linux-stable.git/net/ipv4/tcp_input.c, branch linux-5.7.y Linux kernel stable tree tcp: apply a floor of 1 for RTT samples from TCP timestamps 2020-08-11T13:35:42+00:00 Jianfeng Wang jfwang@google.com 2020-07-30T23:49:16+00:00 4880b3091b49ee7c3799ec0dde5f61f6f90ccda6 [ Upstream commit 730e700e2c19d87e578ff0e7d8cb1d4a02b036d2 ] For retransmitted packets, TCP needs to resort to using TCP timestamps for computing RTT samples. In the common case where the data and ACK fall in the same 1-millisecond interval, TCP senders with millisecond- granularity TCP timestamps compute a ca_rtt_us of 0. This ca_rtt_us of 0 propagates to rs->rtt_us. This value of 0 can cause performance problems for congestion control modules. For example, in BBR, the zero min_rtt sample can bring the min_rtt and BDP estimate down to 0, reduce snd_cwnd and result in a low throughput. It would be hard to mitigate this with filtering in the congestion control module, because the proper floor to apply would depend on the method of RTT sampling (using timestamp options or internally-saved transmission timestamps). This fix applies a floor of 1 for the RTT sample delta from TCP timestamps, so that seq_rtt_us, ca_rtt_us, and rs->rtt_us will be at least 1 * (USEC_PER_SEC / TCP_TS_HZ). Note that the receiver RTT computation in tcp_rcv_rtt_measure() and min_rtt computation in tcp_update_rtt_min() both already apply a floor of 1 timestamp tick, so this commit makes the code more consistent in avoiding this edge case of a value of 0. Signed-off-by: Jianfeng Wang <jfwang@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Kevin Yang <yyd@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
[ Upstream commit 730e700e2c19d87e578ff0e7d8cb1d4a02b036d2 ]

For retransmitted packets, TCP needs to resort to using TCP timestamps
for computing RTT samples. In the common case where the data and ACK
fall in the same 1-millisecond interval, TCP senders with millisecond-
granularity TCP timestamps compute a ca_rtt_us of 0. This ca_rtt_us
of 0 propagates to rs->rtt_us.

This value of 0 can cause performance problems for congestion control
modules. For example, in BBR, the zero min_rtt sample can bring the
min_rtt and BDP estimate down to 0, reduce snd_cwnd and result in a
low throughput. It would be hard to mitigate this with filtering in
the congestion control module, because the proper floor to apply would
depend on the method of RTT sampling (using timestamp options or
internally-saved transmission timestamps).

This fix applies a floor of 1 for the RTT sample delta from TCP
timestamps, so that seq_rtt_us, ca_rtt_us, and rs->rtt_us will be at
least 1 * (USEC_PER_SEC / TCP_TS_HZ).

Note that the receiver RTT computation in tcp_rcv_rtt_measure() and
min_rtt computation in tcp_update_rtt_min() both already apply a floor
of 1 timestamp tick, so this commit makes the code more consistent in
avoiding this edge case of a value of 0.

Signed-off-by: Jianfeng Wang <jfwang@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Kevin Yang <yyd@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tcp: allow at most one TLP probe per flight 2020-07-31T16:47:15+00:00 Yuchung Cheng ycheng@google.com 2020-07-23T19:00:06+00:00 64ad87bfab4aab750b66c31c482488f825aeaff5 [ Upstream commit 76be93fc0702322179bb0ea87295d820ee46ad14 ] Previously TLP may send multiple probes of new data in one flight. This happens when the sender is cwnd limited. After the initial TLP containing new data is sent, the sender receives another ACK that acks partial inflight. It may re-arm another TLP timer to send more, if no further ACK returns before the next TLP timeout (PTO) expires. The sender may send in theory a large amount of TLP until send queue is depleted. This only happens if the sender sees such irregular uncommon ACK pattern. But it is generally undesirable behavior during congestion especially. The original TLP design restrict only one TLP probe per inflight as published in "Reducing Web Latency: the Virtue of Gentle Aggression", SIGCOMM 2013. This patch changes TLP to send at most one probe per inflight. Note that if the sender is app-limited, TLP retransmits old data and did not have this issue. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
[ Upstream commit 76be93fc0702322179bb0ea87295d820ee46ad14 ]

Previously TLP may send multiple probes of new data in one
flight. This happens when the sender is cwnd limited. After the
initial TLP containing new data is sent, the sender receives another
ACK that acks partial inflight.  It may re-arm another TLP timer
to send more, if no further ACK returns before the next TLP timeout
(PTO) expires. The sender may send in theory a large amount of TLP
until send queue is depleted. This only happens if the sender sees
such irregular uncommon ACK pattern. But it is generally undesirable
behavior during congestion especially.

