Re: [PATCH v13 10/14] unwind: Clear unwind_mask on exit back to user space

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 15 Jul 2025 14:06:50 -0400
Steven Rostedt <rostedt@goodmis.org> 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;
>         }