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([2804:5078:834:1300:58f2:fc97:371f:3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43b51892234sm15806000f8f.24.2026.03.19.07.35.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Mar 2026 07:35:21 -0700 (PDT) Message-ID: Subject: Re: [PATCH 3/8] selftests: livepatch: test-kprobe: Check if kprobes can work with livepatches From: Marcos Paulo de Souza To: Joe Lawrence Cc: Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Shuah Khan , live-patching@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 19 Mar 2026 11:35:16 -0300 In-Reply-To: References: <20260313-lp-tests-old-fixes-v1-0-71ac6dfb3253@suse.com> <20260313-lp-tests-old-fixes-v1-3-71ac6dfb3253@suse.com> Autocrypt: addr=mpdesouza@suse.com; prefer-encrypt=mutual; keydata=mDMEZ/0YqhYJKwYBBAHaRw8BAQdA4JZz0FED+JD5eKlhkNyjDrp6lAGmgR3LPTduPYGPT Km0Kk1hcmNvcyBQYXVsbyBkZSBTb3V6YSA8bXBkZXNvdXphQHN1c2UuY29tPoiTBBMWCgA7FiEE2g gC66iLbhUsCBoBemssEuRpLLUFAmf9GKoCGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk QemssEuRpLLWGxwD/S1I0bjp462FlKb81DikrOfWbeJ0FOJP44eRzmn20HmEBALBZIMrfIH2dJ5eM GO8seNG8sYiP6JfRjl7Hyqca6YsE Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (by Flathub.org) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2026-03-16 at 16:38 -0400, Joe Lawrence wrote: > On Fri, Mar 13, 2026 at 05:58:34PM -0300, Marcos Paulo de Souza > wrote: > > Running the upstream selftests on older kernels can presente some > > issues > > regarding features being not present. One of such issues if the > > missing > > capability of having both kprobes and livepatches on the same > > function. > >=20 >=20 > nit picking, but slightly reworded for clarity and spelling: >=20 > Running upstream selftests on older kernels can be problematic when > features or fixes from newer versions are not present. For example, > older kernels may lack the capability to support kprobes and > livepatches > on the same function simultaneously. Much better, I'll pick your description for v2. >=20 > > The support was introduced in commit 0bc11ed5ab60c > > ("kprobes: Allow kprobes coexist with livepatch"), which means that > > older > > kernels may lack this change. > >=20 > > The lack of this feature can be checked when a kprobe without a > > post_handler is loaded and checking that the enabled_function's > > file > > shows the flag "I". A kernel with the proper support for kprobes > > and > > livepatches would presente the flag only when a post_handler is >=20 > nit: s/presente/present Ok. >=20 > > registered. > >=20 > > No functional changes. > >=20 > > Signed-off-by: Marcos Paulo de Souza > > --- > > =C2=A0tools/testing/selftests/livepatch/test-kprobe.sh | 52 > > ++++++++++++++---------- > > =C2=A01 file changed, 31 insertions(+), 21 deletions(-) > >=20 > > diff --git a/tools/testing/selftests/livepatch/test-kprobe.sh > > b/tools/testing/selftests/livepatch/test-kprobe.sh > > index cdf31d0e51955..44cd16156dbd4 100755 > > --- a/tools/testing/selftests/livepatch/test-kprobe.sh > > +++ b/tools/testing/selftests/livepatch/test-kprobe.sh > > @@ -16,30 +16,19 @@ setup_config > > =C2=A0# when it uses a post_handler since only one IPMODIFY maybe be > > registered > > =C2=A0# to any given function at a time. > > =C2=A0 > > -start_test "livepatch interaction with kprobed function with > > post_handler" > > - > > -echo 1 > "$SYSFS_KPROBES_DIR/enabled" > > - > > -load_mod $MOD_KPROBE has_post_handler=3D1 > > -load_failing_mod $MOD_LIVEPATCH > > -unload_mod $MOD_KPROBE > > - > > -check_result "% insmod test_modules/test_klp_kprobe.ko > > has_post_handler=3D1 > > -% insmod test_modules/$MOD_LIVEPATCH.ko > > -livepatch: enabling patch '$MOD_LIVEPATCH' > > -livepatch: '$MOD_LIVEPATCH': initializing patching transition > > -livepatch: failed to register ftrace handler for function > > 'cmdline_proc_show' (-16) > > -livepatch: failed to patch object 'vmlinux' > > -livepatch: failed to enable patch '$MOD_LIVEPATCH' > > -livepatch: '$MOD_LIVEPATCH': canceling patching transition, going > > to unpatch > > -livepatch: '$MOD_LIVEPATCH': completing unpatching transition > > -livepatch: '$MOD_LIVEPATCH': unpatching complete > > -insmod: ERROR: could not insert module > > test_modules/$MOD_LIVEPATCH.ko: Device or resource busy > > -% rmmod test_klp_kprobe" > > - > > =C2=A0start_test "livepatch interaction with kprobed function without > > post_handler" > > =C2=A0 > > =C2=A0load_mod $MOD_KPROBE has_post_handler=3D0 > > + > > +# Check if commit 0bc11ed5ab60c ("kprobes: Allow kprobes coexist > > with livepatch") > > +# is missing, meaning that livepatches and kprobes can't be used > > together. > > +# When the commit is missing, kprobes always set IPMODIFY (the I > > flag), even > > +# when the post handler is missing. > > +if grep --quiet ") R I" > > "$SYSFS_DEBUG_DIR/tracing/enabled_functions"; then >=20 > Will flags R I always be in this order? seq_printf(m, " (%ld)%s%s%s%s%s", ftrace_rec_count(rec), rec->flags & FTRACE_FL_REGS ? " R" : " ", rec->flags & FTRACE_FL_IPMODIFY ? " I" : "=20 ", So this is safe. I'll add a comment in the patch to explain why this is safe too. Thanks for the comment! >=20 > -- > Joe