The original TLP design restrict only one TLP probe per inflight as
published in "Reducing Web Latency: the Virtue of Gentle Aggression",
SIGCOMM 2013. This patch changes TLP to send at most one probe
per inflight.

Note that if the sender is app-limited, TLP retransmits old data
and did not have this issue.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tcp: fix SO_RCVLOWAT possible hangs under high mem pressure 2020-07-22T07:33:56+00:00 Eric Dumazet edumazet@google.com 2020-06-30T20:51:28+00:00 43e3007dbd6c44ee5285ac40a45af8c42da613c0 [ Upstream commit ba3bb0e76ccd464bb66665a1941fabe55dadb3ba ] Whenever tcp_try_rmem_schedule() returns an error, we are under trouble and should make sure to wakeup readers so that they can drain socket queues and eventually make room. Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users") Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
[ Upstream commit ba3bb0e76ccd464bb66665a1941fabe55dadb3ba ]

Whenever tcp_try_rmem_schedule() returns an error, we are under
trouble and should make sure to wakeup readers so that they
can drain socket queues and eventually make room.

Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tcp: grow window for OOO packets only for SACK flows 2020-06-30T19:35:48+00:00 Eric Dumazet edumazet@google.com 2020-06-16T03:37:07+00:00 bf780119617797b5690e999e59a64ad79a572374 [ Upstream commit 662051215c758ae8545451628816204ed6cd372d ] Back in 2013, we made a change that broke fast retransmit for non SACK flows. Indeed, for these flows, a sender needs to receive three duplicate ACK before starting fast retransmit. Sending ACK with different receive window do not count. Even if enabling SACK is strongly recommended these days, there still are some cases where it has to be disabled. Not increasing the window seems better than having to rely on RTO. After the fix, following packetdrill test gives : // Initialize connection 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7> +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 8> +0 < . 1:1(0) ack 1 win 514 +0 accept(3, ..., ...) = 4 +0 < . 1:1001(1000) ack 1 win 514 // Quick ack +0 > . 1:1(0) ack 1001 win 264 +0 < . 2001:3001(1000) ack 1 win 514 // DUPACK : Normally we should not change the window +0 > . 1:1(0) ack 1001 win 264 +0 < . 3001:4001(1000) ack 1 win 514 // DUPACK : Normally we should not change the window +0 > . 1:1(0) ack 1001 win 264 +0 < . 4001:5001(1000) ack 1 win 514 // DUPACK : Normally we should not change the window +0 > . 1:1(0) ack 1001 win 264 +0 < . 1001:2001(1000) ack 1 win 514 // Hole is repaired. +0 > . 1:1(0) ack 5001 win 272 Fixes: 4e4f1fc22681 ("tcp: properly increase rcv_ssthresh for ofo packets") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
[ Upstream commit 662051215c758ae8545451628816204ed6cd372d ]

Back in 2013, we made a change that broke fast retransmit
for non SACK flows.

Indeed, for these flows, a sender needs to receive three duplicate
ACK before starting fast retransmit. Sending ACK with different
receive window do not count.

Even if enabling SACK is strongly recommended these days,
there still are some cases where it has to be disabled.

Not increasing the window seems better than having to
rely on RTO.

