perf record: skip synthesize event when open evsel failed

[ Upstream commit 163e5f2 ]

When using perf record with the `--overwrite` option, a segmentation fault
occurs if an event fails to open. For example:

  perf record -e cycles-ct -F 1000 -a --overwrite
  Error:
  cycles-ct:H: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
  perf: Segmentation fault
      #0 0x6466b6 in dump_stack debug.c:366
      #1 0x646729 in sighandler_dump_stack debug.c:378
      #2 0x453fd1 in sigsegv_handler builtin-record.c:722
      #3 0x7f8454e65090 in __restore_rt libc-2.32.so[54090]
      #4 0x6c5671 in __perf_event__synthesize_id_index synthetic-events.c:1862
      #5 0x6c5ac0 in perf_event__synthesize_id_index synthetic-events.c:1943
      gregkh#6 0x458090 in record__synthesize builtin-record.c:2075
      gregkh#7 0x45a85a in __cmd_record builtin-record.c:2888
      gregkh#8 0x45deb6 in cmd_record builtin-record.c:4374
      gregkh#9 0x4e5e33 in run_builtin perf.c:349
      gregkh#10 0x4e60bf in handle_internal_command perf.c:401
      gregkh#11 0x4e6215 in run_argv perf.c:448
      gregkh#12 0x4e653a in main perf.c:555
      gregkh#13 0x7f8454e4fa72 in __libc_start_main libc-2.32.so[3ea72]
      gregkh#14 0x43a3ee in _start ??:0

The --overwrite option implies --tail-synthesize, which collects non-sample
events reflecting the system status when recording finishes. However, when
evsel opening fails (e.g., unsupported event 'cycles-ct'), session->evlist
is not initialized and remains NULL. The code unconditionally calls
record__synthesize() in the error path, which iterates through the NULL
evlist pointer and causes a segfault.

To fix it, move the record__synthesize() call inside the error check block, so
it's only called when there was no error during recording, ensuring that evlist
is properly initialized.

Fixes: 4ea648a ("perf record: Add --tail-synthesize option")
Signed-off-by: Shuai Xue <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: axiqia

tools/perf/builtin-record.c

@@ -2832,11 +2832,11 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 		rec->bytes_written += off_cpu_write(rec->session);
 
 	record__read_lost_samples(rec);
-	record__synthesize(rec, true);
 	/* this will be recalculated during process_buildids() */
 	rec->samples = 0;
 
 	if (!err) {
+		record__synthesize(rec, true);
 		if (!rec->timestamp_filename) {
 			record__finish_output(rec);
 		} else {