[PATCH bpf-next v4] bpf: drop duplicate check_app_limited in tcp_bpf_push

[PATCH bpf-next v4] bpf: drop duplicate check_app_limited in tcp_bpf_push

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

Commit c5c37af6ecad9 ("tcp: Convert do_tcp_sendpages() to use
MSG_SPLICE_PAGES") moved tcp_rate_check_app_limited() inside
do_tcp_sendpages(), turning it into a wrapper around tcp_sendmsg_locked().
Later, commit ebf2e8860eea ("tcp_bpf: Inline do_tcp_sendpages as it's now
a wrapper around tcp_sendmsg") inlined the wrapper in tcp_bpf_push() with
direct tcp_sendmsg_locked() calls, which perform the check on every path
that queues data, but kept the outer tcp_rate_check_app_limited() that
was previously needed to cover do_tcp_sendpages(). The outer call is now
redundant.

The site changed here, tcp_bpf_push(), holds the socket lock and invokes
tcp_sendmsg_locked() on every iteration. The early-return paths in
tcp_sendmsg_locked() that skip tcp_rate_check_app_limited() - the
MSG_ZEROCOPY allocation failure and MSG_FASTOPEN branches - return without
queueing any MSG_SPLICE_PAGES data, so there is no functional consequence
from omitting the outer check.

A potential benefit of this change is that it facilitates future reuse of
tcp_bpf_push() for sockmap support in protocols beyond TCP, such as MPTCP.
Since tcp_rate_check_app_limited() is TCP-specific while sendmsg_locked()
is a generic interface in struct proto_ops, this change allows us to switch
to different protocols via sk->sk_socket->ops->sendmsg_locked() without
carrying protocol-specific assumptions.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
Note:

This patch was originally part of my ongoing "MPTCP sockmap support"
series [1] (patch 5). Matthieu suggested converting it to a fix and sending
it directly to netdev. Removing the redundant tcp_rate_check_app_limited()
call benefits my subsequent MPTCP work: in patch 3 of that series, I
implement an MPTCP-specific mptcp_rate_check_app_limited() function and 
call it in mptcp_sendmsg_locked(). This allows me to reuse tcp_bpf_push()
by simply replacing tcp_sendmsg_locked() with

                sk->sk_socket->ops->sendmsg_locked(),

without carrying protocol-specific assumptions.

v4:
 - update the commit log as bot+bpf-ci suggested, cite ebf2e8860eea to
   clarify the inline history.

v3:
 - send this patch separately to bpf as Jakub suggested.
 - update the commit log as bot+bpf-ci suggested.
 - https://patchwork.kernel.org/project/netdevbpf/patch/85d9a0f138fa024354edde023a05f9d07b6ac87a.1789633546.git.tanggeliang@kylinos.cn/

v2:
 - drop the "Fixes" tags and update the prefixes and commit logs as Jiayuan
   suggested.
 - https://patchwork.kernel.org/project/netdevbpf/cover/cover.1789469930.git.tanggeliang@kylinos.cn/

v1:
 - https://patchwork.kernel.org/project/netdevbpf/cover/cover.1789368148.git.tanggeliang@kylinos.cn/

[1]
MPTCP sockmap support
https://lore.kernel.org/mptcp/b5f9e8d7-b738-1df6-3b5e-1d54cbbc663c@gmail.com/T/#t
---
 net/ipv4/tcp_bpf.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 2e234d155b5e..d5fcf3ce4861 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -108,7 +108,6 @@ static int tcp_bpf_push(struct sock *sk, struct sk_msg *msg, u32 apply_bytes,
 		off  = sge->offset;
 		page = sg_page(sge);
 
-		tcp_rate_check_app_limited(sk);
 retry:
 		msghdr.msg_flags = flags | MSG_SPLICE_PAGES;
 		has_tx_ulp = tls_sw_has_ctx_tx(sk);
-- 
2.53.0

Re: [PATCH bpf-next v4] bpf: drop duplicate check_app_limited in tcp_bpf_push

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 651 bytes --]

> bpf: drop duplicate check_app_limited in tcp_bpf_push

This isn't a bug, but would "bpf, sockmap: drop redundant
tcp_rate_check_app_limited() in tcp_bpf_push()" match the prefix and
naming used by the other changes to this file? The prefix for this file
is normally "bpf, sockmap:" (or "tcp_bpf:"), and "check_app_limited" is
not an identifier that exists - the removed call is
tcp_rate_check_app_limited().


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/35720598036

Re: [PATCH bpf-next v4] bpf: drop duplicate check_app_limited in tcp_bpf_push

[Jiayuan Chen]

On 9/22/26 7:06 PM, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
>
> Commit c5c37af6ecad9 ("tcp: Convert do_tcp_sendpages() to use
> MSG_SPLICE_PAGES") moved tcp_rate_check_app_limited() inside
> do_tcp_sendpages(), turning it into a wrapper around tcp_sendmsg_locked().
> Later, commit ebf2e8860eea ("tcp_bpf: Inline do_tcp_sendpages as it's now
> a wrapper around tcp_sendmsg") inlined the wrapper in tcp_bpf_push() with
> direct tcp_sendmsg_locked() calls, which perform the check on every path
> that queues data, but kept the outer tcp_rate_check_app_limited() that
> was previously needed to cover do_tcp_sendpages(). The outer call is now
> redundant.
>
> The site changed here, tcp_bpf_push(), holds the socket lock and invokes
> tcp_sendmsg_locked() on every iteration. The early-return paths in
> tcp_sendmsg_locked() that skip tcp_rate_check_app_limited() - the
> MSG_ZEROCOPY allocation failure and MSG_FASTOPEN branches - return without
> queueing any MSG_SPLICE_PAGES data, so there is no functional consequence
> from omitting the outer check.
>
> A potential benefit of this change is that it facilitates future reuse of
> tcp_bpf_push() for sockmap support in protocols beyond TCP, such as MPTCP.
> Since tcp_rate_check_app_limited() is TCP-specific while sendmsg_locked()
> is a generic interface in struct proto_ops, this change allows us to switch
> to different protocols via sk->sk_socket->ops->sendmsg_locked() without
> carrying protocol-specific assumptions.
>
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>


Thanks

Re: [PATCH bpf-next v4] bpf: drop duplicate check_app_limited in tcp_bpf_push

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Tue, 22 Sep 2026 19:06:18 +0800 you wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> Commit c5c37af6ecad9 ("tcp: Convert do_tcp_sendpages() to use
> MSG_SPLICE_PAGES") moved tcp_rate_check_app_limited() inside
> do_tcp_sendpages(), turning it into a wrapper around tcp_sendmsg_locked().
> Later, commit ebf2e8860eea ("tcp_bpf: Inline do_tcp_sendpages as it's now
> a wrapper around tcp_sendmsg") inlined the wrapper in tcp_bpf_push() with
> direct tcp_sendmsg_locked() calls, which perform the check on every path
> that queues data, but kept the outer tcp_rate_check_app_limited() that
> was previously needed to cover do_tcp_sendpages(). The outer call is now
> redundant.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v4] bpf: drop duplicate check_app_limited in tcp_bpf_push
    https://git.kernel.org/bpf/bpf-next/c/91f8613d95ad

You are awesome, thank you!
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