After the fix, following packetdrill test gives :

// Initialize connection
    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
   +0 bind(3, ..., ...) = 0
   +0 listen(3, 1) = 0

   +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
   +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 8>
   +0 < . 1:1(0) ack 1 win 514

   +0 accept(3, ..., ...) = 4

   +0 < . 1:1001(1000) ack 1 win 514
// Quick ack
   +0 > . 1:1(0) ack 1001 win 264

   +0 < . 2001:3001(1000) ack 1 win 514
// DUPACK : Normally we should not change the window
   +0 > . 1:1(0) ack 1001 win 264

   +0 < . 3001:4001(1000) ack 1 win 514
// DUPACK : Normally we should not change the window
   +0 > . 1:1(0) ack 1001 win 264

   +0 < . 4001:5001(1000) ack 1 win 514
// DUPACK : Normally we should not change the window
    +0 > . 1:1(0) ack 1001 win 264

   +0 < . 1001:2001(1000) ack 1 win 514
// Hole is repaired.
   +0 > . 1:1(0) ack 5001 win 272

Fixes: 4e4f1fc22681 ("tcp: properly increase rcv_ssthresh for ofo packets")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tcp: don't ignore ECN CWR on pure ACK 2020-06-30T19:35:48+00:00 Denis Kirjanov kda@linux-powerpc.org 2020-06-25T11:51:06+00:00 4df64b5a5ea7674012bc0ac6c8921398a23bc7f0 [ Upstream commit 2570284060b48f3f79d8f1a2698792f36c385e9a ] there is a problem with the CWR flag set in an incoming ACK segment and it leads to the situation when the ECE flag is latched forever the following packetdrill script shows what happens: // Stack receives incoming segments with CE set +0.1 <[ect0] . 11001:12001(1000) ack 1001 win 65535 +0.0 <[ce] . 12001:13001(1000) ack 1001 win 65535 +0.0 <[ect0] P. 13001:14001(1000) ack 1001 win 65535 // Stack repsonds with ECN ECHO +0.0 >[noecn] . 1001:1001(0) ack 12001 +0.0 >[noecn] E. 1001:1001(0) ack 13001 +0.0 >[noecn] E. 1001:1001(0) ack 14001 // Write a packet +0.1 write(3, ..., 1000) = 1000 +0.0 >[ect0] PE. 1001:2001(1000) ack 14001 // Pure ACK received +0.01 <[noecn] W. 14001:14001(0) ack 2001 win 65535 // Since CWR was sent, this packet should NOT have ECE set +0.1 write(3, ..., 1000) = 1000 +0.0 >[ect0] P. 2001:3001(1000) ack 14001 // but Linux will still keep ECE latched here, with packetdrill // flagging a missing ECE flag, expecting // >[ect0] PE. 2001:3001(1000) ack 14001 // in the script In the situation above we will continue to send ECN ECHO packets and trigger the peer to reduce the congestion window. To avoid that we can check CWR on pure ACKs received. v3: - Add a sequence check to avoid sending an ACK to an ACK v2: - Adjusted the comment - move CWR check before checking for unacknowledged packets Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
[ Upstream commit 2570284060b48f3f79d8f1a2698792f36c385e9a ]

there is a problem with the CWR flag set in an incoming ACK segment
and it leads to the situation when the ECE flag is latched forever

the following packetdrill script shows what happens:

// Stack receives incoming segments with CE set
+0.1 <[ect0]  . 11001:12001(1000) ack 1001 win 65535
+0.0 <[ce]    . 12001:13001(1000) ack 1001 win 65535
+0.0 <[ect0] P. 13001:14001(1000) ack 1001 win 65535

// Stack repsonds with ECN ECHO
+0.0 >[noecn]  . 1001:1001(0) ack 12001
+0.0 >[noecn] E. 1001:1001(0) ack 13001
+0.0 >[noecn] E. 1001:1001(0) ack 14001

// Write a packet
+0.1 write(3, ..., 1000) = 1000
+0.0 >[ect0] PE. 1001:2001(1000) ack 14001

// Pure ACK received
+0.01 <[noecn] W. 14001:14001(0) ack 2001 win 65535

// Since CWR was sent, this packet should NOT have ECE set

+0.1 write(3, ..., 1000) = 1000
+0.0 >[ect0]  P. 2001:3001(1000) ack 14001
// but Linux will still keep ECE latched here, with packetdrill
// flagging a missing ECE flag, expecting
// >[ect0] PE. 2001:3001(1000) ack 14001
// in the script

