perf evsel: Always preserve errno while cleaning up perf_event_open failures

In some cases when perf_event_open fails, it may do some closes to clean
up. In special cases these closes can fail too, which overwrites the
errno of the perf_event_open, which is then incorrectly reported.

Save/restore errno around closes.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20191020175202.32456-2-andi@firstfloor.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -1574,7 +1574,7 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
 {
 	int cpu, thread, nthreads;
 	unsigned long flags = PERF_FLAG_FD_CLOEXEC;
-	int pid = -1, err;
+	int pid = -1, err, old_errno;
 	enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;
 
 	if ((perf_missing_features.write_backward && evsel->core.attr.write_backward) ||
@@ -1727,8 +1727,8 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
 	 */
 	if (err == -EMFILE && set_rlimit < INCREASED_MAX) {
 		struct rlimit l;
-		int old_errno = errno;
 
+		old_errno = errno;
 		if (getrlimit(RLIMIT_NOFILE, &l) == 0) {
 			if (set_rlimit == NO_CHANGE)
 				l.rlim_cur = l.rlim_max;
@@ -1812,6 +1812,7 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
 	if (err)
 		threads->err_thread = thread;
 
+	old_errno = errno;
 	do {
 		while (--thread >= 0) {
 			close(FD(evsel, cpu, thread));
@@ -1819,6 +1820,7 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
 		}
 		thread = nthreads;
 	} while (--cpu >= 0);
+	errno = old_errno;
 	return err;
 }