[PATCH 0/4] perf timechart: Small optimization for backtrace

[PATCH 0/4] perf timechart: Small optimization for backtrace

[Namhyung Kim]

Hello,

I found an issue int timechart backtrace handling during the last review.
The goal is to reduce unnecessary work in generating backtrace string.

Thanks,
Namhyung


Namhyung Kim (4):
  perf timechart: Don't pass @event to cat_backtrace()
  perf timechart: Generate backtrace only if needed
  perf timechart: Remove unused backtrace in trace_handler
  perf timechart: Remove unnecessary copy of backtrace

 tools/perf/builtin-timechart.c | 88 ++++++++++++++--------------------
 1 file changed, 36 insertions(+), 52 deletions(-)

-- 
2.54.0.1032.g2f8565e1d1-goog

[PATCH 1/4] perf timechart: Don't pass @event to cat_backtrace()

[Namhyung Kim]

The cat_backtrace() is only called from process_sample_event() which
means the event type is always PERF_RECORD_SAMPLE.  We don't need to
pass the event just because to print already known info.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-timechart.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
index 85a9ad0455aecccd..dafd361ecf9d8cd7 100644
--- a/tools/perf/builtin-timechart.c
+++ b/tools/perf/builtin-timechart.c
@@ -493,8 +493,7 @@ static void sched_switch(struct timechart *tchart, int cpu, u64 timestamp,
  * Returns a malloc'd backtrace string built via open_memstream, or NULL
  * on error.  Caller must free() the returned pointer.
  */
-static char *cat_backtrace(union perf_event *event,
-			   struct perf_sample *sample,
+static char *cat_backtrace(struct perf_sample *sample,
 			   struct machine *machine)
 {
 	struct addr_location al;
@@ -516,9 +515,8 @@ static char *cat_backtrace(union perf_event *event,
 		goto exit;
 
 	if (machine__resolve(machine, &al, sample) < 0) {
-		pr_err("problem processing %s (%u) event at offset %#" PRIx64 ", skipping it.\n",
-		       perf_event__name(event->header.type), event->header.type,
-		       sample->file_offset);
+		pr_err("problem processing SAMPLE (%u) event at offset %#" PRIx64 ", skipping it.\n",
+		       PERF_RECORD_SAMPLE, sample->file_offset);
 		goto exit;
 	}
 
@@ -578,7 +576,7 @@ typedef int (*tracepoint_handler)(struct timechart *tchart,
 				  const char *backtrace);
 
 static int process_sample_event(const struct perf_tool *tool,
-				union perf_event *event,
+				union perf_event *event __maybe_unused,
 				struct perf_sample *sample,
 				struct machine *machine)
 {
@@ -595,7 +593,7 @@ static int process_sample_event(const struct perf_tool *tool,
 
 	if (evsel->handler != NULL) {
 		tracepoint_handler f = evsel->handler;
-		char *backtrace = cat_backtrace(event, sample, machine);
+		char *backtrace = cat_backtrace(sample, machine);
 
 		ret = f(tchart, sample, backtrace);
 		free(backtrace);
-- 
2.54.0.1032.g2f8565e1d1-goog

[PATCH 2/4] perf timechart: Generate backtrace only if needed

[Namhyung Kim]

The backtrace was used by sched-switch and sched-wakeup only.  No need
to call cat_backtrace() in the process_sample_event().  Let's pass NULL
backtrace and generate it from the sched events.

As it needs a pointer to the 'machine', let's save the session in the
timechart struct and use the host machine of the session instead of
passing the pointer to all handlers.  It should be fine to assume the
host machine as timechart command doesn't deal with guest machines and
there's no way to get tracepoints from the guest events.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-timechart.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
index dafd361ecf9d8cd7..337ae547d008ea0b 100644
--- a/tools/perf/builtin-timechart.c
+++ b/tools/perf/builtin-timechart.c
@@ -56,6 +56,7 @@ struct timechart {
 	struct per_pid		*all_data;
 	struct power_event	*power_events;
 	struct wake_event	*wake_events;
+	struct perf_session	*session;
 	int			proc_num;
 	unsigned int		numcpus;
 	u64			min_freq,	/* Lowest CPU frequency seen */
@@ -578,7 +579,7 @@ typedef int (*tracepoint_handler)(struct timechart *tchart,
 static int process_sample_event(const struct perf_tool *tool,
 				union perf_event *event __maybe_unused,
 				struct perf_sample *sample,
-				struct machine *machine)
+				struct machine *machine __maybe_unused)
 {
 	struct timechart *tchart = container_of(tool, struct timechart, tool);
 	struct evsel *evsel = sample->evsel;
@@ -593,10 +594,8 @@ static int process_sample_event(const struct perf_tool *tool,
 