In the situation above we will continue to send ECN ECHO packets
and trigger the peer to reduce the congestion window. To avoid that
we can check CWR on pure ACKs received.

v3:
- Add a sequence check to avoid sending an ACK to an ACK

v2:
- Adjusted the comment
- move CWR check before checking for unacknowledged packets

Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tcp: fix SO_RCVLOWAT hangs with fat skbs 2020-05-12T19:49:47+00:00 Eric Dumazet edumazet@google.com 2020-05-12T13:54:30+00:00 24adbc1676af4e134e709ddc7f34cf2adc2131e4 We autotune rcvbuf whenever SO_RCVLOWAT is set to account for 100% overhead in tcp_set_rcvlowat() This works well when skb->len/skb->truesize ratio is bigger than 0.5 But if we receive packets with small MSS, we can end up in a situation where not enough bytes are available in the receive queue to satisfy RCVLOWAT setting. As our sk_rcvbuf limit is hit, we send zero windows in ACK packets, preventing remote peer from sending more data. Even autotuning does not help, because it only triggers at the time user process drains the queue. If no EPOLLIN is generated, this can not happen. Note poll() has a similar issue, after commit c7004482e8dc ("tcp: Respect SO_RCVLOWAT in tcp_poll().") Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users") Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
We autotune rcvbuf whenever SO_RCVLOWAT is set to account for 100%
overhead in tcp_set_rcvlowat()

This works well when skb->len/skb->truesize ratio is bigger than 0.5

But if we receive packets with small MSS, we can end up in a situation
where not enough bytes are available in the receive queue to satisfy
RCVLOWAT setting.
As our sk_rcvbuf limit is hit, we send zero windows in ACK packets,
preventing remote peer from sending more data.

Even autotuning does not help, because it only triggers at the time
user process drains the queue. If no EPOLLIN is generated, this
can not happen.

Note poll() has a similar issue, after commit
c7004482e8dc ("tcp: Respect SO_RCVLOWAT in tcp_poll().")

Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
mptcp: move option parsing into mptcp_incoming_options() 2020-04-30T19:23:22+00:00 Paolo Abeni pabeni@redhat.com 2020-04-30T13:01:52+00:00 cfde141ea3faa30e362bbdb5c28001bbbdb0b8e0 The mptcp_options_received structure carries several per packet flags (mp_capable, mp_join, etc.). Such fields must be cleared on each packet, even on dropped ones or packet not carrying any MPTCP options, but the current mptcp code clears them only on TCP option reset. On several races/corner cases we end-up with stray bits in incoming options, leading to WARN_ON splats. e.g.: [ 171.164906] Bad mapping: ssn=32714 map_seq=1 map_data_len=32713 [ 171.165006] WARNING: CPU: 1 PID: 5026 at net/mptcp/subflow.c:533 warn_bad_map (linux-mptcp/net/mptcp/subflow.c:533 linux-mptcp/net/mptcp/subflow.c:531) [ 171.167632] Modules linked in: ip6_vti ip_vti ip_gre ipip sit tunnel4 ip_tunnel geneve ip6_udp_tunnel udp_tunnel macsec macvtap tap ipvlan macvlan 8021q garp mrp xfrm_interface veth netdevsim nlmon dummy team bonding vcan bridge stp llc ip6_gre gre ip6_tunnel tunnel6 tun binfmt_misc intel_rapl_msr intel_rapl_common rfkill kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel joydev virtio_balloon pcspkr i2c_piix4 sunrpc ip_tables xfs libcrc32c crc32c_intel serio_raw virtio_console ata_generic virtio_blk virtio_net net_failover failover ata_piix libata [ 171.199464] CPU: 1 PID: 5026 Comm: repro Not tainted 5.7.0-rc1.mptcp_f227fdf5d388+ #95 [ 171.200886] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014 [ 171.202546] RIP: 0010:warn_bad_map (linux-mptcp/net/mptcp/subflow.c:533 linux-mptcp/net/mptcp/subflow.c:531) [ 171.206537] Code: c1 ea 03 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 1d 8b 55 3c 44 89 e6 48 c7 c7 20 51 13 95 e8 37 8b 22 fe <0f> 0b 48 83 c4 08 5b 5d 41 5c c3 89 4c 24 04 e8 db d6 94 fe 8b 4c [ 171.220473] RSP: 0018:ffffc90000150560 EFLAGS: 00010282 [ 171.221639] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 171.223108] RDX: 0000000000000000 RSI: 0000000000000008 RDI: fffff5200002a09e [ 171.224388] RBP: ffff8880aa6e3c00 R08: 0000000000000001 R09: fffffbfff2ec9955 [ 171.225706] R10: ffffffff9764caa7 R11: fffffbfff2ec9954 R12: 0000000000007fca [ 171.227211] R13: ffff8881066f4a7f R14: ffff8880aa6e3c00 R15: 0000000000000020 [ 171.228460] FS: 00007f8623719740(0000) GS:ffff88810be00000(0000) knlGS:0000000000000000 [ 171.230065] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 171.231303] CR2: 00007ffdab190a50 CR3: 00000001038ea006 CR4: 0000000000160ee0 [ 171.232586] Call Trace: [ 171.233109] <IRQ> [ 171.233531] get_mapping_status (linux-mptcp/net/mptcp/subflow.c:691) [ 171.234371] mptcp_subflow_data_available (linux-mptcp/net/mptcp/subflow.c:736 linux-mptcp/net/mptcp/subflow.c:832) [ 171.238181] subflow_state_change (linux-mptcp/net/mptcp/subflow.c:1085 (discriminator 1)) [ 171.239066] tcp_fin (linux-mptcp/net/ipv4/tcp_input.c:4217) [ 171.240123] tcp_data_queue (linux-mptcp/./include/linux/compiler.h:199 linux-mptcp/net/ipv4/tcp_input.c:4822) [ 171.245083] tcp_rcv_established (linux-mptcp/./include/linux/skbuff.h:1785 linux-mptcp/./include/net/tcp.h:1774 linux-mptcp/./include/net/tcp.h:1847 linux-mptcp/net/ipv4/tcp_input.c:5238 linux-mptcp/net/ipv4/tcp_input.c:5730) [ 171.254089] tcp_v4_rcv (linux-mptcp/./include/linux/spinlock.h:393 linux-mptcp/net/ipv4/tcp_ipv4.c:2009) [ 171.258969] ip_protocol_deliver_rcu (linux-mptcp/net/ipv4/ip_input.c:204 (discriminator 1)) [ 171.260214] ip_local_deliver_finish (linux-mptcp/./include/linux/rcupdate.h:651 linux-mptcp/net/ipv4/ip_input.c:232) [ 171.261389] ip_local_deliver (linux-mptcp/./include/linux/netfilter.h:307 linux-mptcp/./include/linux/netfilter.h:301 linux-mptcp/net/ipv4/ip_input.c:252) [ 171.265884] ip_rcv (linux-mptcp/./include/linux/netfilter.h:307 linux-mptcp/./include/linux/netfilter.h:301 linux-mptcp/net/ipv4/ip_input.c:539) [ 171.273666] process_backlog (linux-mptcp/./include/linux/rcupdate.h:651 linux-mptcp/net/core/dev.c:6135) [ 171.275328] net_rx_action (linux-mptcp/net/core/dev.c:6572 linux-mptcp/net/core/dev.c:6640) [ 171.280472] __do_softirq (linux-mptcp/./arch/x86/include/asm/jump_label.h:25 linux-mptcp/./include/linux/jump_label.h:200 linux-mptcp/./include/trace/events/irq.h:142 linux-mptcp/kernel/softirq.c:293) [ 171.281379] do_softirq_own_stack (linux-mptcp/arch/x86/entry/entry_64.S:1083) [ 171.282358] </IRQ> We could address the issue clearing explicitly the relevant fields in several places - tcp_parse_option, tcp_fast_parse_options, possibly others. Instead we move the MPTCP option parsing into the already existing mptcp ingress hook, so that we need to clear the fields in a single place. This allows us dropping an MPTCP hook from the TCP code and removing the quite large mptcp_options_received from the tcp_sock struct. On the flip side, the MPTCP sockets will traverse the option space twice (in tcp_parse_option() and in mptcp_incoming_options(). That looks acceptable: we already do that for syn and 3rd ack packets, plain TCP socket will benefit from it, and even MPTCP sockets will experience better code locality, reducing the jumps between TCP and MPTCP code. v1 -> v2: - rebased on current '-net' tree Fixes: 648ef4b88673 ("mptcp: Implement MPTCP receive path") Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
The mptcp_options_received structure carries several per
packet flags (mp_capable, mp_join, etc.). Such fields must
be cleared on each packet, even on dropped ones or packet
not carrying any MPTCP options, but the current mptcp
code clears them only on TCP option reset.

