Re: [PATCH 18/32] tracing: Add simple expression support to hist triggers

Namhyung Kim
2017-07-21T02:03:16Z

Hi Tom,

On Mon, Jun 26, 2017 at 05:49:19PM -0500, Tom Zanussi wrote:
> Add support for simple addition, subtraction, and unary expressions
> (-(expr) and expr, where expr = b-a, a+b, a+b+c) to hist triggers, in
> order to support a minimal set of useful inter-event calculations.
>
> These operations are needed for calculating latencies between events
> (timestamp1-timestamp0) and for combined latencies (latencies over 3
> or more events).
>
> In the process, factor out some common code from key and value
> parsing.
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> ---

[SNIP]
> +static char *expr_str(struct hist_field *field, unsigned int level)
> +{
> + char *expr = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
> +
> + if (!expr || level > 1)
> + return NULL;

Looks like a memory leak.

[SNIP]
> +static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> + struct trace_event_file *file,
> + char *str, unsigned long flags,
> + char *var_name, unsigned int level)
> +{
> + struct hist_field *operand1 = NULL, *operand2 = NULL, *expr = NULL;
> + unsigned long operand_flags;
> + int field_op, ret = -EINVAL;
> + char *sep, *operand1_str;
> +
> + if (level > 2)
> + return NULL;
> +
> + field_op = contains_operator(str);
> + if (field_op == FIELD_OP_NONE)
> + return NULL;

Why not calling parse_atom() here? It'd make the code simpler IMHO.

Thanks,
Namhyung

> +
> + if (field_op == FIELD_OP_UNARY_MINUS)
> + return parse_unary(hist_data, file, str, flags, var_name, ++level);
> +
> + switch (field_op) {
> + case FIELD_OP_MINUS:
> + sep = "-";
> + break;
> + case FIELD_OP_PLUS:
> + sep = "+";
> + break;
> + default:
> + goto free;
> + }
> +
> + operand1_str = strsep(&str, sep);
> + if (!operand1_str || !str)
> + goto free;
> +
> + operand_flags = 0;
> + operand1 = parse_atom(hist_data, file, operand1_str,
> + &operand_flags, NULL);
> + if (IS_ERR(operand1)) {
> + ret = PTR_ERR(operand1);
> + operand1 = NULL;
> + goto free;
> + }
> +
> + // rest of string could be another expression e.g. b+c in a+b+c
> + operand_flags = 0;
> + operand2 = parse_expr(hist_data, file, str, operand_flags, NULL, ++level);
> + if (IS_ERR(operand2)) {
> + ret = PTR_ERR(operand2);
> + operand2 = NULL;
> + goto free;
> + }
> + if (!operand2) {
> + operand_flags = 0;
> + operand2 = parse_atom(hist_data, file, str,
> + &operand_flags, NULL);
> + if (IS_ERR(operand2)) {
> + ret = PTR_ERR(operand2);
> + operand2 = NULL;
> + goto free;
> + }
> + }
> +
> + flags |= HIST_FIELD_FL_EXPR;
> + expr = create_hist_field(hist_data, NULL, flags, var_name);
> + if (!expr) {
> + ret = -ENOMEM;
> + goto free;
> + }
> +
> + expr->operands[0] = operand1;
> + expr->operands[1] = operand2;
> + expr->operator = field_op;
> + expr->name = expr_str(expr, 0);
> +
> + switch (field_op) {
> + case FIELD_OP_MINUS:
> + expr->fn = hist_field_minus;
> + break;
> + case FIELD_OP_PLUS:
> + expr->fn = hist_field_plus;
> + break;
> + default:
> + goto free;
> + }
> +
> + return expr;
> + free:
> + destroy_hist_field(operand1, 0);
> + destroy_hist_field(operand2, 0);
> + destroy_hist_field(expr, 0);
> +
> + return ERR_PTR(ret);
> +}