 	if (evsel->handler != NULL) {
 		tracepoint_handler f = evsel->handler;
-		char *backtrace = cat_backtrace(sample, machine);
 
-		ret = f(tchart, sample, backtrace);
-		free(backtrace);
+		ret = f(tchart, sample, NULL);
 	}
 
 	return ret;
@@ -656,7 +655,10 @@ process_sample_sched_wakeup(struct timechart *tchart,
 			 sample->file_offset, sample->cpu);
 		return -1;
 	}
+
+	backtrace = cat_backtrace(sample, &tchart->session->machines.host);
 	sched_wakeup(tchart, sample->cpu, sample->time, waker, wakee, flags, backtrace);
+	free((char *)backtrace);
 	return 0;
 }
 
@@ -675,8 +677,11 @@ process_sample_sched_switch(struct timechart *tchart,
 			 sample->file_offset, sample->cpu);
 		return -1;
 	}
+
+	backtrace = cat_backtrace(sample, &tchart->session->machines.host);
 	sched_switch(tchart, sample->cpu, sample->time, prev_pid, next_pid,
 		     prev_state, backtrace);
+	free((char *)backtrace);
 	return 0;
 }
 
@@ -1661,6 +1666,7 @@ static int __cmd_timechart(struct timechart *tchart, const char *output_name)
 	if (IS_ERR(session))
 		return PTR_ERR(session);
 
+	tchart->session = session;
 	symbol__init(perf_session__env(session));
 
 	(void)perf_header__process_sections(&session->header,
-- 
2.54.0.1032.g2f8565e1d1-goog

[PATCH 3/4] perf timechart: Remove unused backtrace in trace_handler

[Namhyung Kim]

Now the backtrace argument is not used in any handler.  Let's get rid of
it.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-timechart.c | 64 ++++++++++++----------------------
 1 file changed, 23 insertions(+), 41 deletions(-)

diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
index 337ae547d008ea0b..4efac73a714c5e5f 100644
--- a/tools/perf/builtin-timechart.c
+++ b/tools/perf/builtin-timechart.c
@@ -573,8 +573,7 @@ static char *cat_backtrace(struct perf_sample *sample,
 }
 
 typedef int (*tracepoint_handler)(struct timechart *tchart,
-				  struct perf_sample *sample,
-				  const char *backtrace);
+				  struct perf_sample *sample);
 
 static int process_sample_event(const struct perf_tool *tool,
 				union perf_event *event __maybe_unused,
@@ -595,7 +594,7 @@ static int process_sample_event(const struct perf_tool *tool,
 	if (evsel->handler != NULL) {
 		tracepoint_handler f = evsel->handler;
 
-		ret = f(tchart, sample, NULL);
+		ret = f(tchart, sample);
 	}
 
 	return ret;
@@ -603,8 +602,7 @@ static int process_sample_event(const struct perf_tool *tool,
 
 static int
 process_sample_cpu_idle(struct timechart *tchart __maybe_unused,
-			struct perf_sample *sample,
-			const char *backtrace __maybe_unused)
+			struct perf_sample *sample)
 {
 	u32 state  = perf_sample__intval(sample, "state");
 	u32 cpu_id = perf_sample__intval(sample, "cpu_id");
@@ -624,8 +622,7 @@ process_sample_cpu_idle(struct timechart *tchart __maybe_unused,
 
 static int
 process_sample_cpu_frequency(struct timechart *tchart,
-			     struct perf_sample *sample,
-			     const char *backtrace __maybe_unused)
+			     struct perf_sample *sample)
 {
 	u32 state  = perf_sample__intval(sample, "state");
 	u32 cpu_id = perf_sample__intval(sample, "cpu_id");
@@ -642,12 +639,12 @@ process_sample_cpu_frequency(struct timechart *tchart,
 
 static int
 process_sample_sched_wakeup(struct timechart *tchart,
-			    struct perf_sample *sample,
-			    const char *backtrace)
+			    struct perf_sample *sample)
 {
 	u8 flags  = perf_sample__intval(sample, "common_flags");
 	int waker = perf_sample__intval(sample, "common_pid");
 	int wakee = perf_sample__intval(sample, "pid");
+	char *backtrace;
 