On several races/corner cases we end-up with stray bits in
incoming options, leading to WARN_ON splats. e.g.:

[  171.164906] Bad mapping: ssn=32714 map_seq=1 map_data_len=32713
[  171.165006] WARNING: CPU: 1 PID: 5026 at net/mptcp/subflow.c:533 warn_bad_map (linux-mptcp/net/mptcp/subflow.c:533 linux-mptcp/net/mptcp/subflow.c:531)
[  171.167632] Modules linked in: ip6_vti ip_vti ip_gre ipip sit tunnel4 ip_tunnel geneve ip6_udp_tunnel udp_tunnel macsec macvtap tap ipvlan macvlan 8021q garp mrp xfrm_interface veth netdevsim nlmon dummy team bonding vcan bridge stp llc ip6_gre gre ip6_tunnel tunnel6 tun binfmt_misc intel_rapl_msr intel_rapl_common rfkill kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel joydev virtio_balloon pcspkr i2c_piix4 sunrpc ip_tables xfs libcrc32c crc32c_intel serio_raw virtio_console ata_generic virtio_blk virtio_net net_failover failover ata_piix libata
[  171.199464] CPU: 1 PID: 5026 Comm: repro Not tainted 5.7.0-rc1.mptcp_f227fdf5d388+ #95
[  171.200886] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
[  171.202546] RIP: 0010:warn_bad_map (linux-mptcp/net/mptcp/subflow.c:533 linux-mptcp/net/mptcp/subflow.c:531)
[  171.206537] Code: c1 ea 03 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 1d 8b 55 3c 44 89 e6 48 c7 c7 20 51 13 95 e8 37 8b 22 fe <0f> 0b 48 83 c4 08 5b 5d 41 5c c3 89 4c 24 04 e8 db d6 94 fe 8b 4c
[  171.220473] RSP: 0018:ffffc90000150560 EFLAGS: 00010282
[  171.221639] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[  171.223108] RDX: 0000000000000000 RSI: 0000000000000008 RDI: fffff5200002a09e
[  171.224388] RBP: ffff8880aa6e3c00 R08: 0000000000000001 R09: fffffbfff2ec9955
[  171.225706] R10: ffffffff9764caa7 R11: fffffbfff2ec9954 R12: 0000000000007fca
[  171.227211] R13: ffff8881066f4a7f R14: ffff8880aa6e3c00 R15: 0000000000000020
[  171.228460] FS:  00007f8623719740(0000) GS:ffff88810be00000(0000) knlGS:0000000000000000
[  171.230065] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  171.231303] CR2: 00007ffdab190a50 CR3: 00000001038ea006 CR4: 0000000000160ee0
[  171.232586] Call Trace:
[  171.233109]  <IRQ>
[  171.233531] get_mapping_status (linux-mptcp/net/mptcp/subflow.c:691)
[  171.234371] mptcp_subflow_data_available (linux-mptcp/net/mptcp/subflow.c:736 linux-mptcp/net/mptcp/subflow.c:832)
[  171.238181] subflow_state_change (linux-mptcp/net/mptcp/subflow.c:1085 (discriminator 1))
[  171.239066] tcp_fin (linux-mptcp/net/ipv4/tcp_input.c:4217)
[  171.240123] tcp_data_queue (linux-mptcp/./include/linux/compiler.h:199 linux-mptcp/net/ipv4/tcp_input.c:4822)
[  171.245083] tcp_rcv_established (linux-mptcp/./include/linux/skbuff.h:1785 linux-mptcp/./include/net/tcp.h:1774 linux-mptcp/./include/net/tcp.h:1847 linux-mptcp/net/ipv4/tcp_input.c:5238 linux-mptcp/net/ipv4/tcp_input.c:5730)
[  171.254089] tcp_v4_rcv (linux-mptcp/./include/linux/spinlock.h:393 linux-mptcp/net/ipv4/tcp_ipv4.c:2009)
[  171.258969] ip_protocol_deliver_rcu (linux-mptcp/net/ipv4/ip_input.c:204 (discriminator 1))
[  171.260214] ip_local_deliver_finish (linux-mptcp/./include/linux/rcupdate.h:651 linux-mptcp/net/ipv4/ip_input.c:232)
[  171.261389] ip_local_deliver (linux-mptcp/./include/linux/netfilter.h:307 linux-mptcp/./include/linux/netfilter.h:301 linux-mptcp/net/ipv4/ip_input.c:252)
[  171.265884] ip_rcv (linux-mptcp/./include/linux/netfilter.h:307 linux-mptcp/./include/linux/netfilter.h:301 linux-mptcp/net/ipv4/ip_input.c:539)
[  171.273666] process_backlog (linux-mptcp/./include/linux/rcupdate.h:651 linux-mptcp/net/core/dev.c:6135)
[  171.275328] net_rx_action (linux-mptcp/net/core/dev.c:6572 linux-mptcp/net/core/dev.c:6640)
[  171.280472] __do_softirq (linux-mptcp/./arch/x86/include/asm/jump_label.h:25 linux-mptcp/./include/linux/jump_label.h:200 linux-mptcp/./include/trace/events/irq.h:142 linux-mptcp/kernel/softirq.c:293)
[  171.281379] do_softirq_own_stack (linux-mptcp/arch/x86/entry/entry_64.S:1083)
[  171.282358]  </IRQ>

