renker 2006-11-13  186  	    !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
4ed800d02cfb63 Gerrit Renker 2006-11-13  187  		goto out;
4ed800d02cfb63 Gerrit Renker 2006-11-13  188  	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
4ed800d02cfb63 Gerrit Renker 2006-11-13  189  		sk_reset_timer(sk, &icsk->icsk_delack_timer,
4ed800d02cfb63 Gerrit Renker 2006-11-13  190  			       icsk->icsk_ack.timeout);
4ed800d02cfb63 Gerrit Renker 2006-11-13  191  		goto out;
4ed800d02cfb63 Gerrit Renker 2006-11-13  192  	}
4ed800d02cfb63 Gerrit Renker 2006-11-13  193  
4ed800d02cfb63 Gerrit Renker 2006-11-13  194  	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
4ed800d02cfb63 Gerrit Renker 2006-11-13  195  
4ed800d02cfb63 Gerrit Renker 2006-11-13  196  	if (inet_csk_ack_scheduled(sk)) {
31954cd8bb6670 Wei Wang      2019-01-25  197  		if (!inet_csk_in_pingpong_mode(sk)) {
4ed800d02cfb63 Gerrit Renker 2006-11-13  198  			/* Delayed ACK missed: inflate ATO. */
4ed800d02cfb63 Gerrit Renker 2006-11-13 @199  			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1,
4ed800d02cfb63 Gerrit Renker 2006-11-13  200  						 icsk->icsk_rto);
4ed800d02cfb63 Gerrit Renker 2006-11-13  201  		} else {
4ed800d02cfb63 Gerrit Renker 2006-11-13  202  			/* Delayed ACK missed: leave pingpong mode and
4ed800d02cfb63 Gerrit Renker 2006-11-13  203  			 * deflate ATO.
4ed800d02cfb63 Gerrit Renker 2006-11-13  204  			 */
31954cd8bb6670 Wei Wang      2019-01-25  205  			inet_csk_exit_pingpong_mode(sk);
4ed800d02cfb63 Gerrit Renker 2006-11-13  206  			icsk->icsk_ack.ato = TCP_ATO_MIN;
4ed800d02cfb63 Gerrit Renker 2006-11-13  207  		}
4ed800d02cfb63 Gerrit Renker 2006-11-13  208  		dccp_send_ack(sk);
02a1d6e7a6bb02 Eric Dumazet  2016-04-27  209  		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
4ed800d02cfb63 Gerrit Renker 2006-11-13  210  	}
4ed800d02cfb63 Gerrit Renker 2006-11-13  211  out:
4ed800d02cfb63 Gerrit Renker 2006-11-13  212  	bh_unlock_sock(sk);
4ed800d02cfb63 Gerrit Renker 2006-11-13  213  	sock_put(sk);
4ed800d02cfb63 Gerrit Renker 2006-11-13  214  }
4ed800d02cfb63 Gerrit Renker 2006-11-13  215  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki