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SubjectRe: [PATCH v2 27/40] tracing: Add support for 'synthetic' events
On Tue,  5 Sep 2017 16:57:39 -0500
Tom Zanussi <tom.zanussi@linux.intel.com> wrote:


> +static int synth_field_string_size(char *type)
> +{
> + char buf[4], *end, *start;
> + unsigned int len;
> + int size, err;
> +
> + start = strstr(type, "char[");
> + if (start == NULL)
> + return -EINVAL;
> + start += strlen("char[");
> +
> + end = strchr(type, ']');
> + if (!end || end < start)
> + return -EINVAL;
> +
> + len = end - start;
> + if (len > 2)

Is there a reason for max of 2? Could it be 3?

> + return -EINVAL;
> +
> + strncpy(buf, start, len);
> + buf[len] = '\0';

With len=3, buf[len] would be the 4th byte, which buf is defined to be.

> +
> + err = kstrtouint(buf, 0, &size);
> + if (err)
> + return err;
> +
> + if (size > STR_VAR_LEN_MAX)
> + return -EINVAL;
> +
> + return size;
> +}
> +
> +static int synth_field_size(char *type)
> +{
> + int size = 0;
> +
> + if (strcmp(type, "s64") == 0)
> + size = sizeof(s64);
> + else if (strcmp(type, "u64") == 0)
> + size = sizeof(u64);
> + else if (strcmp(type, "s32") == 0)
> + size = sizeof(s32);
> + else if (strcmp(type, "u32") == 0)
> + size = sizeof(u32);
> + else if (strcmp(type, "s16") == 0)
> + size = sizeof(s16);
> + else if (strcmp(type, "u16") == 0)
> + size = sizeof(u16);
> + else if (strcmp(type, "s8") == 0)
> + size = sizeof(s8);
> + else if (strcmp(type, "u8") == 0)
> + size = sizeof(u8);
> + else if (strcmp(type, "char") == 0)
> + size = sizeof(char);
> + else if (strcmp(type, "unsigned char") == 0)
> + size = sizeof(unsigned char);
> + else if (strcmp(type, "int") == 0)
> + size = sizeof(int);
> + else if (strcmp(type, "unsigned int") == 0)
> + size = sizeof(unsigned int);
> + else if (strcmp(type, "long") == 0)
> + size = sizeof(long);
> + else if (strcmp(type, "unsigned long") == 0)
> + size = sizeof(unsigned long);
> + else if (strcmp(type, "pid_t") == 0)
> + size = sizeof(pid_t);
> + else if (synth_field_is_string(type))
> + size = synth_field_string_size(type);
> +
> + return size;
> +}
> +
> +static const char *synth_field_fmt(char *type)
> +{
> + const char *fmt = "%llu";
> +
> + if (strcmp(type, "s64") == 0)
> + fmt = "%lld";
> + else if (strcmp(type, "u64") == 0)
> + fmt = "%llu";
> + else if (strcmp(type, "s32") == 0)
> + fmt = "%d";
> + else if (strcmp(type, "u32") == 0)
> + fmt = "%u";
> + else if (strcmp(type, "s16") == 0)
> + fmt = "%d";
> + else if (strcmp(type, "u16") == 0)
> + fmt = "%u";
> + else if (strcmp(type, "s8") == 0)
> + fmt = "%d";
> + else if (strcmp(type, "u8") == 0)
> + fmt = "%u";
> + else if (strcmp(type, "char") == 0)
> + fmt = "%d";
> + else if (strcmp(type, "unsigned char") == 0)
> + fmt = "%u";
> + else if (strcmp(type, "int") == 0)
> + fmt = "%d";
> + else if (strcmp(type, "unsigned int") == 0)
> + fmt = "%u";
> + else if (strcmp(type, "long") == 0)
> + fmt = "%ld";
> + else if (strcmp(type, "unsigned long") == 0)
> + fmt = "%lu";
> + else if (strcmp(type, "pid_t") == 0)
> + fmt = "%d";
> + else if (strstr(type, "[") == 0)
> + fmt = "%s";
> +
> + return fmt;
> +}
> +
> +static enum print_line_t print_synth_event(struct trace_iterator *iter,
> + int flags,
> + struct trace_event *event)
> +{
> + struct trace_array *tr = iter->tr;
> + struct trace_seq *s = &iter->seq;
> + struct synth_trace_event *entry;
> + struct synth_event *se;
> + unsigned int i, n_u64;
> + char print_fmt[32];
> + const char *fmt;
> +
> + entry = (struct synth_trace_event *)iter->ent;
> + se = container_of(event, struct synth_event, call.event);
> +
> + trace_seq_printf(s, "%s: ", se->name);
> +
> + for (i = 0, n_u64 = 0; i < se->n_fields; i++) {
> + if (trace_seq_has_overflowed(s))
> + goto end;
> +
> + fmt = synth_field_fmt(se->fields[i]->type);
> +
> + /* parameter types */
> + if (tr->trace_flags & TRACE_ITER_VERBOSE)
> + trace_seq_printf(s, "%s ", fmt);
> +
> + sprintf(print_fmt, "%%s=%s%%s", fmt);