We could address the issue clearing explicitly the relevant fields
in several places - tcp_parse_option, tcp_fast_parse_options,
possibly others.

Instead we move the MPTCP option parsing into the already existing
mptcp ingress hook, so that we need to clear the fields in a single
place.

This allows us dropping an MPTCP hook from the TCP code and
removing the quite large mptcp_options_received from the tcp_sock
struct. On the flip side, the MPTCP sockets will traverse the
option space twice (in tcp_parse_option() and in
mptcp_incoming_options(). That looks acceptable: we already
do that for syn and 3rd ack packets, plain TCP socket will
benefit from it, and even MPTCP sockets will experience better
code locality, reducing the jumps between TCP and MPTCP code.

v1 -> v2:
 - rebased on current '-net' tree

Fixes: 648ef4b88673 ("mptcp: Implement MPTCP receive path")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
mptcp: consolidate synack processing. 2020-04-30T19:23:22+00:00 Paolo Abeni pabeni@redhat.com 2020-04-30T13:01:51+00:00 263e1201a2c324b60b15ecda5de9ebf1e7293e31 Currently the MPTCP code uses 2 hooks to process syn-ack packets, mptcp_rcv_synsent() and the sk_rx_dst_set() callback. We can drop the first, moving the relevant code into the latter, reducing the hooking into the TCP code. This is also needed by the next patch. v1 -> v2: - use local tcp sock ptr instead of casting the sk variable several times - DaveM Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
Currently the MPTCP code uses 2 hooks to process syn-ack
packets, mptcp_rcv_synsent() and the sk_rx_dst_set()
callback.

We can drop the first, moving the relevant code into the
latter, reducing the hooking into the TCP code. This is
also needed by the next patch.

v1 -> v2:
 - use local tcp sock ptr instead of casting the sk variable
   several times - DaveM

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
inet: Use fallthrough; 2020-03-12T22:55:00+00:00 Joe Perches joe@perches.com 2020-03-12T22:50:22+00:00 a8eceea84a3a3504e42f6495cf462027c5d19cb0 Convert the various uses of fallthrough comments to fallthrough; Done via script Link: https://lore.kernel.org/lkml/b56602fcf79f849e733e7b521bb0e17895d390fa.1582230379.git.joe@perches.com/ And by hand: net/ipv6/ip6_fib.c has a fallthrough comment outside of an #ifdef block that causes gcc to emit a warning if converted in-place. So move the new fallthrough; inside the containing #ifdef/#endif too. Signed-off-by: Joe Perches <joe@perches.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
Convert the various uses of fallthrough comments to fallthrough;

Done via script
Link: https://lore.kernel.org/lkml/b56602fcf79f849e733e7b521bb0e17895d390fa.1582230379.git.joe@perches.com/

And by hand:

net/ipv6/ip6_fib.c has a fallthrough comment outside of an #ifdef block
that causes gcc to emit a warning if converted in-place.