 	/* perf.data is untrusted input — CPU may be absent or corrupted */
 	if (sample->cpu >= MAX_CPUS) {
@@ -664,12 +661,12 @@ process_sample_sched_wakeup(struct timechart *tchart,
 
 static int
 process_sample_sched_switch(struct timechart *tchart,
-			    struct perf_sample *sample,
-			    const char *backtrace)
+			    struct perf_sample *sample)
 {
 	int prev_pid   = perf_sample__intval(sample, "prev_pid");
 	int next_pid   = perf_sample__intval(sample, "next_pid");
 	u64 prev_state = perf_sample__intval(sample, "prev_state");
+	char *backtrace;
 
 	/* perf.data is untrusted input — CPU may be absent or corrupted */
 	if (sample->cpu >= MAX_CPUS) {
@@ -688,8 +685,7 @@ process_sample_sched_switch(struct timechart *tchart,
 #ifdef SUPPORT_OLD_POWER_EVENTS
 static int
 process_sample_power_start(struct timechart *tchart __maybe_unused,
-			   struct perf_sample *sample,
-			   const char *backtrace __maybe_unused)
+			   struct perf_sample *sample)
 {
 	u64 cpu_id = perf_sample__intval(sample, "cpu_id");
 	u64 value  = perf_sample__intval(sample, "value");
@@ -706,8 +702,7 @@ process_sample_power_start(struct timechart *tchart __maybe_unused,
 
 static int
 process_sample_power_end(struct timechart *tchart,
-			 struct perf_sample *sample,
-			 const char *backtrace __maybe_unused)
+			 struct perf_sample *sample)
 {
 	/* perf.data is untrusted input — CPU may be absent or corrupted */
 	if (sample->cpu >= MAX_CPUS) {
@@ -721,8 +716,7 @@ process_sample_power_end(struct timechart *tchart,
 
 static int
 process_sample_power_frequency(struct timechart *tchart,
-			       struct perf_sample *sample,
-			       const char *backtrace __maybe_unused)
+			       struct perf_sample *sample)
 {
 	u64 cpu_id = perf_sample__intval(sample, "cpu_id");
 	u64 value  = perf_sample__intval(sample, "value");
@@ -895,8 +889,7 @@ static int pid_end_io_sample(struct timechart *tchart, int pid, int type,
 
 static int
 process_enter_read(struct timechart *tchart,
-		   struct perf_sample *sample,
-		   const char *backtrace __maybe_unused)
+		   struct perf_sample *sample)
 {
 	long fd = perf_sample__intval(sample, "fd");
 	return pid_begin_io_sample(tchart, sample->tid, IOTYPE_READ,
@@ -905,8 +898,7 @@ process_enter_read(struct timechart *tchart,
 
 static int
 process_exit_read(struct timechart *tchart,
-		  struct perf_sample *sample,
-		  const char *backtrace __maybe_unused)
+		  struct perf_sample *sample)
 {
 	long ret = perf_sample__intval(sample, "ret");
 	return pid_end_io_sample(tchart, sample->tid, IOTYPE_READ,
@@ -915,8 +907,7 @@ process_exit_read(struct timechart *tchart,
 
 static int
 process_enter_write(struct timechart *tchart,
-		    struct perf_sample *sample,
-		    const char *backtrace __maybe_unused)
+		    struct perf_sample *sample)
 {
 	long fd = perf_sample__intval(sample, "fd");
 	return pid_begin_io_sample(tchart, sample->tid, IOTYPE_WRITE,
@@ -925,8 +916,7 @@ process_enter_write(struct timechart *tchart,
 
