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SubjectRe: [PATCH] selftests/ftrace: Extend multiple_kprobes.tc to add multiple consecutive probes in a function
Masami Hiramatsu wrote:
> On Thu, 12 Jan 2023 18:51:14 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>
>> Akanksha J N wrote:
>> > Commit 97f88a3d723162 ("powerpc/kprobes: Fix null pointer reference in
>> > arch_prepare_kprobe()") fixed a recent kernel oops that was caused as
>> > ftrace-based kprobe does not generate kprobe::ainsn::insn and it gets
>> > set to NULL.
>> > Extend multiple kprobes test to add kprobes on first 256 bytes within a
>> > function, to be able to test potential issues with kprobes on
>> > successive instructions.
>
> What is the purpose of that test? If you intended to add a kprobe events
> with some offset so that it becomes ftrace-based kprobe, it should be
> a different test case, because

This is a follow up to:
http://lore.kernel.org/1664530538.ke6dp49pwh.naveen@linux.ibm.com

The intent is to add consecutive probes covering KPROBES_ON_FTRACE,
vanilla trap-based kprobes as well as optprobes to ensure all of those
and their interactions are good.

>
> - This is a test case for checking multiple (at least 256) kprobe events
> can be defined and enabled.
>
> - If you want to check the ftrace-based kprobe, it should be near the
> function entry, maybe within 16 bytes or so.
>
> - Also, you don't need to enable it at once (and should not for this case).
>
>> > The '|| true' is added with the echo statement to ignore errors that are
>> > caused by trying to add kprobes to non probeable lines and continue with
>> > the test.
>
> Can you add another test case for that? (and send it to the MLs which Cc'd
> to this mail)
> e.g.
>
> for i in `seq 0 16`; do
> echo p:testprobe $FUNCTION_FORK+${i} >> kprobe_events || continue
> echo 1 > events/kprobes/testprobe/enable
> ( echo "forked" )
> echo 0 > events/kprobes/testprobe/enable
> echo > kprobe_events
> done

The current test to add multiple kprobes within a function also falls
under the purview of multiple_kprobes.tc, but it can be split into a
separate multiple_kprobes_func.tc if you think that will be better.

>
>
> BTW, after we introduce the fprobe event (https://lore.kernel.org/linux-trace-kernel/166792255429.919356.14116090269057513181.stgit@devnote3/) that test case may be
> update to check fprobe events.

Indeed, I suppose that can be a separate test.


Thanks,
Naveen

>
> Thank you,
>
>> >
>> > Signed-off-by: Akanksha J N <akanksha@linux.ibm.com>
>> > ---
>> > .../selftests/ftrace/test.d/kprobe/multiple_kprobes.tc | 4 ++++
>> > 1 file changed, 4 insertions(+)
>>
>> Thanks for adding this test!
>>
>> >
>> > diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc b/tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc
>> > index be754f5bcf79..f005c2542baa 100644
>> > --- a/tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc
>> > +++ b/tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc
>> > @@ -25,6 +25,10 @@ if [ $L -ne 256 ]; then
>> > exit_fail
>> > fi
>> >
>> > +for i in `seq 0 255`; do
>> > + echo p $FUNCTION_FORK+${i} >> kprobe_events || true
>> > +done
>> > +
>> > cat kprobe_events >> $testlog
>> >
>> > echo 1 > events/kprobes/enable
>>
>> Thinking about this more, I wonder if we should add an explicit fork
>> after enabling the events, similar to kprobe_args.tc:
>> ( echo "forked" )
>>
>> That will ensure we hit all the probes we added. With that change:
>> Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>>
>>
>> - Naveen
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>
>

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