linux-kernel - Re: [PATCH] selftests/tracing: Fix test_multiple

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Message-ID: <20251226132927.4c406bd9@gandalf.local.home>
Date: Fri, 26 Dec 2025 13:29:27 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Fushuai Wang <fushuai.wang@...ux.dev>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com, shuah@...nel.org,
 wangfushuai@...du.com, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] selftests/tracing: Fix test_multiple_writes stall

On Fri, 26 Dec 2025 17:12:17 +0800
Fushuai Wang <fushuai.wang@...ux.dev> wrote:

> When /sys/kernel/tracing/buffer_size_kb is less than 12KB,
> the test_multiple_writes test will stall and wait for more
> input due to insufficient buffer space.
> 
> This patch check current buffer_size_kb value before the test.

Never use "This patch" in a change log. See Submitting Patches:

https://docs.kernel.org/process/submitting-patches.html#describe-your-changes

    Describe your changes in imperative mood, e.g. “make xyzzy do frotz”
    instead of “[This patch] makes xyzzy do frotz” or “[I] changed xyzzy to
    do frotz”, as if you are giving orders to the codebase to change its
    behaviour.


> If it is less than 12KB, it temporarily increase the buffer to
> 12KB, and restore the original value after the tests are completed.
> 
> Fixes: 37f46601383a ("selftests/tracing: Add basic test for trace_marker_raw file")
> Signed-off-by: Fushuai Wang <wangfushuai@...du.com>
> ---
>  .../ftrace/test.d/00basic/trace_marker_raw.tc    | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> index 7daf7292209e..216f87d89c3f 100644
> --- a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> +++ b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> @@ -58,7 +58,7 @@ test_multiple_writes() {
>  	echo stop > trace_marker
>  
>  	# Check to make sure the number of entries is the id (rounded up by 4)
> -	awk '/.*: # [0-9a-f]* / {
> +	awk -v ORIG="${ORIG}" '/.*: # [0-9a-f]* / {
>  			print;
>  			cnt = -1;
>  			for (i = 0; i < NF; i++) {
> @@ -70,6 +70,7 @@ test_multiple_writes() {
>  					# The number of items is always rounded up by 4
>  					cnt2 = int((cnt + 3) / 4) * 4;
>  					if (cnt2 != num) {
> +						system("echo \""ORIG"\" > buffer_size_kb");

Why are you doing this in the awk script?

>  						exit 1;
>  					}
>  					break;
> @@ -89,6 +90,7 @@ test_buffer() {
>  	# The id must be four bytes, test that 3 bytes fails a write
>  	if echo -n abc > ./trace_marker_raw ; then
>  		echo "Too small of write expected to fail but did not"
> +		echo $ORIG > buffer_size_kb
>  		exit_fail
>  	fi
>  
> @@ -99,9 +101,21 @@ test_buffer() {
>  
>  	if write_buffer 0xdeadbeef $size ; then
>  		echo "Too big of write expected to fail but did not"
> +		echo $ORIG > buffer_size_kb
>  		exit_fail
>  	fi
>  }
>  
> +ORIG=`cat buffer_size_kb`
> +
> +# test_multiple_writes test needs at least 12KB buffer
> +NEW_SIZE=12
> +
> +if [ ${ORIG} -lt ${NEW_SIZE} ]; then
> +	echo ${NEW_SIZE} > buffer_size_kb
> +fi
> +
>  test_buffer
>  test_multiple_writes

Could add:

  if ! test_multiple_writes ; then
	echo $ORIG > buffer_size_kb
	exit_fail
  fi

instead.

-- Steve

> +
> +echo $ORIG > buffer_size_kb