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Thu, 02 Apr 2026 02:46:46 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 2 Apr 2026 11:46:44 +0200 To: Kumar Kartikeya Dwivedi Cc: Varun R Mallya , bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, yonghong.song@linux.dev, rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Message-ID: References: <20260401191126.440683-1-varunrmallya@gmail.com> <20260401191126.440683-2-varunrmallya@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=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Apr 02, 2026 at 12:50:10AM +0200, Kumar Kartikeya Dwivedi wrote: > On Wed, 1 Apr 2026 at 21:11, Varun R Mallya wrote: > > > > Add a selftest to ensure that kprobe_multi programs cannot be attached > > using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel > > rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set. > > > > Signed-off-by: Varun R Mallya > > --- > > Acked-by: Kumar Kartikeya Dwivedi > > > .../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++ > > .../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++ > > 2 files changed, 54 insertions(+) > > create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c > > > > diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c > > index 78c974d4ea33..f02fec2b6fda 100644 > > --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c > > +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c > > @@ -10,6 +10,7 @@ > > #include "kprobe_multi_session_cookie.skel.h" > > #include "kprobe_multi_verifier.skel.h" > > #include "kprobe_write_ctx.skel.h" > > +#include "kprobe_multi_sleepable.skel.h" > > #include "bpf/libbpf_internal.h" > > #include "bpf/hashmap.h" > > > > @@ -633,6 +634,44 @@ static void test_attach_write_ctx(void) > > } > > #endif > > > > +static void test_attach_multi_sleepable(void) > > +{ > > + struct kprobe_multi_sleepable *skel; > > + int err; > > + > > + skel = kprobe_multi_sleepable__open(); > > + if (!ASSERT_OK_PTR(skel, "kprobe_multi_sleepable__open")) > > + return; > > + > > + err = bpf_program__set_flags(skel->progs.handle_kprobe_multi_sleepable, > > + BPF_F_SLEEPABLE); > > + if (!ASSERT_OK(err, "bpf_program__set_flags")) > > + goto cleanup; > > + > > + /* Load should succeed even with BPF_F_SLEEPABLE for KPROBE types */ > > + err = kprobe_multi_sleepable__load(skel); > > + if (!ASSERT_OK(err, "kprobe_multi_sleepable__load")) > > + goto cleanup; > > + > > + /* Attachment must fail for kprobe.multi + BPF_F_SLEEPABLE. > > + * Also chosen a stable symbol to send into opts > > + */ > > + LIBBPF_OPTS(bpf_kprobe_multi_opts, opts); > > + const char *sym = "vfs_read"; > > + > > + opts.syms = &sym; > > + opts.cnt = 1; > > + > > + skel->links.handle_kprobe_multi_sleepable = > > + bpf_program__attach_kprobe_multi_opts(skel->progs.handle_kprobe_multi_sleepable, > > + NULL, &opts); > > + ASSERT_ERR_PTR(skel->links.handle_kprobe_multi_sleepable, > > + "bpf_program__attach_kprobe_multi_opts"); > > Nit: While vfs_read will likely remain stable, the check could > probably be stronger to distinguish an attach error from -EINVAL? > I added a typo to vfs_read and it still passed, because it failed to > attach instead of getting rejected on unfixed kernel. > May not be a big deal since vfs_read is unlikely to break. > I verified it works by adding bpf_copy_from_user to the program and > attaching to SYS_PREFIX sys_getpid and invoking the splat though, so > LGTM otherwise. why not use bpf_fentry_test2 ? you could also put it in pattern argument and bypass opts completely (up to you) also there's test_attach_api_fails test, please move it over there thanks, jirka