selftests/ftrace: Add test to exercize function tracer across cpu hotplug

Add a test to exercize cpu hotplug with the function tracer active to
ensure that sensitive functions in idle path are excluded from being
traced. This helps catch issues such as the one fixed by commit
4b3338aaa74d ("powerpc/ftrace: Fix stack teardown in ftrace_no_trace").

Signed-off-by: Naveen N Rao <naveen@kernel.org>
---
 .../ftrace/test.d/ftrace/func_hotplug.tc      | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc


base-commit: b85ea95d086471afb4ad062012a4d73cd328fa86

Hi Naveen,

On Tue, 12 Dec 2023 14:26:07 +0530
Naveen N Rao <naveen@kernel.org> wrote:

> Add a test to exercize cpu hotplug with the function tracer active to
> ensure that sensitive functions in idle path are excluded from being
> traced. This helps catch issues such as the one fixed by commit
> 4b3338aaa74d ("powerpc/ftrace: Fix stack teardown in ftrace_no_trace").
> 
> Signed-off-by: Naveen N Rao <naveen@kernel.org>
> ---
>  .../ftrace/test.d/ftrace/func_hotplug.tc      | 30 +++++++++++++++++++
>  1 file changed, 30 insertions(+)
>  create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> new file mode 100644
> index 000000000000..49731a2b5c23
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> @@ -0,0 +1,30 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +# description: ftrace - function trace across cpu hotplug
> +# requires: function:tracer
> +
> +if ! which nproc ; then
> +  nproc() {
> +    ls -d /sys/devices/system/cpu/cpu[0-9]* | wc -l
> +  }
> +fi
> +
> +NP=`nproc`
> +
> +if [ $NP -eq 1 ] ;then
> +  echo "We can not test cpu hotplug in UP environment"
> +  exit_unresolved
> +fi

This looks good, but can you find the 2nd online CPU before
this test?
I mean, there is a case that cpu1 is already offlined and others
like cpu2 is onlined. So we need to use the 2nd online cpu.

Thank you,

> +
> +echo 0 > tracing_on
> +echo > trace
> +: "Set CPU1 offline/online with function tracer enabled"
> +echo function > current_tracer
> +echo 1 > tracing_on
> +(echo 0 > /sys/devices/system/cpu/cpu1/online)
> +(echo "forked"; sleep 1)
> +(echo 1 > /sys/devices/system/cpu/cpu1/online)
> +echo 0 > tracing_on
> +
> +: "Check CPU1 events are recorded"
> +grep -q -e "\[001\]" trace
> 
> base-commit: b85ea95d086471afb4ad062012a4d73cd328fa86
> -- 
> 2.43.0
>

On Wed, Dec 13, 2023 at 09:40:38AM +0900, Masami Hiramatsu wrote:
> Hi Naveen,
> 
> On Tue, 12 Dec 2023 14:26:07 +0530
> Naveen N Rao <naveen@kernel.org> wrote:
> 
> > Add a test to exercize cpu hotplug with the function tracer active to
> > ensure that sensitive functions in idle path are excluded from being
> > traced. This helps catch issues such as the one fixed by commit
> > 4b3338aaa74d ("powerpc/ftrace: Fix stack teardown in ftrace_no_trace").
> > 
> > Signed-off-by: Naveen N Rao <naveen@kernel.org>
> > ---
> >  .../ftrace/test.d/ftrace/func_hotplug.tc      | 30 +++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> > 
> > diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> > new file mode 100644
> > index 000000000000..49731a2b5c23
> > --- /dev/null
> > +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> > @@ -0,0 +1,30 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0
> > +# description: ftrace - function trace across cpu hotplug
> > +# requires: function:tracer
> > +
> > +if ! which nproc ; then
> > +  nproc() {
> > +    ls -d /sys/devices/system/cpu/cpu[0-9]* | wc -l
> > +  }
> > +fi
> > +
> > +NP=`nproc`
> > +
> > +if [ $NP -eq 1 ] ;then
> > +  echo "We can not test cpu hotplug in UP environment"
> > +  exit_unresolved
> > +fi
> 
> This looks good, but can you find the 2nd online CPU before
> this test?
> I mean, there is a case that cpu1 is already offlined and others
> like cpu2 is onlined. So we need to use the 2nd online cpu.

Good point, thanks. I will send a v2.

- Naveen