[PATCH] selftests/tracing: Fix test_multiple_writes stall

[PATCH] selftests/tracing: Fix test_multiple_writes stall

[Fushuai Wang]

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.
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@baidu.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");
 						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
+
+echo $ORIG > buffer_size_kb
-- 
2.36.1

Re: [PATCH] selftests/tracing: Fix test_multiple_writes stall

[Steven Rostedt]

On Fri, 26 Dec 2025 17:12:17 +0800
Fushuai Wang <fushuai.wang@linux.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@baidu.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

Re: [PATCH] selftests/tracing: Fix test_multiple_writes stall

[Fushuai Wang]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset=y, Size: 3074 bytes --]

>> 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.
>
>

Thank you for pointing this out. I will follow this guideline
in future submissions.

>> 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@baidu.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

Thank you, and this looks better.
I will send a v2 shortly.

---
Regards,
WANG