On Tue, 15 Jul 2025 14:06:50 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > > > + * Return: 0 if the callback successfully was queued.
> > > > + * UNWIND_ALREADY_PENDING if the the callback was already queued.
> > > > + * UNWIND_ALREADY_EXECUTED if the callback was already called
> > > > + * (and will not be called again)
> > > > * Negative if there's an error.
> > > > * @cookie holds the cookie of the first request by any user
> > > > */
> > >
> > > Lots of babbling in the Changelog, but no real elucidation as to why you
> > > need this second return value.
> > >
> > > AFAICT it serves no real purpose; the users of this function should not
> > > care. The only difference is that the unwind reference (your cookie)
> > > becomes a backward reference instead of a forward reference. But why
> > > would anybody care?
> >
> > Older versions of the code required it. I think I can remove it now.
>
> Ah it is still used in the perf code:
>
> perf_callchain() has:
>
> if (defer_user) {
> int ret = deferred_request(event);
> if (!ret)
> local_inc(&event->ctx->nr_no_switch_fast);
Hmm, I guess this could work if it returned non zero for both already
queued and already executed. So it doesn't need to be two different
values.
-- Steve
> else if (ret < 0)
> defer_user = false;
> }
