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

[Jiayuan Chen <jiayuan.chen@linux.dev>]

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