Re: [PATCH v3 1/3] bpf: propagate cb_access from freplace programs

[Alexei Starovoitov]

On Mon, Sep 21, 2026 at 12:32 AM Weiming Shi <bestswngs@xxxxxxxxx> wrote:
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: be8704ff07d2 ("bpf: Introduce dynamic program extensions")

That shouldn't go to stable. Loading an EXT prog takes CAP_BPF +
CAP_NET_ADMIN + CAP_PERFMON.

[...]

> +	if (prog->type == BPF_PROG_TYPE_EXT && READ_ONCE(prog->cb_access)) {
> +		WRITE_ONCE(tgt_prog->cb_access, true);
> +		/* Drain runs that observed cb_access=false before enabling freplace. */
> +		synchronize_rcu();
> +	}

tc doesn't look at cb_access at all, yet every tc freplace that touches
cb[] now waits for an RCU grace period in attach.

This is a separate issue from the LWT one. Patch 2 resets the cb after
the run whether the prog has cb_access or not, so it doesn't depend on
this patch. Pls drop it from this series.