[PATCH v4 1/3] perf sched: Suppress latency table output when trace samples are missing

[Aaron Tomlin]

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 behavior 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, and .build_id callbacks in cmd_sched(),
and perform the trace check after event 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 | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 7fd63a9db457..fabd99a18aad 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)
@@ -2001,7 +2001,7 @@ static int perf_sched__read_events(struct perf_sched *sched)
 		.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)) {
@@ -2018,18 +2018,25 @@ static int perf_sched__read_events(struct perf_sched *sched)
 	if (perf_session__set_tracepoints_handlers(session, handlers))
 		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;
-		}
+	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];
+	err = perf_session__process_events(session);
+	if (err) {
+		pr_err("Failed to process events, error %d", err);
+		goto out_delete;
 	}
 
+	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 +5174,9 @@ 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;
 
 	argc = parse_options_subcommand(argc, argv, sched_options, sched_subcommands,
 					sched_usage, PARSE_OPT_STOP_AT_NON_OPTION);
-- 
2.55.0