Re: [PATCH v4 11/16] perf intel-tpebs: Add mutex for tpebs_results

[Ian Rogers <irogers@google.com>]

On Fri, Apr 11, 2025 at 3:54 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> On Tue, Apr 08, 2025 at 11:10:38PM -0700, Ian Rogers wrote:
> > 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 f648fca17556..c5ccdbc42dc6 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;
>
> The mutex_unlock() is missing here.

Good catch, I'll fix in v5. Fwiw cleanups would have avoided this.

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > +     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
> >