 static int
 process_exit_write(struct timechart *tchart,
-		   struct perf_sample *sample,
-		   const char *backtrace __maybe_unused)
+		   struct perf_sample *sample)
 {
 	long ret = perf_sample__intval(sample, "ret");
 	return pid_end_io_sample(tchart, sample->tid, IOTYPE_WRITE,
@@ -935,8 +925,7 @@ process_exit_write(struct timechart *tchart,
 
 static int
 process_enter_sync(struct timechart *tchart,
-		   struct perf_sample *sample,
-		   const char *backtrace __maybe_unused)
+		   struct perf_sample *sample)
 {
 	long fd = perf_sample__intval(sample, "fd");
 	return pid_begin_io_sample(tchart, sample->tid, IOTYPE_SYNC,
@@ -945,8 +934,7 @@ process_enter_sync(struct timechart *tchart,
 
 static int
 process_exit_sync(struct timechart *tchart,
-		  struct perf_sample *sample,
-		  const char *backtrace __maybe_unused)
+		  struct perf_sample *sample)
 {
 	long ret = perf_sample__intval(sample, "ret");
 	return pid_end_io_sample(tchart, sample->tid, IOTYPE_SYNC,
@@ -955,8 +943,7 @@ process_exit_sync(struct timechart *tchart,
 
 static int
 process_enter_tx(struct timechart *tchart,
-		 struct perf_sample *sample,
-		 const char *backtrace __maybe_unused)
+		 struct perf_sample *sample)
 {
 	long fd = perf_sample__intval(sample, "fd");
 	return pid_begin_io_sample(tchart, sample->tid, IOTYPE_TX,
@@ -965,8 +952,7 @@ process_enter_tx(struct timechart *tchart,
 
 static int
 process_exit_tx(struct timechart *tchart,
-		struct perf_sample *sample,
-		const char *backtrace __maybe_unused)
+		struct perf_sample *sample)
 {
 	long ret = perf_sample__intval(sample, "ret");
 	return pid_end_io_sample(tchart, sample->tid, IOTYPE_TX,
@@ -975,8 +961,7 @@ process_exit_tx(struct timechart *tchart,
 
 static int
 process_enter_rx(struct timechart *tchart,
-		 struct perf_sample *sample,
-		 const char *backtrace __maybe_unused)
+		 struct perf_sample *sample)
 {
 	long fd = perf_sample__intval(sample, "fd");
 	return pid_begin_io_sample(tchart, sample->tid, IOTYPE_RX,
@@ -985,8 +970,7 @@ process_enter_rx(struct timechart *tchart,
 
 static int
 process_exit_rx(struct timechart *tchart,
-		struct perf_sample *sample,
-		const char *backtrace __maybe_unused)
+		struct perf_sample *sample)
 {
 	long ret = perf_sample__intval(sample, "ret");
 	return pid_end_io_sample(tchart, sample->tid, IOTYPE_RX,
@@ -995,8 +979,7 @@ process_exit_rx(struct timechart *tchart,
 
 static int
 process_enter_poll(struct timechart *tchart,
-		   struct perf_sample *sample,
-		   const char *backtrace __maybe_unused)
+		   struct perf_sample *sample)
 {
 	long fd = perf_sample__intval(sample, "fd");
 	return pid_begin_io_sample(tchart, sample->tid, IOTYPE_POLL,
@@ -1005,8 +988,7 @@ process_enter_poll(struct timechart *tchart,
 
 static int
 process_exit_poll(struct timechart *tchart,
-		  struct perf_sample *sample,
-		  const char *backtrace __maybe_unused)
+		  struct perf_sample *sample)
 {
 	long ret = perf_sample__intval(sample, "ret");
 	return pid_end_io_sample(tchart, sample->tid, IOTYPE_POLL,
-- 
2.54.0.1032.g2f8565e1d1-goog

[PATCH 4/4] perf timechart: Remove unnecessary copy of backtrace

[Namhyung Kim]