Please use snprintf().

> +
> + /* parameter values */
> + if (se->fields[i]->is_string) {
> + trace_seq_printf(s, print_fmt, se->fields[i]->name,
> + (char *)entry->fields[n_u64],
> + i == se->n_fields - 1 ? "" : " ");
> + n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
> + } else {
> + trace_seq_printf(s, print_fmt, se->fields[i]->name,
> + entry->fields[n_u64],
> + i == se->n_fields - 1 ? "" : " ");
> + n_u64++;
> + }
> + }
> +end:
> + trace_seq_putc(s, '\n');
> +
> + return trace_handle_return(s);
> +}
> +
> +static struct trace_event_functions synth_event_funcs = {
> + .trace = print_synth_event
> +};
> +
> +static notrace void trace_event_raw_event_synth(void *__data,
> + u64 *var_ref_vals,
> + unsigned int var_ref_idx)
> +{
> + struct trace_event_file *trace_file = __data;
> + struct synth_trace_event *entry;
> + struct trace_event_buffer fbuffer;
> + struct synth_event *event;
> + unsigned int i, n_u64;
> + int fields_size = 0;
> +
> + event = trace_file->event_call->data;
> +
> + if (trace_trigger_soft_disabled(trace_file))
> + return;
> +
> + fields_size = event->n_u64 * sizeof(u64);
> +
> + entry = trace_event_buffer_reserve(&fbuffer, trace_file,
> + sizeof(*entry) + fields_size);
> + if (!entry)
> + return;
> +
> + for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
> + if (event->fields[i]->is_string) {
> + char *str_val = (char *)var_ref_vals[var_ref_idx + i];
> + char *str_field = (char *)&entry->fields[n_u64];
> +
> + strncpy(str_field, str_val, STR_VAR_LEN_MAX);
> + n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
> + } else {
> + entry->fields[i] = var_ref_vals[var_ref_idx + i];
> + n_u64++;
> + }
> + }
> +
> + trace_event_buffer_commit(&fbuffer);
> +}
> +
> +static void free_synth_event_print_fmt(struct trace_event_call *call)
> +{
> + if (call)
> + kfree(call->print_fmt);

For safety reasons should this be:

if (call) {
kfree(call->print_fmt);
call->print_fmt = NULL;
}
?

