OOM detection on cgroup v2 not always working

[kolyshkin]

Continuing the investigation that started in cri-o/cri-o#6973

Apparently, sometimes systemd removes the cgroup before conmon can read its memory.events. I don't have any ideas about how to work around that race (in conmon; that is).

Another small issue I found is sometimes OOM can be misdetected because the code use the same static counter variable for both oom and oom_kill, which appears to be wrong.

conmon/src/cgroup.c

Lines 269 to 310 in ebc6717

	gboolean check_cgroup2_oom()
	{
	static long int last_counter = 0;
	if (!is_cgroup_v2)
	return G_SOURCE_REMOVE;
	_cleanup_free_ char *memory_events_file_path = g_build_filename(cgroup2_path, "memory.events", NULL);
	_cleanup_fclose_ FILE *fp = fopen(memory_events_file_path, "re");
	if (fp == NULL) {
	nwarnf("Failed to open cgroups file: %s", memory_events_file_path);
	return G_SOURCE_CONTINUE;
	}
	_cleanup_free_ char *line = NULL;
	size_t len = 0;
	ssize_t read;
	while ((read = getline(&line, &len, fp)) != -1) {
	long int counter;
	const int oom_len = 4, oom_kill_len = 9;
	if (read >= oom_kill_len + 2 && memcmp(line, "oom_kill ", oom_kill_len) == 0)
	len = oom_kill_len;
	else if (read >= oom_len + 2 && memcmp(line, "oom ", oom_len) == 0)
	len = oom_len;
	else
	continue;
	counter = strtol(&line[len], NULL, 10);
	if (counter == LONG_MAX) {
	nwarnf("Failed to parse: %s", &line[len]);
	continue;
	}
	if (counter == 0)
	continue;
	if (counter != last_counter) {
	if (write_oom_files() == 0)
	last_counter = counter;