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

Ian Rogers
2025-04-07T05:01:30Z

Ensure sample reader isn't racing with events being added/removed.

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();
--
2.49.0.504.g3bcea36a83-goog