> +}
> +
> +static int __set_synth_event_print_fmt(struct synth_event *event,
> + char *buf, int len)
> +{
> + const char *fmt;
> + int pos = 0;
> + int i;
> +
> + /* When len=0, we just calculate the needed length */
> +#define LEN_OR_ZERO (len ? len - pos : 0)
> +
> + pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");
> + for (i = 0; i < event->n_fields; i++) {
> + fmt = synth_field_fmt(event->fields[i]->type);
> + pos += snprintf(buf + pos, LEN_OR_ZERO, "%s=%s%s",
> + event->fields[i]->name, fmt,
> + i == event->n_fields - 1 ? "" : ", ");
> + }
> + pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");
> +
> + for (i = 0; i < event->n_fields; i++) {
> + pos += snprintf(buf + pos, LEN_OR_ZERO,
> + ", REC->%s", event->fields[i]->name);
> + }
> +
> +#undef LEN_OR_ZERO
> +
> + /* return the length of print_fmt */
> + return pos;
> +}
> +
> +static int set_synth_event_print_fmt(struct trace_event_call *call)
> +{
> + struct synth_event *event = call->data;
> + char *print_fmt;
> + int len;
> +
> + /* First: called with 0 length to calculate the needed length */
> + len = __set_synth_event_print_fmt(event, NULL, 0);
> +
> + print_fmt = kmalloc(len + 1, GFP_KERNEL);
> + if (!print_fmt)
> + return -ENOMEM;
> +
> + /* Second: actually write the @print_fmt */
> + __set_synth_event_print_fmt(event, print_fmt, len + 1);
> + call->print_fmt = print_fmt;
> +
> + return 0;
> +}
> +
> +static void free_synth_field(struct synth_field *field)
> +{
> + kfree(field->type);
> + kfree(field->name);
> + kfree(field);
> +}
> +
> +static struct synth_field *parse_synth_field(char *field_type,
> + char *field_name)
> +{
> + struct synth_field *field;
> + int len, ret = 0;
> + char *array;
> +
> + if (field_type[0] == ';')
> + field_type++;
> +
> + len = strlen(field_name);
> + if (field_name[len - 1] == ';')
> + field_name[len - 1] = '\0';
> +
> + field = kzalloc(sizeof(*field), GFP_KERNEL);
> + if (!field)
> + return ERR_PTR(-ENOMEM);
> +
> + len = strlen(field_type) + 1;
> + array = strchr(field_name, '[');
> + if (array)
> + len += strlen(array);
> + field->type = kzalloc(len, GFP_KERNEL);
> + if (!field->type) {
> + ret = -ENOMEM;
> + goto free;
> + }
> + strcat(field->type, field_type);
> + if (array) {
> + strcat(field->type, array);
> + *array = '\0';
> + }
> +
> + field->size = synth_field_size(field->type);
> + if (!field->size) {
> + ret = -EINVAL;
> + goto free;
> + }
> +
> + if (synth_field_is_string(field->type))
> + field->is_string = true;
> +
> + field->is_signed = synth_field_signed(field->type);
> +
> + field->name = kstrdup(field_name, GFP_KERNEL);
> + if (!field->name) {
> + ret = -ENOMEM;
> + goto free;
> + }
> + out:
> + return field;
> + free:
> + free_synth_field(field);
> + field = ERR_PTR(ret);
> + goto out;
> +}
> +
> +static void free_synth_tracepoint(struct tracepoint *tp)
> +{
> + if (!tp)
> + return;
> +
> + kfree(tp->name);
> + kfree(tp);
> +}
> +
> +static struct tracepoint *alloc_synth_tracepoint(char *name)
> +{
> + struct tracepoint *tp;
> + int ret = 0;
> +
> + tp = kzalloc(sizeof(*tp), GFP_KERNEL);
> + if (!tp) {
> + ret = -ENOMEM;
> + goto free;

Why the goto free here? It's the first allocation. Should just be able
to return ERR_PTR(-ENOMEM).

> + }
> +
> + tp->name = kstrdup(name, GFP_KERNEL);
> + if (!tp->name) {
> + ret = -ENOMEM;
> + goto free;

Then we don't even need the goto. Just free free tp, and return with
error.

> + }
> +
> + tp->dynamic = true;
> +
> + return tp;
> + free:
> + free_synth_tracepoint(tp);
> +
> + return ERR_PTR(ret);
> +}
> +
> +typedef void (*synth_probe_func_t) (void *__data, u64 *var_ref_vals,
> + unsigned int var_ref_idx);
> +
> +static inline void trace_synth(struct synth_event *event, u64 *var_ref_vals,
> + unsigned int var_ref_idx)
> +{
> + struct tracepoint *tp = event->tp;
> +
> + if (unlikely(atomic_read(&tp->key.enabled) > 0)) {
> + struct tracepoint_func *probe_func_ptr;
> + synth_probe_func_t probe_func;
> + void *__data;
> +
> + if (!(cpu_online(raw_smp_processor_id())))
> + return;
> +
> + probe_func_ptr = rcu_dereference_sched((tp)->funcs);
> + if (probe_func_ptr) {
> + do {
> + probe_func = (probe_func_ptr)->func;
> + __data = (probe_func_ptr)->data;

Are the parenthesis around probe_func_ptr required?

