linux-kernel - Re: [PATCH] selftests/ftrace: Extend multiple_kprobes.tc to add multiple consecutive probes in a function

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Message-Id: <1673529279.3c5f8oes3z.naveen@linux.ibm.com>
Date:   Thu, 12 Jan 2023 18:51:14 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Akanksha J N <akanksha@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org
Cc:     mhiramat@...nel.org, rostedt@...dmis.org, shuah@...nel.org
Subject: Re: [PATCH] selftests/ftrace: Extend multiple_kprobes.tc to add
 multiple consecutive probes in a function

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.
> 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.
> 
> Signed-off-by: Akanksha J N <akanksha@...ux.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@...ux.vnet.ibm.com>


- Naveen