perf intel-tpebs: Avoid race when evlist is being deleted

Reading through the evsel->evlist may seg fault if a sample arrives
when the evlist is being deleted.

Detect this case and ignore samples arriving when the evlist is being
deleted.

Fixes: bcfab08 ("perf intel-tpebs: Filter non-workload samples")
Signed-off-by: Ian Rogers <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alex Gaynor <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andreas Hindborg <[email protected]>
Cc: Benno Lossin <[email protected]>
Cc: Björn Roy Baron <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: Dmitriy Vyukov <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: Howard Chu <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiapeng Chong <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephen Brennan <[email protected]>
Cc: Trevor Gross <[email protected]>
Cc: Weilin Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: captain5050

tools/perf/util/intel-tpebs.c

@@ -162,9 +162,17 @@ static bool is_child_pid(pid_t parent, pid_t child)
 
 static bool should_ignore_sample(const struct perf_sample *sample, const struct tpebs_retire_lat *t)
 {
-	pid_t workload_pid = t->evsel->evlist->workload.pid;
-	pid_t sample_pid = sample->pid;
+	pid_t workload_pid, sample_pid = sample->pid;
 
+	/*
+	 * During evlist__purge the evlist will be removed prior to the
+	 * evsel__exit calling evsel__tpebs_close and taking the
+	 * tpebs_mtx. Avoid a segfault by ignoring samples in this case.
+	 */
+	if (t->evsel->evlist == NULL)
+		return true;
+
+	workload_pid = t->evsel->evlist->workload.pid;
 	if (workload_pid < 0 || workload_pid == sample_pid)
 		return false;