[PATCH v5 1/3] perf sched: Suppress latency table output when trace samples are missing
From: Aaron Tomlin
Date: Thu Jul 30 2026 - 14:58:17 EST
When 'perf sched latency' is executed on a perf.data file that lacks
tracepoint samples (i.e., a file recorded without the -R flag or
containing only non-tracepoint events), perf_session__has_traces()
correctly outputs an error message. However, perf_sched__read_events()
subsequently falls through and returns 0 (success).
Consequently, caller functions such as perf_sched__lat() assume event
processing succeeded and proceed to render empty latency header tables
and total summary statistics.
Fix this behaviour by ensuring perf_sched__read_events() aborts early and
returns a suitable error code when perf_session__has_traces() evaluates
to false.
For pipe mode streams, event attributes are received dynamically during
event processing, meaning session->evlist is not populated prior to
perf_session__process_events(). To handle pipe input correctly:
- Register the missing .attr, .tracing_data, .build_id, and .feature
callbacks in cmd_sched()
- Promote the handlers array to file-scope (latency_handlers[]) and
invoke evlist__set_tracepoints_handlers() dynamically inside
perf_sched__process_tracepoint_sample() when evsel->handler is NULL
- Perform the trace check post-processing when handling pipe data
Additionally, validate thread__get_runtime() against NULL in
map_switch_event() to prevent potential null-pointer dereferences.
Fixes: 27295592c22e ("perf session: Share the common trace sample_check routine as perf_session__has_traces")
Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxxx>
---
tools/perf/builtin-sched.c | 68 +++++++++++++++++++++++++-------------
1 file changed, 45 insertions(+), 23 deletions(-)
diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 7fd63a9db457..0abf9f1f3c2e 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -1833,7 +1833,7 @@ static int map_switch_event(struct perf_sched *sched, struct perf_sample *sampl
sched_out:
if (sched->map.task_name) {
tr = thread__get_runtime(sched->curr_out_thread[this_cpu.cpu]);
- if (strcmp(tr->shortname, "") == 0)
+ if (tr == NULL || strcmp(tr->shortname, "") == 0)
goto out;
if (proceed == 1)
@@ -1938,6 +1938,15 @@ typedef int (*tracepoint_handler)(const struct perf_tool *tool,
struct perf_sample *sample,
struct machine *machine);
+static struct evsel_str_handler latency_handlers[] = {
+ { "sched:sched_switch", process_sched_switch_event, },
+ { "sched:sched_stat_runtime", process_sched_runtime_event, },
+ { "sched:sched_wakeup", process_sched_wakeup_event, },
+ { "sched:sched_waking", process_sched_wakeup_event, },
+ { "sched:sched_wakeup_new", process_sched_wakeup_event, },
+ { "sched:sched_migrate_task", process_sched_migrate_task_event, },
+};
+
static int perf_sched__process_tracepoint_sample(const struct perf_tool *tool __maybe_unused,
union perf_event *event __maybe_unused,
struct perf_sample *sample,
@@ -1946,6 +1955,14 @@ static int perf_sched__process_tracepoint_sample(const struct perf_tool *tool __
struct evsel *evsel = sample->evsel;
int err = 0;
+ if (evsel->handler == NULL && sample->evsel->evlist) {
+ /* prefer sched_waking if it is captured */
+ if (evlist__find_tracepoint_by_name(sample->evsel->evlist, "sched:sched_waking"))
+ latency_handlers[2].handler = process_sched_wakeup_ignore;
+
+ evlist__set_tracepoints_handlers(sample->evsel->evlist, latency_handlers);
+ }
+
if (evsel->handler != NULL) {
tracepoint_handler f = evsel->handler;
err = f(tool, sample, machine);
@@ -1987,21 +2004,13 @@ static int perf_sched__process_comm(const struct perf_tool *tool __maybe_unused,
static int perf_sched__read_events(struct perf_sched *sched)
{
- struct evsel_str_handler handlers[] = {
- { "sched:sched_switch", process_sched_switch_event, },
- { "sched:sched_stat_runtime", process_sched_runtime_event, },
- { "sched:sched_wakeup", process_sched_wakeup_event, },
- { "sched:sched_waking", process_sched_wakeup_event, },
- { "sched:sched_wakeup_new", process_sched_wakeup_event, },
- { "sched:sched_migrate_task", process_sched_migrate_task_event, },
- };
struct perf_session *session;
struct perf_data data = {
.path = input_name,
.mode = PERF_DATA_MODE_READ,
.force = sched->force,
};
- int rc = -1;
+ int rc = -1, err;
session = perf_session__new(&data, &sched->tool);
if (IS_ERR(session)) {
@@ -2011,25 +2020,34 @@ static int perf_sched__read_events(struct perf_sched *sched)
symbol__init(perf_session__env(session));
- /* prefer sched_waking if it is captured */
- if (evlist__find_tracepoint_by_name(session->evlist, "sched:sched_waking"))
- handlers[2].handler = process_sched_wakeup_ignore;
+ if (!perf_data__is_pipe(session->data)) {
+ /* prefer sched_waking if it is captured */
+ if (evlist__find_tracepoint_by_name(session->evlist, "sched:sched_waking"))
+ latency_handlers[2].handler = process_sched_wakeup_ignore;
- if (perf_session__set_tracepoints_handlers(session, handlers))
+ if (perf_session__set_tracepoints_handlers(session, latency_handlers))
+ goto out_delete;
+ }
+
+ if (!perf_data__is_pipe(session->data) &&
+ !perf_session__has_traces(session, "record -R"))
goto out_delete;
- if (perf_session__has_traces(session, "record -R")) {
- int err = perf_session__process_events(session);
- if (err) {
- pr_err("Failed to process events, error %d", err);
- goto out_delete;
- }
+ err = perf_session__process_events(session);
+ if (err) {
+ pr_err("Failed to process events, error %d", err);
+ goto out_delete;
+ }
- sched->nr_events = session->evlist->stats.nr_events[0];
- sched->nr_lost_events = session->evlist->stats.total_lost;
- sched->nr_lost_chunks = session->evlist->stats.nr_events[PERF_RECORD_LOST];
+ if (perf_data__is_pipe(session->data) &&
+ !perf_session__has_traces(session, "record -R")) {
+ goto out_delete;
}
+ sched->nr_events = session->evlist->stats.nr_events[0];
+ sched->nr_lost_events = session->evlist->stats.total_lost;
+ sched->nr_lost_chunks = session->evlist->stats.nr_events[PERF_RECORD_LOST];
+
rc = 0;
out_delete:
perf_session__delete(session);
@@ -5167,6 +5185,10 @@ int cmd_sched(int argc, const char **argv)
sched.tool.namespaces = perf_event__process_namespaces;
sched.tool.lost = perf_event__process_lost;
sched.tool.fork = perf_sched__process_fork_event;
+ sched.tool.attr = perf_event__process_attr;
+ sched.tool.tracing_data = perf_event__process_tracing_data;
+ sched.tool.build_id = perf_event__process_build_id;
+ sched.tool.feature = perf_event__process_feature;
argc = parse_options_subcommand(argc, argv, sched_options, sched_subcommands,
sched_usage, PARSE_OPT_STOP_AT_NON_OPTION);
--
2.55.0