Re: [RFC][PATCH 02/21] tracing: Reimplement log2

Tom Zanussi
2017-02-08T20:25:11Z

On Wed, 2017-02-08 at 15:13 -0500, Steven Rostedt wrote:
> On Wed, 8 Feb 2017 11:24:58 -0600
> Tom Zanussi <tom.zanussi@linux.intel.com> wrote:
>
> > static void destroy_hist_field(struct hist_field *hist_field)
> > {
> > + unsigned int i;
> > +
> > + if (!hist_field)
> > + return;
> > +
> > + for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++)
> > + destroy_hist_field(hist_field->operands[i]);
>
> Recursive functions get me really nervous. What limits it? Is this user
> defined? Perhaps we need to find a better way to handle this that's not
> recursive, or at least put in a hard limit of the amount it can recurse.
>

It's limited by the expression depth, which shouldn't be more than 1
deep, but you're right, there should be an explicit limit check, just in
case - will add one.

Tom

> -- Steve
>
> > +
> > kfree(hist_field);
> > }
> >
> > @@ -377,7 +393,10 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
> > }
> >
> > if (flags & HIST_FIELD_FL_LOG2) {
> > + unsigned long fl = flags & ~HIST_FIELD_FL_LOG2;
> > hist_field->fn = hist_field_log2;
> > + hist_field->operands[0] = create_hist_field(field, fl);
> > + hist_field->size = hist_field->operands[0]->size;
> > goto out;
> > }
> >
>