Re: [PATCH v5 16/50] perf maps: Add remove maps function to remove a map based on callback

[Ian Rogers]

On Mon, Dec 4, 2023 at 3:50 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Mon, Nov 27, 2023 at 2:10 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > Removing maps wasn't being done under the write lock. Similar to
> > maps__for_each_map, iterate the entries but in this case remove the
> > entry based on the result of the callback. If an entry was removed
> > then maps_by_name also needs updating, so add missed flush.
> >
> > In dso__load_kcore, the test of map to save would always be false with
> > REFCNT_CHECKING because of a missing RC_CHK_ACCESS.
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
>
> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
>
> A nitpick below,
>
> > ---
> [SNIP]
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index 72f03b875478..30da8a405d11 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -1239,13 +1239,23 @@ static int kcore_mapfn(u64 start, u64 len, u64 pgoff, void *data)
> >         return 0;
> >  }
> >
> > +static bool remove_old_maps(struct map *map, void *data)
> > +{
> > +       const struct map *map_to_save = data;
> > +
> > +       /*
> > +        * We need to preserve eBPF maps even if they are covered by kcore,
> > +        * because we need to access eBPF dso for source data.
> > +        */
> > +       return RC_CHK_ACCESS(map) != RC_CHK_ACCESS(map_to_save) && !__map__is_bpf_prog(map);
>
> RC_CHK_EQUAL(map, map_to_save) ?

Done in v6.

Thanks,
Ian

> Thanks,
> Namhyung
>
>
> > +}
> > +
> >  static int dso__load_kcore(struct dso *dso, struct map *map,
> >                            const char *kallsyms_filename)
> >  {
> >         struct maps *kmaps = map__kmaps(map);
> >         struct kcore_mapfn_data md;
> >         struct map *replacement_map = NULL;
> > -       struct map_rb_node *old_node, *next;
> >         struct machine *machine;
> >         bool is_64_bit;
> >         int err, fd;
> > @@ -1292,17 +1302,7 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> >         }
> >
> >         /* Remove old maps */
> > -       maps__for_each_entry_safe(kmaps, old_node, next) {
> > -               struct map *old_map = old_node->map;
> > -
> > -               /*
> > -                * We need to preserve eBPF maps even if they are
> > -                * covered by kcore, because we need to access
> > -                * eBPF dso for source data.
> > -                */
> > -               if (old_map != map && !__map__is_bpf_prog(old_map))
> > -                       maps__remove(kmaps, old_map);
> > -       }
> > +       maps__remove_maps(kmaps, remove_old_maps, map);
> >         machine->trampolines_mapped = false;
> >
> >         /* Find the kernel map using the '_stext' symbol */
> > --
> > 2.43.0.rc1.413.gea7ed67945-goog
> >