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Mon, 16 Mar 2026 10:23:58 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 16 Mar 2026 13:23:55 -0400 Message-Id: To: , Cc: , , , , , , , , , , Subject: Re: [PATCH bpf-next v6 1/2] bpf: Only enforce 8 frame call stack limit for all-static stacks From: "Emil Tsalapatis" X-Mailer: aerc 0.20.1 References: <20260316161225.128011-2-emil@etsalapatis.com> <65e11260b42493b1261ff79a8d2c408cdbe8a68038bea605e1794f75ff406594@mail.kernel.org> In-Reply-To: <65e11260b42493b1261ff79a8d2c408cdbe8a68038bea605e1794f75ff406594@mail.kernel.org> On Mon Mar 16, 2026 at 1:01 PM EDT, bot+bpf-ci wrote: >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index e29f15419fcb..01c18f4268de 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c > > [ ... ] > >> @@ -6854,7 +6854,16 @@ static int check_max_stack_depth_subprog(struct b= pf_verifier_env *env, int idx, > > [ ... ] > >> - frame++; >> + frame =3D subprog_is_global(env, idx) ? 0 : frame + 1; >> if (frame >=3D MAX_CALL_FRAMES) { >> verbose(env, "the call stack of %d frames is too deep !\n", >> frame); > > [ ... ] > >> diff --git a/tools/testing/selftests/bpf/progs/test_global_func3.c b/too= ls/testing/selftests/bpf/progs/test_global_func3.c >> index 142b682d3c2f..974fd8c19561 100644 >> --- a/tools/testing/selftests/bpf/progs/test_global_func3.c >> +++ b/tools/testing/selftests/bpf/progs/test_global_func3.c > > [ ... ] > >> SEC("tc") >> -__failure __msg("the call stack of 8 frames") >> +__failure __msg("the call stack of 9 frames") >> int global_func3(struct __sk_buff *skb) >> { >> return f8(skb); > > Should the expected message here be "the call stack of 8 frames" > rather than 9? > > The test has 9 functions total (global_func3 plus f1 through f8), > but only 8 call transitions, and frame starts at 0. Each static > call increments frame by one: > > frame =3D subprog_is_global(env, idx) ? 0 : frame + 1; > if (frame >=3D MAX_CALL_FRAMES) { > verbose(env, "the call stack of %d frames is too deep !\n", > frame); > > With 8 static calls (global_func3 -> f8 -> f7 -> ... -> f1), > frame reaches 8 which triggers the check since MAX_CALL_FRAMES > is 8. The verifier would print "the call stack of 8 frames is > too deep" and the __msg substring match for "9 frames" would not > match, causing the test to fail. > > The old test with global functions also had 8 call transitions > and expected "8 frames", since frame++ produced the same value > of 8 at the limit. > Same answer as in the previous version, the test passes fine.=20 > --- > 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/READM= E.md > > CI run summary: https://github.com/kernel-patches/bpf/actions/runs/231546= 16737