linux.git/net/ipv4/tcp_input.c, branch v6.15

Revert "tcp: avoid atomic operations on sk->sk_rmem_alloc"

2025-03-31T23:53:54+00:00

This reverts commit 0de2a5c4b824da2205658ebebb99a55c43cdf60f.

I forgot that a TCP socket could receive messages in its error queue.

sock_queue_err_skb() can be called without socket lock being held,
and changes sk->sk_rmem_alloc.

The fact that skbs in error queue are limited by sk->sk_rcvbuf
means that error messages can be dropped if socket receive
queues are full, which is an orthogonal issue.

In future kernels, we could use a separate sk->sk_error_mem_alloc
counter specifically for the error queue.

Fixes: 0de2a5c4b824 ("tcp: avoid atomic operations on sk->sk_rmem_alloc")
Signed-off-by: Eric Dumazet 
Link: https://patch.msgid.link/20250331075946.31960-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: avoid atomic operations on sk->sk_rmem_alloc

2025-03-25T14:37:16+00:00

TCP uses generic skb_set_owner_r() and sock_rfree()
for received packets, with socket lock being owned.

Switch to private versions, avoiding two atomic operations
per packet.

Signed-off-by: Eric Dumazet 
Reviewed-by: Neal Cardwell 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250320121604.3342831-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: move icsk_clean_acked to a better location

2025-03-24T16:55:18+00:00

As a followup of my presentation in Zagreb for netdev 0x19:

icsk_clean_acked is only used by TCP when/if CONFIG_TLS_DEVICE
is enabled from tcp_ack().

Rename it to tcp_clean_acked, move it to tcp_sock structure
in the tcp_sock_read_rx for better cache locality in TCP
fast path.

Define this field only when CONFIG_TLS_DEVICE is enabled
saving 8 bytes on configs not using it.

Signed-off-by: Eric Dumazet 
Reviewed-by: Neal Cardwell 
Reviewed-by: Sabrina Dubroca 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250317085313.2023214-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: cache RTAX_QUICKACK metric in a hot cache line

2025-03-18T12:44:59+00:00

tcp_in_quickack_mode() is called from input path for small packets.

It calls __sk_dst_get() which reads sk->sk_dst_cache which has been
put in sock_read_tx group (for good reasons).

Then dst_metric(dst, RTAX_QUICKACK) also needs extra cache line misses.

Cache RTAX_QUICKACK in icsk->icsk_ack.dst_quick_ack to no longer pull
these cache lines for the cases a delayed ACK is scheduled.

After this patch TCP receive path does not longer access sock_read_tx
group.

Signed-off-by: Eric Dumazet 
Reviewed-by: Jason Xing 
Reviewed-by: Neal Cardwell 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250312083907.1931644-1-edumazet@google.com
Signed-off-by: Paolo Abeni

tcp: helpers for ECN mode handling

2025-03-17T13:54:11+00:00

Create helpers for TCP ECN modes. No functional changes.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: Chia-Yu Chang 
Reviewed-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: rework {__,}tcp_ecn_check_ce() -> tcp_data_ecn_check()

2025-03-17T13:50:13+00:00

Rename tcp_ecn_check_ce to tcp_data_ecn_check as it is
called only for data segments, not for ACKs (with AccECN,
also ACKs may get ECN bits).

The extra "layer" in tcp_ecn_check_ce() function just
checks for ECN being enabled, that can be moved into
tcp_ecn_field_check rather than having the __ variant.

No functional changes.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: Chia-Yu Chang 
Reviewed-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: create FLAG_TS_PROGRESS

2025-03-17T13:48:39+00:00

Whenever timestamp advances, it declares progress which
can be used by the other parts of the stack to decide that
the ACK is the most recent one seen so far.

AccECN will use this flag when deciding whether to use the
ACK to update AccECN state or not.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: Chia-Yu Chang 
Reviewed-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: reorganize tcp_in_ack_event() and tcp_count_delivered()

2025-03-17T13:48:15+00:00

- Move tcp_count_delivered() earlier and split tcp_count_delivered_ce()
  out of it
- Move tcp_in_ack_event() later
- While at it, remove the inline from tcp_in_ack_event() and let
  the compiler to decide

Accurate ECN's heuristics does not know if there is going
to be ACE field based CE counter increase or not until after
rtx queue has been processed. Only then the number of ACKed
bytes/pkts is available. As CE or not affects presence of
FLAG_ECE, that information for tcp_in_ack_event is not yet
available in the old location of the call to tcp_in_ack_event().

Signed-off-by: Ilpo Järvinen 
Signed-off-by: Chia-Yu Chang 
Signed-off-by: David S. Miller

tcp: add a drop_reason pointer to tcp_check_req()

2025-03-03T23:44:19+00:00

We want to add new drop reasons for packets dropped in 3WHS in the
following patches.

tcp_rcv_state_process() has to set reason to TCP_FASTOPEN,
because tcp_check_req() will conditionally overwrite the drop_reason.

Signed-off-by: Eric Dumazet 
Reviewed-by: Jason Xing 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250301201424.2046477-2-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: be less liberal in TSEcr received while in SYN_RECV state

2025-02-27T02:11:17+00:00

Yong-Hao Zou mentioned that linux was not strict as other OS in 3WHS,
for flows using TCP TS option (RFC 7323)

As hinted by an old comment in tcp_check_req(),
we can check the TSEcr value in the incoming packet corresponds
to one of the SYNACK TSval values we have sent.

In this patch, I record the oldest and most recent values
that SYNACK packets have used.

Send a challenge ACK if we receive a TSEcr outside
of this range, and increase a new SNMP counter.

nstat -az | grep TSEcrRejected
TcpExtTSEcrRejected            0                  0.0

Due to TCP fastopen implementation, do not apply yet these checks
for fastopen flows.

v2: No longer use req->num_timeout, but treq->snt_tsval_first
    to detect when first SYNACK is prepared. This means
    we make sure to not send an initial zero TSval.
    Make sure MPTCP and TCP selftests are passing.
    Change MIB name to TcpExtTSEcrRejected

v1: https://lore.kernel.org/netdev/CADVnQykD8i4ArpSZaPKaoNxLJ2if2ts9m4As+=Jvdkrgx1qMHw@mail.gmail.com/T/

Reported-by: Yong-Hao Zou 
Signed-off-by: Eric Dumazet 
Reviewed-by: Matthieu Baerts (NGI0) 
Reviewed-by: Neal Cardwell 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250225171048.3105061-1-edumazet@google.com
Signed-off-by: Jakub Kicinski