So move the new fallthrough; inside the containing #ifdef/#endif too.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
tcp: fix TFO SYNACK undo to avoid double-timestamp-undo 2020-02-24T01:23:35+00:00 Neal Cardwell ncardwell@google.com 2020-02-22T16:21:15+00:00 dad8cea7add96a353fa1898b5ccefbb72da66f29 In a rare corner case the new logic for undo of SYNACK RTO could result in triggering the warning in tcp_fastretrans_alert() that says: WARN_ON(tp->retrans_out != 0); The warning looked like: WARNING: CPU: 1 PID: 1 at net/ipv4/tcp_input.c:2818 tcp_ack+0x13e0/0x3270 The sequence that tickles this bug is: - Fast Open server receives TFO SYN with data, sends SYNACK - (client receives SYNACK and sends ACK, but ACK is lost) - server app sends some data packets - (N of the first data packets are lost) - server receives client ACK that has a TS ECR matching first SYNACK, and also SACKs suggesting the first N data packets were lost - server performs TS undo of SYNACK RTO, then immediately enters recovery - buggy behavior then performed a *second* undo that caused the connection to be in CA_Open with retrans_out != 0 Basically, the incoming ACK packet with SACK blocks causes us to first undo the cwnd reduction from the SYNACK RTO, but then immediately enters fast recovery, which then makes us eligible for undo again. And then tcp_rcv_synrecv_state_fastopen() accidentally performs an undo using a "mash-up" of state from two different loss recovery phases: it uses the timestamp info from the ACK of the original SYNACK, and the undo_marker from the fast recovery. This fix refines the logic to only invoke the tcp_try_undo_loss() inside tcp_rcv_synrecv_state_fastopen() if the connection is still in CA_Loss. If peer SACKs triggered fast recovery, then tcp_rcv_synrecv_state_fastopen() can't safely undo. Fixes: 794200d66273 ("tcp: undo cwnd on Fast Open spurious SYNACK retransmit") Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
In a rare corner case the new logic for undo of SYNACK RTO could
result in triggering the warning in tcp_fastretrans_alert() that says:
        WARN_ON(tp->retrans_out != 0);

The warning looked like:

WARNING: CPU: 1 PID: 1 at net/ipv4/tcp_input.c:2818 tcp_ack+0x13e0/0x3270

The sequence that tickles this bug is:
 - Fast Open server receives TFO SYN with data, sends SYNACK
 - (client receives SYNACK and sends ACK, but ACK is lost)
 - server app sends some data packets
 - (N of the first data packets are lost)
 - server receives client ACK that has a TS ECR matching first SYNACK,
   and also SACKs suggesting the first N data packets were lost
    - server performs TS undo of SYNACK RTO, then immediately
      enters recovery
    - buggy behavior then performed a *second* undo that caused
      the connection to be in CA_Open with retrans_out != 0

Basically, the incoming ACK packet with SACK blocks causes us to first
undo the cwnd reduction from the SYNACK RTO, but then immediately
enters fast recovery, which then makes us eligible for undo again. And
then tcp_rcv_synrecv_state_fastopen() accidentally performs an undo
using a "mash-up" of state from two different loss recovery phases: it
uses the timestamp info from the ACK of the original SYNACK, and the
undo_marker from the fast recovery.

This fix refines the logic to only invoke the tcp_try_undo_loss()
inside tcp_rcv_synrecv_state_fastopen() if the connection is still in
CA_Loss.  If peer SACKs triggered fast recovery, then
tcp_rcv_synrecv_state_fastopen() can't safely undo.

Fixes: 794200d66273 ("tcp: undo cwnd on Fast Open spurious SYNACK retransmit")
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>