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[2a01:cb08:8949:7e00:f765:9600:8310:132d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e702ec426sm169695515e9.10.2026.05.11.03.19.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 May 2026 03:19:49 -0700 (PDT) Date: Mon, 11 May 2026 12:19:47 +0200 From: Paul Chaignon To: Alexei Starovoitov Cc: Eduard Zingerman , bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Kumar Kartikeya Dwivedi Subject: Re: [PATCH bpf] bpf: Don't run arg-tracking analysis twice on main subprog Message-ID: References: <3e3a145bfb6c17535c5c921c60f405d56d32bf7d.camel@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Sat, May 09, 2026 at 04:16:10PM -0700, Alexei Starovoitov wrote: > On Sat, May 9, 2026 at 4:50 AM Eduard Zingerman wrote: > > > > On Fri, 2026-05-08 at 16:24 -0700, Alexei Starovoitov wrote: > > > On Thu, May 7, 2026 at 11:22 AM Paul Chaignon wrote: > > > > > > > > Because subprog 0, the main subprog, is considered a global function, > > > > we end up running the arg-tracking dataflow analysis twice on it. That > > > > results in slightly longer verification but mostly in more verbose > > > > verifier logs. This patch fixes it by keeping only the iteration over > > > > global subprogs. > > > > > > > > When running over all of Cilium's programs with BPF_LOG_LEVEL2, this > > > > reduces verbosity by ~20% on average. > > > > > > > > Fixes: bf0c571f7feb6 ("bpf: introduce forward arg-tracking dataflow analysis") > > > > Signed-off-by: Paul Chaignon > > > > --- > > > > kernel/bpf/liveness.c | 11 ++--------- > > > > 1 file changed, 2 insertions(+), 9 deletions(-) > > > > > > > > diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c > > > > index 332e6e003f27..505250998f36 100644 > > > > --- a/kernel/bpf/liveness.c > > > > +++ b/kernel/bpf/liveness.c > > > > @@ -1914,15 +1914,6 @@ int bpf_compute_subprog_arg_access(struct bpf_verifier_env *env) > > > > return -ENOMEM; > > > > } > > > > > > > > - instance = call_instance(env, NULL, 0, 0); > > > > - if (IS_ERR(instance)) { > > > > - err = PTR_ERR(instance); > > > > - goto out; > > > > - } > > > > - err = analyze_subprog(env, NULL, info, instance, callsites); > > > > - if (err) > > > > - goto out; > > > > - > > > > /* > > > > * Subprogs and callbacks that don't receive FP-derived arguments > > > > * cannot access ancestor stack frames, so they were skipped during > > > > @@ -1934,6 +1925,8 @@ int bpf_compute_subprog_arg_access(struct bpf_verifier_env *env) > > > > * each subprog is analyzed before its callees, allowing the > > > > * recursive walk inside analyze_subprog() to naturally > > > > * reach nested callees that also lack FP-derived args. > > > > + * > > > > + * Note the main subprog is also analyzed as part of this loop. > > > > */ > > > > > > Thanks for the report. > > > I guess the fix is correct. > > > This part of the comment needs to be adjusted: > > > "they were skipped during > > > * the recursive walk above." > > > > > > I wonder whether something like this is cleaner? > > > - if (info[sub].at_in && !bpf_subprog_is_global(env, sub)) > > > + if (info[sub].at_in && (!bpf_subprog_is_global(env, > > > sub) || sub == 0)) > > > > > > This part of the comment: > > > "Async callbacks (timer, workqueue) are > > > * also not reachable from the main program's call graph." > > > > > > is also not quite correct. > > > In here: > > > } else if (bpf_calls_callback(env, idx)) { > > > callee = find_callback_subprog(env, insn, idx, > > > &caller_reg, &cb_callee_reg); > > > > > > they could have been reached, but find_callback_subprog() > > > will ignore timers because FP-derived args won't be passed > > > into them. > > > > > > Eduard, > > > wdyt? > > > > This is a nice catch. Idk if 'sub == 0' part is necessary, tbh. > > Paul, please add my acked-by when you respin with fixed comments. > > > > Acked-by: Eduard Zingerman > > Reworded myself and applied. Thanks!