Re: [PATCH v6 6/7] perf dso: Reference counting related fixes

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Mon, May 06, 2024 at 08:26:02AM -0700, Ian Rogers wrote:
> On Mon, May 6, 2024 at 7:44 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> > On Sat, May 04, 2024 at 02:38:02PM -0700, Ian Rogers wrote:
> > > Ensure gets and puts are better aligned fixing reference couting
> > > checking problems.
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > >  tools/perf/util/machine.c    |  4 +--
> > >  tools/perf/util/map.c        |  1 +
> > >  tools/perf/util/symbol-elf.c | 51 ++++++++++++++++++------------------
> > >  3 files changed, 28 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > > index 0b8fb14f5ff6..4a4541a2e887 100644
> > > --- a/tools/perf/util/machine.c
> > > +++ b/tools/perf/util/machine.c
> > > @@ -683,7 +683,7 @@ static int machine__process_ksymbol_register(struct machine *machine,
> > >                                            struct perf_sample *sample __maybe_unused)
> > >  {
> > >       struct symbol *sym;
> > > -     struct dso *dso;
> > > +     struct dso *dso = NULL;
> > >       struct map *map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
> > >       int err = 0;
> > >
> > > @@ -696,7 +696,6 @@ static int machine__process_ksymbol_register(struct machine *machine,
> > >               }
> > >               dso__set_kernel(dso, DSO_SPACE__KERNEL);
> > >               map = map__new2(0, dso);
> > > -             dso__put(dso);
> > >               if (!map) {
> > >                       err = -ENOMEM;
> > >                       goto out;
> > > @@ -735,6 +734,7 @@ static int machine__process_ksymbol_register(struct machine *machine,
> > >       dso__insert_symbol(dso, sym);
> > >  out:
> > >       map__put(map);
> > > +     dso__put(dso);
> > >       return err;
> > >  }
> >
> > This seems to match the patch description, good, just aligning the puts
> >
> > > diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> > > index 117c4bb78b35..e1d14936a60d 100644
> > > --- a/tools/perf/util/map.c
> > > +++ b/tools/perf/util/map.c
> > > @@ -200,6 +200,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> > >                               dso__set_build_id(dso, dso__bid(header_bid_dso));
> > >                               dso__set_header_build_id(dso, 1);
> > >                       }
> > > +                     dso__put(header_bid_dso);
> > >               }
> > >               dso__put(dso);
> > >       }
> >
> > But this is a missing one, so not aligning, but fixing a separate issue,
> > i.e. a missing put? Should go on a different patch, probably with a
> > Fixes.
> 
> The Fixes would be for a patch in the series - albeit that we've spent

Well, if it fixes something that got merged before, it should have the
Fixes, please then have it in the patch fixing it:

Fixes: f649ed80f3cabbf1 ("perf dsos: Tidy reference counting and locking")

> over half a year landing this and a month since that change landed:
> https://lore.kernel.org/all/20240410064214.2755936-3-irogers@google.com/
> The issue is that previously a find wouldn't do a get, so per the old
> code no put is necessary. Gets were added to finds to cover the race
> between a dso being returned from dsos and the item potentially being
> removed from dsos.

The last patch applied:

⬢[acme@toolbox perf-tools-next]$ git log --oneline -1
ee756ef7491eafd7 (HEAD -> perf-tools-next, perf-tools-next.korg/tmp.perf-tools-next) perf dso: Add reference count checking and accessor functions
⬢[acme@toolbox perf-tools-next]$

Needed this, which I applied and pushed to tmp.perf-tools-next:

  util/symbol.c: In function ‘dso__load_bfd_symbols’:
  util/symbol.c:1683:9: error: too few arguments to function ‘dso__set_adjust_symbols’
   1683 |         dso__set_adjust_symbols(dso);
        |         ^~~~~~~~~~~~~~~~~~~~~~~
  In file included from util/symbol.c:21:
  util/dso.h:268:20: note: declared here
    268 | static inline void dso__set_adjust_symbols(struct dso *dso, bool val)
        |                    ^~~~~~~~~~~~~~~~~~~~~~~
  make[6]: *** [/home/acme/git/perf-tools-next/tools/build/Makefile.build:106: /tmp/tmp.ZWHbQftdN6/util/symbol.o] Error 1
    MKDIR   /tmp/tmp.ZWHbQftdN6/tests/workloads/
  make[6]: *** Waiting for unfinished jobs....

This was updated:

  -       symbols__fixup_end(&dso->symbols, false);
  -       symbols__fixup_duplicate(&dso->symbols);
  -       dso->adjust_symbols = 1;
  +       symbols__fixup_end(dso__symbols(dso), false);
  +       symbols__fixup_duplicate(dso__symbols(dso));
  +       dso__set_adjust_symbols(dso);

But not build tested with BUILD_NONDISTRO and libbfd devel files installed
(binutils-devel on fedora), I noticed it using 'make -C tools/perf build-test'.

Add the missing argument:

   	symbols__fixup_end(dso__symbols(dso), false);
   	symbols__fixup_duplicate(dso__symbols(dso));
  -	dso__set_adjust_symbols(dso);
  +	dso__set_adjust_symbols(dso, true);