Re: [PATCH dwarves] pahole: avoid adding same struct structure to two rb trees

[Eduard Zingerman <eddyz87@xxxxxxxxx>]

On Mon, 2023-06-05 at 10:47 -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Jun 02, 2023 at 09:08:51PM +0300, Eduard Zingerman escreveu:
> > On Fri, 2023-06-02 at 15:04 -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Fri, Jun 02, 2023 at 04:52:40PM +0300, Eduard Zingerman escreveu:
> > > > Right, you are correct.
> > > > The 'structures__tree = RB_ROOT' part is still necessary, though.
> > > > If you are ok with overall structure of the patch I can resend it w/o bzero().
> 
> > > Humm, so basically this boils down to the following patch?
> 
> > > +++ b/pahole.c
> > > @@ -674,7 +674,12 @@ static void print_ordered_classes(void)
> > >  		__print_ordered_classes(&structures__tree);
> > >  	} else {
> > >  		struct rb_root resorted = RB_ROOT;
> > > -
> > > +#ifdef DEBUG_CHECK_LEAKS
> > > +		// We'll delete structures from structures__tree, since we're
> > > +		// adding them to ther resorted list, better not keep
> > > +		// references there.
> > > +		structures__tree = RB_ROOT;
> > > +#endif
>  
> > But __structures__delete iterates over structures__tree,
> > so it won't delete anything if code like this, right?
>  
> > >  		resort_classes(&resorted, &structures__list);
> > >  		__print_ordered_classes(&resorted);
> > >  	}
> 
> Yeah, I tried to be minimalistic, my version avoids the crash, but
> defeats the DEBUG_CHECK_LEAKS purpose :-\
> 
> How about:
> 
> diff --git a/pahole.c b/pahole.c
> index 6fc4ed6a721b97ab..e843999fde2a8a37 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -673,10 +673,10 @@ static void print_ordered_classes(void)
>  	if (!need_resort) {
>  		__print_ordered_classes(&structures__tree);
>  	} else {
> -		struct rb_root resorted = RB_ROOT;
> +		structures__tree = RB_ROOT;
>  
> -		resort_classes(&resorted, &structures__list);
> -		__print_ordered_classes(&resorted);
> +		resort_classes(&structures__tree, &structures__list);
> +		__print_ordered_classes(&structures__tree);
>  	}
>  }
>  

That would work, but I still think that there is no need to replicate call
to __print_ordered_classes, as long as the same list is passed as an argument,
e.g.:

@@ -670,14 +671,11 @@ static void resort_classes(struct rb_root *resorted, struct list_head *head)
 
 static void print_ordered_classes(void)
 {
-       if (!need_resort) {
-               __print_ordered_classes(&structures__tree);
-       } else {
-               struct rb_root resorted = RB_ROOT;
-
-               resort_classes(&resorted, &structures__list);
-               __print_ordered_classes(&resorted);
+       if (need_resort) {
+               structures__tree = RB_ROOT;
+               resort_classes(&structures__tree, &structures__list);
        }
+       __print_ordered_classes(&structures__tree);
 }