[PATCH] perf data convert json: Fix trace_seq memory leak in process_sample_event()

[PATCH] perf data convert json: Fix trace_seq memory leak in process_sample_event()

[Tanushree Shah]

Unlike the in-kernel trace_seq which uses a statically allocated buffer,
the userspace traceevent library's trace_seq uses a dynamically allocated
one. Therefore, every trace_seq_init() call must be paired with a
trace_seq_destroy(), otherwise it produces a memory leak.

In process_sample_event(), a trace_seq is initialized for each field when
formatting tracepoint raw_data, but the matching trace_seq_destroy() is
never called, leaking memory for every field of every sample processed.

Add the missing trace_seq_destroy() after using the trace_seq buffer to
properly free the allocated memory.

Detected with Valgrind on a perf.data file with 2,729 tracepoint samples:
  Before: definitely lost: 55,537,664 bytes in 13,559 blocks
  After:  definitely lost: 0 bytes in 0 blocks

Fixes: 9d895e468429 ("perf data: Add tracepoint fields when converting to JSON")
Signed-off-by: Tanushree Shah <tshah@linux.ibm.com>
---
 tools/perf/util/data-convert-json.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
index d526c91312ed..6dd9349ab10f 100644
--- a/tools/perf/util/data-convert-json.c
+++ b/tools/perf/util/data-convert-json.c
@@ -257,6 +257,7 @@ static int process_sample_event(const struct perf_tool *tool,
 				trace_seq_init(&s);
 				tep_print_field(&s, sample->raw_data, fields[i]);
 				output_json_key_string(out, true, 3, fields[i]->name, s.buffer);
+				trace_seq_destroy(&s);
 
 				i++;
 			}
-- 
2.47.3

Re: [PATCH] perf data convert json: Fix trace_seq memory leak in process_sample_event()

[Arnaldo Carvalho de Melo]

On Thu, Jun 04, 2026 at 12:25:19PM +0530, Tanushree Shah wrote:
> Unlike the in-kernel trace_seq which uses a statically allocated buffer,
> the userspace traceevent library's trace_seq uses a dynamically allocated
> one. Therefore, every trace_seq_init() call must be paired with a
> trace_seq_destroy(), otherwise it produces a memory leak.
> 
> In process_sample_event(), a trace_seq is initialized for each field when
> formatting tracepoint raw_data, but the matching trace_seq_destroy() is
> never called, leaking memory for every field of every sample processed.
> 
> Add the missing trace_seq_destroy() after using the trace_seq buffer to
> properly free the allocated memory.
> 
> Detected with Valgrind on a perf.data file with 2,729 tracepoint samples:
>   Before: definitely lost: 55,537,664 bytes in 13,559 blocks
>   After:  definitely lost: 0 bytes in 0 blocks

Thanks, applied to perf-tools-next, for v7.2.

- Arnaldo
 
> Fixes: 9d895e468429 ("perf data: Add tracepoint fields when converting to JSON")
> Signed-off-by: Tanushree Shah <tshah@linux.ibm.com>
> ---
>  tools/perf/util/data-convert-json.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
> index d526c91312ed..6dd9349ab10f 100644
> --- a/tools/perf/util/data-convert-json.c
> +++ b/tools/perf/util/data-convert-json.c
> @@ -257,6 +257,7 @@ static int process_sample_event(const struct perf_tool *tool,
>  				trace_seq_init(&s);
>  				tep_print_field(&s, sample->raw_data, fields[i]);
>  				output_json_key_string(out, true, 3, fields[i]->name, s.buffer);
> +				trace_seq_destroy(&s);
>  
>  				i++;
>  			}
> -- 
> 2.47.3

Re: [PATCH] perf data convert json: Fix trace_seq memory leak in process_sample_event()

[Tanushree Shah]

Hello Arnaldo

Thanks for checking the patch. I cannot see this patch applied on 
perf-tools-next yet.

https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/log/?h=perf-tools-next

Thanks.

On 05/06/26 02:59, Arnaldo Carvalho de Melo wrote:
> On Thu, Jun 04, 2026 at 12:25:19PM +0530, Tanushree Shah wrote:
>> Unlike the in-kernel trace_seq which uses a statically allocated buffer,
>> the userspace traceevent library's trace_seq uses a dynamically allocated
>> one. Therefore, every trace_seq_init() call must be paired with a
>> trace_seq_destroy(), otherwise it produces a memory leak.
>>
>> In process_sample_event(), a trace_seq is initialized for each field when
>> formatting tracepoint raw_data, but the matching trace_seq_destroy() is
>> never called, leaking memory for every field of every sample processed.
>>
>> Add the missing trace_seq_destroy() after using the trace_seq buffer to
>> properly free the allocated memory.
>>
>> Detected with Valgrind on a perf.data file with 2,729 tracepoint samples:
>>    Before: definitely lost: 55,537,664 bytes in 13,559 blocks
>>    After:  definitely lost: 0 bytes in 0 blocks
> 
> Thanks, applied to perf-tools-next, for v7.2.
> 
> - Arnaldo
>   
>> Fixes: 9d895e468429 ("perf data: Add tracepoint fields when converting to JSON")
>> Signed-off-by: Tanushree Shah <tshah@linux.ibm.com>
>> ---
>>   tools/perf/util/data-convert-json.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
>> index d526c91312ed..6dd9349ab10f 100644
>> --- a/tools/perf/util/data-convert-json.c
>> +++ b/tools/perf/util/data-convert-json.c
>> @@ -257,6 +257,7 @@ static int process_sample_event(const struct perf_tool *tool,
>>   				trace_seq_init(&s);
>>   				tep_print_field(&s, sample->raw_data, fields[i]);
>>   				output_json_key_string(out, true, 3, fields[i]->name, s.buffer);
>> +				trace_seq_destroy(&s);
>>   
>>   				i++;
>>   			}
>> -- 
>> 2.47.3