Re: [PATCHv3 1/7] uprobe: Add support for session consumer

[Jiri Olsa]

On Fri, Sep 13, 2024 at 11:32:01AM +0200, Oleg Nesterov wrote:
> On 09/13, Jiri Olsa wrote:
> >
> > On Thu, Sep 12, 2024 at 06:35:39PM +0200, Oleg Nesterov wrote:
> > > >  	list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
> > > >  				 srcu_read_lock_held(&uprobes_srcu)) {
> > > > +		/*
> > > > +		 * If we don't find return consumer, it means uprobe consumer
> > > > +		 * was added after we hit uprobe and return consumer did not
> > > > +		 * get registered in which case we call the ret_handler only
> > > > +		 * if it's not session consumer.
> > > > +		 */
> > > > +		ric = return_consumer_find(ri, &iter, uc->id);
> > > > +		if (!ric && uc->session)
> > > > +			continue;
> > > >  		if (uc->ret_handler)
> > > > -			uc->ret_handler(uc, ri->func, regs);
> > > > +			uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie : NULL);
> > >
> > > So why do we need the new uc->session member and the uc->session above ?
> > >
> > > If return_consumer_find() returns NULL, uc->ret_handler(..., NULL) can handle
> > > this case itself?
> >
> > I tried to explain that in the comment above.. we do not want to
> > execute session ret_handler at all in this case, because its entry
> > counterpart did not run
> 
> I understand, but the session ret_handler(..., __u64 *data) can simply do
> 
> 	// my ->handler() didn't run or it didn't return 0
> 	if (!data)
> 		return;
> 
> at the start?

I see, that's actualy the only usage of the 'session' flag, so we could
get rid of it and we'd do above check in uprobe_multi layer.. good idea

thanks,
jirka