> + probe_func(__data, var_ref_vals, var_ref_idx);
> + } while ((++probe_func_ptr)->func);
> + }
> + }
> +}
> +
> +static struct synth_event *find_synth_event(const char *name)
> +{
> + struct synth_event *event;
> +
> + list_for_each_entry(event, &synth_event_list, list) {
> + if (strcmp(event->name, name) == 0)
> + return event;
> + }
> +
> + return NULL;
> +}
> +
> +static int register_synth_event(struct synth_event *event)
> +{
> + struct trace_event_call *call = &event->call;
> + int ret = 0;
> +
> + event->call.class = &event->class;
> + event->class.system = kstrdup(SYNTH_SYSTEM, GFP_KERNEL);
> + if (!event->class.system) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + event->tp = alloc_synth_tracepoint(event->name);
> + if (IS_ERR(event->tp)) {
> + ret = PTR_ERR(event->tp);
> + event->tp = NULL;
> + goto out;
> + }
> +
> + INIT_LIST_HEAD(&call->class->fields);
> + call->event.funcs = &synth_event_funcs;
> + call->class->define_fields = synth_event_define_fields;
> +
> + ret = register_trace_event(&call->event);
> + if (!ret) {
> + ret = -ENODEV;
> + goto out;
> + }
> + call->flags = TRACE_EVENT_FL_TRACEPOINT;
> + call->class->reg = trace_event_reg;
> + call->class->probe = trace_event_raw_event_synth;
> + call->data = event;
> + call->tp = event->tp;
> +

Could you comment what lock inversion is being avoided by the releasing
of this mutex.

> + mutex_unlock(&synth_event_mutex);

Please add a comment before this function that states that this
function releases synth_event_mutex.

> + ret = trace_add_event_call(call);
> + mutex_lock(&synth_event_mutex);
> + if (ret) {
> + pr_warn("Failed to register synthetic event: %s\n",
> + trace_event_name(call));
> + goto err;
> + }
> +
> + ret = set_synth_event_print_fmt(call);
> + if (ret < 0) {
> + mutex_unlock(&synth_event_mutex);
> + trace_remove_event_call(call);
> + mutex_lock(&synth_event_mutex);
> + goto err;
> + }
> + out:
> + return ret;
> + err:
> + unregister_trace_event(&call->event);
> + goto out;
> +}
> +
> +static int unregister_synth_event(struct synth_event *event)
> +{
> + struct trace_event_call *call = &event->call;
> + int ret;
> +
> + mutex_unlock(&synth_event_mutex);

Same here.

> + ret = trace_remove_event_call(call);
> + mutex_lock(&synth_event_mutex);
> + if (ret) {
> + pr_warn("Failed to remove synthetic event: %s\n",
> + trace_event_name(call));
> + free_synth_event_print_fmt(call);

Is it safe to call unregister_trace_event() with the synth_event_mutex
held?

