netdev - [PATCH bpf-next] selftests/bpf: Switch test_vmlinux to use hrtimer_range_start

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Date:   Tue, 30 Jun 2020 11:49:22 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-kselftest@...r.kernel.org
Cc:     sdf@...gle.com, Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Hao Luo <haoluo@...gle.com>
Subject: [PATCH bpf-next] selftests/bpf: Switch test_vmlinux to use hrtimer_range_start_ns.

The test_vmlinux test uses hrtimer_nanosleep as hook to test tracing
programs. But it seems Clang may have done an aggressive optimization,
causing fentry and kprobe to not hook on this function properly on a
Clang build kernel.

A possible fix is switching to use a more reliable function, e.g. the
ones exported to kernel modules such as hrtimer_range_start_ns. After
we switch to using hrtimer_range_start_ns, the test passes again even
on a clang build kernel.

Tested:
 In a clang build kernel, the test fail even when the flags
 {fentry, kprobe}_called are set unconditionally in handle__kprobe()
 and handle__fentry(), which implies the programs do not hook on
 hrtimer_nanosleep() properly. This could be because clang's code
 transformation is too aggressive.

 test_vmlinux:PASS:skel_open 0 nsec
 test_vmlinux:PASS:skel_attach 0 nsec
 test_vmlinux:PASS:tp 0 nsec
 test_vmlinux:PASS:raw_tp 0 nsec
 test_vmlinux:PASS:tp_btf 0 nsec
 test_vmlinux:FAIL:kprobe not called
 test_vmlinux:FAIL:fentry not called

 After we switch to hrtimer_range_start_ns, the test passes.

 test_vmlinux:PASS:skel_open 0 nsec
 test_vmlinux:PASS:skel_attach 0 nsec
 test_vmlinux:PASS:tp 0 nsec
 test_vmlinux:PASS:raw_tp 0 nsec
 test_vmlinux:PASS:tp_btf 0 nsec
 test_vmlinux:PASS:kprobe 0 nsec
 test_vmlinux:PASS:fentry 0 nsec

Signed-off-by: Hao Luo <haoluo@...gle.com>
---
 tools/testing/selftests/bpf/progs/test_vmlinux.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_vmlinux.c b/tools/testing/selftests/bpf/progs/test_vmlinux.c
index 5611b564d3b1..29fa09d6a6c6 100644
--- a/tools/testing/selftests/bpf/progs/test_vmlinux.c
+++ b/tools/testing/selftests/bpf/progs/test_vmlinux.c
@@ -63,20 +63,20 @@ int BPF_PROG(handle__tp_btf, struct pt_regs *regs, long id)
 	return 0;
 }
 
-SEC("kprobe/hrtimer_nanosleep")
-int BPF_KPROBE(handle__kprobe,
-	       ktime_t rqtp, enum hrtimer_mode mode, clockid_t clockid)
+SEC("kprobe/hrtimer_start_range_ns")
+int BPF_KPROBE(handle__kprobe, struct hrtimer *timer, ktime_t tim, u64 delta_ns,
+	       const enum hrtimer_mode mode)
 {
-	if (rqtp == MY_TV_NSEC)
+	if (tim == MY_TV_NSEC)
 		kprobe_called = true;
 	return 0;
 }
 
-SEC("fentry/hrtimer_nanosleep")
-int BPF_PROG(handle__fentry,
-	     ktime_t rqtp, enum hrtimer_mode mode, clockid_t clockid)
+SEC("fentry/hrtimer_start_range_ns")
+int BPF_PROG(handle__fentry, struct hrtimer *timer, ktime_t tim, u64 delta_ns,
+	     const enum hrtimer_mode mode)
 {
-	if (rqtp == MY_TV_NSEC)
+	if (tim == MY_TV_NSEC)
 		fentry_called = true;
 	return 0;
 }
-- 
2.27.0.212.ge8ba1cc988-goog