The pattern of strdup() and free() is found, and I think it just can
use the original backtrace directly.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-timechart.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
index 4efac73a714c5e5f..2fd24d3aaa837743 100644
--- a/tools/perf/builtin-timechart.c
+++ b/tools/perf/builtin-timechart.c
@@ -300,7 +300,7 @@ static void pid_put_sample(struct timechart *tchart, int pid, int type,
 	sample->type = type;
 	sample->next = c->samples;
 	sample->cpu = cpu;
-	sample->backtrace = backtrace ? strdup(backtrace) : NULL;
+	sample->backtrace = backtrace;
 	c->samples = sample;
 
 	if (sample->type == TYPE_RUNNING && end > start && start > 0) {
@@ -434,7 +434,7 @@ static void sched_wakeup(struct timechart *tchart, int cpu, u64 timestamp,
 
 	we->time = timestamp;
 	we->waker = waker;
-	we->backtrace = backtrace ? strdup(backtrace) : NULL;
+	we->backtrace = backtrace;
 
 	if ((flags & TRACE_FLAG_HARDIRQ) || (flags & TRACE_FLAG_SOFTIRQ))
 		we->waker = -1;
@@ -655,7 +655,6 @@ process_sample_sched_wakeup(struct timechart *tchart,
 
 	backtrace = cat_backtrace(sample, &tchart->session->machines.host);
 	sched_wakeup(tchart, sample->cpu, sample->time, waker, wakee, flags, backtrace);
-	free((char *)backtrace);
 	return 0;
 }
 
@@ -678,7 +677,6 @@ process_sample_sched_switch(struct timechart *tchart,
 	backtrace = cat_backtrace(sample, &tchart->session->machines.host);
 	sched_switch(tchart, sample->cpu, sample->time, prev_pid, next_pid,
 		     prev_state, backtrace);
-	free((char *)backtrace);
 	return 0;
 }
 
-- 
2.54.0.1032.g2f8565e1d1-goog

Re: [PATCH 4/4] perf timechart: Remove unnecessary copy of backtrace

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Removing `free(backtrace)` causes severe memory leaks when the backtrace string is not consumed by the sample tracking logic.
--

commit 8d24fd58d3a0d2702142c45fce31ca640b59f748
Author: Namhyung Kim <namhyung@kernel.org>

perf timechart: Remove unnecessary copy of backtrace

This commit updates timechart to use the backtrace string directly instead
of duplicating it with strdup(). It updates pid_put_sample() and
sched_wakeup() to store the original pointer and removes the free()
calls in the process_sample routines.

> diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
> index 4efac73a714c5..2fd24d3aaa837 100644
> --- a/tools/perf/builtin-timechart.c
> +++ b/tools/perf/builtin-timechart.c

[ ... ]

> @@ -434,7 +434,7 @@ static void sched_wakeup(struct timechart *tchart, int cpu, u64 timestamp,
>  
>  	we->time = timestamp;
>  	we->waker = waker;
> -	we->backtrace = backtrace ? strdup(backtrace) : NULL;
> +	we->backtrace = backtrace;

[Severity: Medium]
Does this leak the dynamically allocated backtrace string from
cat_backtrace() if the wake_event allocation fails?

tools/perf/builtin-timechart.c:sched_wakeup() {
	struct wake_event *we = zalloc(sizeof(*we));

	if (!we)
		return;
    ...
}

Because the unconditional free() was removed from
process_sample_sched_wakeup(), the backtrace pointer is dropped and
leaked if zalloc() fails.

>  
>  	if ((flags & TRACE_FLAG_HARDIRQ) || (flags & TRACE_FLAG_SOFTIRQ))
>  		we->waker = -1;

[ ... ]

> @@ -678,7 +677,6 @@ process_sample_sched_switch(struct timechart *tchart,
>  	backtrace = cat_backtrace(sample, &tchart->session->machines.host);
>  	sched_switch(tchart, sample->cpu, sample->time, prev_pid, next_pid,
>  		     prev_state, backtrace);
> -	free((char *)backtrace);

[Severity: Medium]
Will this leak the backtrace string if sched_switch() does not consume it?

tools/perf/builtin-timechart.c:sched_switch() {
	if (prev_p->current && prev_p->current->state != TYPE_NONE)
		pid_put_sample(tchart, prev_pid, TYPE_RUNNING, cpu,
			       prev_p->current->state_since, timestamp,
			       backtrace);

	if (p && p->current) {
		if (p->current->state != TYPE_NONE)
			pid_put_sample(tchart, next_pid, p->current->state, cpu,
				       p->current->state_since, timestamp,
				       backtrace);
	}
    ...
}

If both TYPE_NONE conditions evaluate to true, pid_put_sample() is not
called. The backtrace string goes unreferenced and is permanently lost
now that the unconditional free() has been removed.