> + unregister_trace_event(&call->event);
> + }
> +
> + return ret;
> +}
> +
> +static void remove_synth_event(struct synth_event *event)
> +{
> + unregister_synth_event(event);
> + list_del(&event->list);
> +}
> +
> +static int add_synth_event(struct synth_event *event)
> +{
> + int ret;
> +
> + ret = register_synth_event(event);
> + if (ret)
> + return ret;
> +
> + list_add(&event->list, &synth_event_list);
> +
> + return 0;
> +}
> +
> +static void free_synth_event(struct synth_event *event)
> +{
> + unsigned int i;
> +
> + if (!event)
> + return;
> +
> + for (i = 0; i < event->n_fields; i++)
> + free_synth_field(event->fields[i]);
> +
> + kfree(event->fields);
> + kfree(event->name);
> + kfree(event->class.system);
> + free_synth_tracepoint(event->tp);
> + free_synth_event_print_fmt(&event->call);
> + kfree(event);
> +}
> +
> +static struct synth_event *alloc_synth_event(char *event_name, int n_fields,
> + struct synth_field **fields)
> +{
> + struct synth_event *event;
> + unsigned int i;
> +
> + event = kzalloc(sizeof(*event), GFP_KERNEL);
> + if (!event) {
> + event = ERR_PTR(-ENOMEM);
> + goto out;
> + }
> +
> + event->name = kstrdup(event_name, GFP_KERNEL);
> + if (!event->name) {
> + kfree(event);
> + event = ERR_PTR(-ENOMEM);
> + goto out;
> + }
> +
> + event->fields = kcalloc(n_fields, sizeof(event->fields), GFP_KERNEL);
> + if (!event->fields) {
> + free_synth_event(event);
> + event = ERR_PTR(-ENOMEM);
> + goto out;

Interesting error handling process. I'm fine with keeping this.

> + }
> +
> + for (i = 0; i < n_fields; i++)
> + event->fields[i] = fields[i];
> +
> + event->n_fields = n_fields;
> + out:
> + return event;
> +}
> +
> +static int create_synth_event(int argc, char **argv)
> +{
> + struct synth_field *field, *fields[SYNTH_FIELDS_MAX];
> + struct synth_event *event = NULL;
> + bool delete_event = false;
> + int i, n_fields = 0, ret = 0;
> + char *name;
> +
> + mutex_lock(&synth_event_mutex);
> +
> + /*
> + * Argument syntax:
> + * - Add synthetic event: <event_name> field[;field] ...
> + * - Remove synthetic event: !<event_name> field[;field] ...
> + * where 'field' = type field_name
> + */
> + if (argc < 1) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + name = argv[0];
> + if (name[0] == '!') {
> + delete_event = true;
> + name++;
> + }
> +
> + event = find_synth_event(name);
> + if (event) {
> + if (delete_event) {
> + if (event->ref) {
> + ret = -EBUSY;
> + goto out;
> + }
> + remove_synth_event(event);
> + free_synth_event(event);
> + goto out;
> + }
> + ret = -EEXIST;
> + goto out;
> + } else if (delete_event) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + if (argc < 2) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + for (i = 1; i < argc - 1; i++) {
> + if (strcmp(argv[i], ";") == 0)
> + continue;
> + if (n_fields == SYNTH_FIELDS_MAX) {
> + ret = -EINVAL;
> + goto err;
> + }
> +
> + field = parse_synth_field(argv[i], argv[i + 1]);
> + if (IS_ERR(field)) {
> + ret = PTR_ERR(field);
> + goto err;
> + }
> + fields[n_fields] = field;
> + i++; n_fields++;
> + }
> +
> + if (i < argc) {
> + ret = -EINVAL;
> + goto err;
> + }
> +
> + event = alloc_synth_event(name, n_fields, fields);
> + if (IS_ERR(event)) {
> + ret = PTR_ERR(event);
> + event = NULL;
> + goto err;
> + }
> +

Add comment that the synth_event_mutex is released by this function.

> + add_synth_event(event);
> + out:
> + mutex_unlock(&synth_event_mutex);
> +
> + return ret;
> + err:
> + for (i = 0; i < n_fields; i++)
> + free_synth_field(fields[i]);
> + free_synth_event(event);
> +
> + goto out;
> +}
> +
> +static int release_all_synth_events(void)
> +{
> + struct synth_event *event, *e;
> + int ret = 0;
> +
> + mutex_lock(&synth_event_mutex);
> +
> + list_for_each_entry(event, &synth_event_list, list) {
> + if (event->ref) {
> + ret = -EBUSY;
> + goto out;
> + }
> + }
> +
> + list_for_each_entry_safe(event, e, &synth_event_list, list) {

Same here.

-- Steve

> + remove_synth_event(event);
> + free_synth_event(event);
> + }
> + out:
> + mutex_unlock(&synth_event_mutex);
> +
> + return ret;
> +}

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