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

[sashiko-bot@kernel.org]

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