linux-kernel - Re: [PATCH bpf-next v2] selftests/bpf: Switch test_vmlinux to use hrtimer_range_start

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Date:   Wed, 1 Jul 2020 11:04:12 -0700
From:   Yonghong Song <yhs@...com>
To:     Hao Luo <haoluo@...gle.com>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <clang-built-linux@...glegroups.com>
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>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2] selftests/bpf: Switch test_vmlinux to use
 hrtimer_range_start_ns.



On 7/1/20 10:53 AM, Hao Luo wrote:
> The test_vmlinux test uses hrtimer_nanosleep as hook to test tracing
> programs. But in a kernel built by clang, which performs more aggresive
> inlining, that function gets inlined into its caller SyS_nanosleep.
> Therefore, even though fentry and kprobe do hook on the function,
> they aren't triggered by the call to nanosleep in the test.
> 
> A possible fix is switching to use a function that is less likely to
> be inlined, such as hrtimer_range_start_ns. The EXPORT_SYMBOL functions
> shouldn't be inlined based on the description of [1], therefore safe
> to use for this test. Also the arguments of this function include the
> duration of sleep, therefore suitable for test verification.
> 
> [1] af3b56289be1 time: don't inline EXPORT_SYMBOL functions
> 
> Tested:
>   In a clang build kernel, before this change, the test fails:
> 
>   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 switching 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>
> Acked-by: Andrii Nakryiko <andriin@...com>

Thanks!
Acked-by: Yonghong Song <yhs@...com>