linux-kernel - Re: [PATCH] ftrace/selftest: Test combination of function

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Message-Id: <20240826001410.76bcc8304e7c3ee188420b5c@kernel.org>
Date: Mon, 26 Aug 2024 00:14:10 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Mark Rutland <mark.rutland@....com>, Shuah Khan <shuah@...nel.org>, Shuah
 Khan <skhan@...uxfoundation.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] ftrace/selftest: Test combination of function_graph
 tracer and function profiler

On Wed, 21 Aug 2024 15:09:03 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> Masami reported a bug when running function graph tracing then the
> function profiler. The following commands would cause a kernel crash:
> 
>   # cd /sys/kernel/tracing/
>   # echo function_graph > current_tracer
>   # echo 1 > function_profile_enabled
> 
> In that order. Create a test to test this two to make sure this does not
> come back as a regression.
> 
> Link: https://lore.kernel.org/172398528350.293426.8347220120333730248.stgit@devnote2

This looks good to me, but note that this depends on the above fix, unless
that, this may crash the kernel. I think the above fix should be merged in
v6.11-rcX so this may be safe for released kernel.

Thanks,

> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  .../ftrace/test.d/ftrace/fgraph-profiler.tc   | 30 +++++++++++++++++++
>  1 file changed, 30 insertions(+)
>  create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc
> new file mode 100644
> index 000000000000..62d44a1395da
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc
> @@ -0,0 +1,30 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +# description: ftrace - function profiler with function graph tracing
> +# requires: function_profile_enabled set_ftrace_filter function_graph:tracer
> +
> +# The function graph tracer can now be run along side of the function
> +# profiler. But there was a bug that caused the combination of the two
> +# to crash. It also required the function graph tracer to be started
> +# first.
> +#
> +# This test triggers that bug
> +#
> +# We need function_graph and profiling to to run this test
> +
> +fail() { # mesg
> +    echo $1
> +    exit_fail
> +}
> +
> +echo "Enabling function graph tracer:"
> +echo function_graph > current_tracer
> +echo "enable profiler"
> +
> +# Older kernels do not allow function_profile to be enabled with
> +# function graph tracer. If the below fails, mark it as unsupported
> +echo 1 > function_profile_enabled || exit_unsupported
> +
> +sleep 1
> +
> +exit 0
> -- 
> 2.43.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>