Re: [PATCH v2 11/16] perf intel-tpebs: Add mutex for tpebs_results

Liang, Kan
2025-04-07T19:49:41Z

On 2025-04-07 1:00 a.m., Ian Rogers wrote:
> Ensure sample reader isn't racing with events being added/removed.

Is it a bug fix?

I think the tpebs have been merged for a while. Should the backport be
required?

Thanks,
Kan>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/intel-tpebs.c | 51 ++++++++++++++++++++++++++++++-----
> 1 file changed, 44 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/intel-tpebs.c b/tools/perf/util/intel-tpebs.c
> index 452ce3698221..29616d087bce 100644
> --- a/tools/perf/util/intel-tpebs.c
> +++ b/tools/perf/util/intel-tpebs.c
> @@ -16,6 +16,7 @@
> #include "debug.h"
> #include "evlist.h"
> #include "evsel.h"
> +#include "mutex.h"
> #include "session.h"
> #include "tool.h"
> #include "cpumap.h"
> @@ -32,6 +33,7 @@ bool tpebs_recording;
> static LIST_HEAD(tpebs_results);
> static pthread_t tpebs_reader_thread;
> static struct child_process tpebs_cmd;
> +static struct mutex tpebs_mtx;
>
> struct tpebs_retire_lat {
> struct list_head nd;
> @@ -51,6 +53,19 @@ struct tpebs_retire_lat {
>
> static struct tpebs_retire_lat *tpebs_retire_lat__find(struct evsel *evsel);
>
> +static void tpebs_mtx_init(void)
> +{
> + mutex_init(&tpebs_mtx);
> +}
> +
> +static struct mutex *tpebs_mtx_get(void)
> +{
> + static pthread_once_t tpebs_mtx_once = PTHREAD_ONCE_INIT;
> +
> + pthread_once(&tpebs_mtx_once, tpebs_mtx_init);
> + return &tpebs_mtx;
> +}
> +
> static int evsel__tpebs_start_perf_record(struct evsel *evsel, int control_fd[], int ack_fd[])
> {
> const char **record_argv;
> @@ -59,13 +74,15 @@ static int evsel__tpebs_start_perf_record(struct evsel *evsel, int control_fd[],
> char cpumap_buf[50];
> struct tpebs_retire_lat *t;
>
> + mutex_lock(tpebs_mtx_get());
> list_for_each_entry(t, &tpebs_results, nd)
> tpebs_event_size++;
>
> record_argv = malloc((10 + 2 * tpebs_event_size) * sizeof(*record_argv));
> - if (!record_argv)
> + if (!record_argv) {
> + mutex_unlock(tpebs_mtx_get());
> return -ENOMEM;
> -
> + }
> record_argv[i++] = "perf";
> record_argv[i++] = "record";
> record_argv[i++] = "-W";
> @@ -101,6 +118,7 @@ static int evsel__tpebs_start_perf_record(struct evsel *evsel, int control_fd[],
> list_for_each_entry(t, &tpebs_results, nd)
> t->started = true;
>
> + mutex_unlock(tpebs_mtx_get());
> return ret;
> }
>
> @@ -112,9 +130,12 @@ static int process_sample_event(const struct perf_tool *tool __maybe_unused,
> {
> struct tpebs_retire_lat *t;
>
> + mutex_lock(tpebs_mtx_get());
> t = tpebs_retire_lat__find(evsel);
> - if (!t)
> + if (!t) {
> + mutex_unlock(tpebs_mtx_get());
> return -EINVAL;
> + }
> /*
> * Need to handle per core results? We are assuming average retire
> * latency value will be used. Save the number of samples and the sum of
> @@ -123,6 +144,7 @@ static int process_sample_event(const struct perf_tool *tool __maybe_unused,
> t->count += 1;
> t->sum += sample->retire_lat;
> t->val = (double) t->sum / t->count;
> + mutex_unlock(tpebs_mtx_get());
> return 0;
> }
>
> @@ -229,7 +251,6 @@ static struct tpebs_retire_lat *tpebs_retire_lat__new(struct evsel *evsel)
> return NULL;
> }
> result->evsel = evsel;
> - list_add_tail(&result->nd, &tpebs_results);
> return result;
> }
>
> @@ -282,16 +303,22 @@ static struct tpebs_retire_lat *tpebs_retire_lat__find(struct evsel *evsel)
> static int evsel__tpebs_prepare(struct evsel *evsel)
> {
> struct evsel *pos;
> - struct tpebs_retire_lat *tpebs_event = tpebs_retire_lat__find(evsel);
> + struct tpebs_retire_lat *tpebs_event;
>
> + mutex_lock(tpebs_mtx_get());
> + tpebs_event = tpebs_retire_lat__find(evsel);
> if (tpebs_event) {
> /* evsel, or an identically named one, was already prepared. */
> + mutex_unlock(tpebs_mtx_get());
> return 0;
> }
> tpebs_event = tpebs_retire_lat__new(evsel);
> if (!tpebs_event)
> return -ENOMEM;
>
> + list_add_tail(&tpebs_event->nd, &tpebs_results);
> + mutex_unlock(tpebs_mtx_get());
> +
> /*
> * Eagerly prepare all other evsels on the list to try to ensure that by
> * open they are all known.
> @@ -317,6 +344,7 @@ static int evsel__tpebs_prepare(struct evsel *evsel)
> int evsel__tpebs_open(struct evsel *evsel)
> {
> int ret;
> + bool tpebs_empty;
>
> /* We should only run tpebs_start when tpebs_recording is enabled. */
> if (!tpebs_recording)
> @@ -336,7 +364,10 @@ int evsel__tpebs_open(struct evsel *evsel)
> if (ret)
> return ret;
>
> - if (!list_empty(&tpebs_results)) {
> + mutex_lock(tpebs_mtx_get());
> + tpebs_empty = list_empty(&tpebs_results);
> + mutex_unlock(tpebs_mtx_get());
> + if (!tpebs_empty) {
> struct pollfd pollfd = { .events = POLLIN, };
> int control_fd[2], ack_fd[2], len;
> char ack_buf[8];
> @@ -436,8 +467,10 @@ int evsel__tpebs_read(struct evsel *evsel, int cpu_map_idx, int thread)
> */
> tpebs_stop();
>
> + mutex_lock(tpebs_mtx_get());
> t = tpebs_retire_lat__find(evsel);
> val = rint(t->val);
> + mutex_unlock(tpebs_mtx_get());
>
> if (old_count) {
> count->val = old_count->val + val;
> @@ -460,9 +493,13 @@ int evsel__tpebs_read(struct evsel *evsel, int cpu_map_idx, int thread)
> */
> void evsel__tpebs_close(struct evsel *evsel)
> {
> - struct tpebs_retire_lat *t = tpebs_retire_lat__find(evsel);
> + struct tpebs_retire_lat *t;
>
> + mutex_lock(tpebs_mtx_get());
> + t = tpebs_retire_lat__find(evsel);
> + list_del_init(&t->nd);
> tpebs_retire_lat__delete(t);
> + mutex_unlock(tpebs_mtx_get());
>
> if (list_empty(&tpebs_results))
> tpebs_stop();