Re: [PATCH v1 05/13] perf synthetic-events: Fix uninitialized pthread_join

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Divide by zero crash in perf_event__synthesize_threads when no tasks are found.
--

commit 30888fa2ce27193736ae38293c89b11a5e47a514
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix uninitialized pthread_join

This commit fixes an uninitialized pthread_join() call when thread creation
fails in perf_event__synthesize_threads() by ensuring only successfully
created threads are joined.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index b75f9dcf4dbfe..35de41ad14d33 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -1104,8 +1104,8 @@ int perf_event__synthesize_threads(const struct perf_tool *tool,

[Severity: High]
This is a pre-existing issue, but does this code suffer from a fatal
division by zero when no tasks are found?

If scandir() finds no matching tasks in /proc (which can happen in an empty
chroot or isolated container), n is 0. If the system has multiple CPU cores
(thread_nr > 1), we bypass the single-thread fast path.

perf_event__synthesize_threads() then clamps thread_nr:

    if (thread_nr > n)
        thread_nr = n;

And shortly after evaluates:

    num_per_thread = n / thread_nr;

Does this divide by zero (0 / 0) and cause the perf tool to crash with a
fatal SIGFPE? Could we handle the n == 0 case earlier to prevent this
regression?

>  	}
>  	err = 0;
>  out_join:
> -	for (i = 0; i < thread_nr; i++)
> -		pthread_join(synthesize_threads[i], NULL);
> +	for (j = 0; j < i; j++)
> +		pthread_join(synthesize_threads[j], NULL);
>  	free(args);
>  free_threads:
>  	free(synthesize_threads);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260623053515.2677888-1-irogers@google.com?part=5