perf record: Force ignore_missing_thread for uid option

Enable perf_evsel::ignore_missing_thread for -u option to ignore
complete failure if any of the user's processes die between its
enumeration and time we open the event.

Committer notes:

While doing a 'make -j4 allmodconfig' we sometimes get into the race:

Before:

  # perf record -u acme
  Error:
  The sys_perf_event_open() syscall returned with 3 (No such process) for event (cycles:ppp).
  /bin/dmesg may provide additional information.
  No CONFIG_PERF_EVENTS=y kernel support configured?
  #

After:

  [root@jouet ~]# perf record -u acme
  WARNING: Ignored open failure for pid 9888
  WARNING: Ignored open failure for pid 18059
  [root@jouet ~]#

Which is an improvement, with the races not preventing the remaining threads
for the specified user from being monitored, but the message probably needs
further clarification.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1481538943-21874-6-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -1687,6 +1687,9 @@ int cmd_record(int argc, const char **argv, const char *prefix __maybe_unused)
 		goto out;
 	}
 
+	/* Enable ignoring missing threads when -u option is defined. */
+	rec->opts.ignore_missing_thread = rec->opts.target.uid != UINT_MAX;
+
 	err = -ENOMEM;
 	if (perf_evlist__create_maps(rec->evlist, &rec->opts.target) < 0)
 		usage_with_options(record_usage, record_options);