Re: [PATCH v2 10/10] perf symbol: Fix ENOENT case for filename__read_build_id

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

On Fri, Dec 05, 2025 at 11:40:12AM -0800, Ian Rogers wrote:
> On Mon, Dec 1, 2025 at 12:55 PM Ian Rogers <irogers@google.com> wrote:
> >
> > Some callers of filename__read_build_id assume the error value must be
> > -1, fix by making them handle all < 0 values.
> >
> > If is_regular_file fails in filename__read_build_id then it could be
> > the file is missing (ENOENT) and it would be wrong to return
> > -EWOULDBLOCK in that case. Fix the logic so -EWOULDBLOCK is only
> > reported if other errors with stat haven't occurred.
> >
> > Fixes: 834ebb5678d7 ("perf tools: Don't read build-ids from non-regular files")
> 
> We might want to prioritize this fix.

Sure.

> 
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/builtin-buildid-cache.c | 6 ++++--
> >  tools/perf/util/symbol.c           | 3 ++-
> >  2 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/perf/builtin-buildid-cache.c b/tools/perf/builtin-buildid-cache.c
> > index c98104481c8a..539e779e3268 100644
> > --- a/tools/perf/builtin-buildid-cache.c
> > +++ b/tools/perf/builtin-buildid-cache.c
> > @@ -276,12 +276,14 @@ static bool dso__missing_buildid_cache(struct dso *dso, int parm __maybe_unused)
> >  {
> >         char filename[PATH_MAX];
> >         struct build_id bid = { .size = 0, };
> > +       int err;
> >
> >         if (!dso__build_id_filename(dso, filename, sizeof(filename), false))
> >                 return true;
> >
> > -       if (filename__read_build_id(filename, &bid) == -1) {
> 
> This check here is clearly wrong when -EWOULDBLOCK is returned from
> James' change.
> 
> > -               if (errno == ENOENT)
> > +       err = filename__read_build_id(filename, &bid);
> > +       if (err < 0) {
> > +               if (err == -ENOENT)
> >                         return false;
> >
> >                 pr_warning("Problems with %s file, consider removing it from the cache\n",
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index 76dc5b70350a..f43e30019e21 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -2008,8 +2008,9 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
> >         if (!filename)
> >                 return -EFAULT;
> >
> > +       errno = 0;
> >         if (!is_regular_file(filename))
> > -               return -EWOULDBLOCK;
> > +               return errno == 0 ? -EWOULDBLOCK : -errno;
> 
> I've made the fix after the other changes as it is simpler to fix in
> one filename__read_build_id rather than all the libbfd, .. variants.
> If we don't want the series in the short-term perhaps we still want to
> carry some parts of this fix.

Yeah, I hesitate to merge a big series at this moment unless it's a
critical and obvious fix.  Can you please separate this change and send
it out?

Thanks,
Namhyung


> 
> >
> >         err = kmod_path__parse(&m, filename);
> >         if (err)
> > --
> > 2.52.0.158.g65b55ccf14-goog
> >