>  	return 0;
>  }
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260604190812.2168118-1-namhyung@kernel.org?part=4

Re: [PATCH 4/4] perf timechart: Remove unnecessary copy of backtrace

[Arnaldo Carvalho de Melo]

On Thu, Jun 04, 2026 at 07:18:17PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Removing `free(backtrace)` causes severe memory leaks when the backtrace string is not consumed by the sample tracking logic.
> --

From a quick look the suggestions seems legit, will wait for v2 then.

- Arnaldo
 
> commit 8d24fd58d3a0d2702142c45fce31ca640b59f748
> Author: Namhyung Kim <namhyung@kernel.org>
> 
> perf timechart: Remove unnecessary copy of backtrace
> 
> This commit updates timechart to use the backtrace string directly instead
> of duplicating it with strdup(). It updates pid_put_sample() and
> sched_wakeup() to store the original pointer and removes the free()
> calls in the process_sample routines.
> 
> > diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
> > index 4efac73a714c5..2fd24d3aaa837 100644
> > --- a/tools/perf/builtin-timechart.c
> > +++ b/tools/perf/builtin-timechart.c
> 
> [ ... ]
> 
> > @@ -434,7 +434,7 @@ static void sched_wakeup(struct timechart *tchart, int cpu, u64 timestamp,
> >  
> >  	we->time = timestamp;
> >  	we->waker = waker;
> > -	we->backtrace = backtrace ? strdup(backtrace) : NULL;
> > +	we->backtrace = backtrace;
> 
> [Severity: Medium]
> Does this leak the dynamically allocated backtrace string from
> cat_backtrace() if the wake_event allocation fails?
> 
> tools/perf/builtin-timechart.c:sched_wakeup() {
> 	struct wake_event *we = zalloc(sizeof(*we));
> 
> 	if (!we)
> 		return;
>     ...
> }
> 
> Because the unconditional free() was removed from
> process_sample_sched_wakeup(), the backtrace pointer is dropped and
> leaked if zalloc() fails.
> 
> >  
> >  	if ((flags & TRACE_FLAG_HARDIRQ) || (flags & TRACE_FLAG_SOFTIRQ))
> >  		we->waker = -1;
> 
> [ ... ]
> 
> > @@ -678,7 +677,6 @@ process_sample_sched_switch(struct timechart *tchart,
> >  	backtrace = cat_backtrace(sample, &tchart->session->machines.host);
> >  	sched_switch(tchart, sample->cpu, sample->time, prev_pid, next_pid,
> >  		     prev_state, backtrace);
> > -	free((char *)backtrace);
> 
> [Severity: Medium]
> Will this leak the backtrace string if sched_switch() does not consume it?
> 
> tools/perf/builtin-timechart.c:sched_switch() {
> 	if (prev_p->current && prev_p->current->state != TYPE_NONE)
> 		pid_put_sample(tchart, prev_pid, TYPE_RUNNING, cpu,
> 			       prev_p->current->state_since, timestamp,
> 			       backtrace);
> 
> 	if (p && p->current) {
> 		if (p->current->state != TYPE_NONE)
> 			pid_put_sample(tchart, next_pid, p->current->state, cpu,
> 				       p->current->state_since, timestamp,
> 				       backtrace);
> 	}
>     ...
> }
> 
> If both TYPE_NONE conditions evaluate to true, pid_put_sample() is not
> called. The backtrace string goes unreferenced and is permanently lost
> now that the unconditional free() has been removed.
> 
> >  	return 0;
> >  }
> >
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260604190812.2168118-1-namhyung@kernel.org?part=4

Re: [PATCH 4/4] perf timechart: Remove unnecessary copy of backtrace

[Namhyung Kim]

On Thu, Jun 04, 2026 at 05:15:02PM -0300, Arnaldo Carvalho de Melo wrote:
> On Thu, Jun 04, 2026 at 07:18:17PM +0000, sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > - [Medium] Removing `free(backtrace)` causes severe memory leaks when the backtrace string is not consumed by the sample tracking logic.
> > --
> 
> From a quick look the suggestions seems legit, will wait for v2 then.

Yep, will send out soon.

Thanks,
Namhyung