lkml.org 
[lkml]   [2020]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH bpf-next] selftests/bpf: Switch test_vmlinux to use hrtimer_range_start_ns.
On Tue, Jun 30, 2020 at 1:47 PM Hao Luo <haoluo@google.com> wrote:
>
> 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@google.com>
> ---

Took me a bit of jumping around to find how it is related to nanosleep
call :) But seems like it's unconditionally called, so should be fine.

Acked-by: Andrii Nakryiko <andriin@fb.com>


> tools/testing/selftests/bpf/progs/test_vmlinux.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>

[...]

\
 
 \ /
  Last update: 2020-06-30 23:26    [W:0.067 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site