linux-kernel - Re: [PATCH v7 01/16] perf python: Add more exceptions on error paths

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Message-ID: <CAP-5=fVy1bMvMOWSKom10ivTbP_+baWk1=N7jjr4ye+LbM+bbQ@mail.gmail.com>
Date: Wed, 23 Jul 2025 15:24:04 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	James Clark <james.clark@...aro.org>, Xu Yang <xu.yang_2@....com>, 
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>, Collin Funk <collin.funk1@...il.com>, 
	Howard Chu <howardchu95@...il.com>, Weilin Wang <weilin.wang@...el.com>, 
	Andi Kleen <ak@...ux.intel.com>, "Dr. David Alan Gilbert" <linux@...blig.org>, 
	Thomas Richter <tmricht@...ux.ibm.com>, Tiezhu Yang <yangtiezhu@...ngson.cn>, 
	Gautam Menghani <gautam@...ux.ibm.com>, Thomas Falcon <thomas.falcon@...el.com>, 
	Chun-Tse Shao <ctshao@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v7 01/16] perf python: Add more exceptions on error paths

On Wed, Jul 23, 2025 at 11:21 AM Ian Rogers <irogers@...gle.com> wrote:
>
> On Wed, Jul 23, 2025 at 11:13 AM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Mon, Jul 14, 2025 at 09:43:49AM -0700, Ian Rogers wrote:
> > > Returning NULL will cause the python interpreter to fail but not
> > > report an error. If none wants to be returned then Py_None needs
> > > returning. Set the error for the cases returning NULL so that more
> > > meaningful interpreter behavior is had.
> >
> > It looks like you are adding error messages for the failure cases, not
> > adding new exceptions, right?  IIUC returning NULL in pyrf_event__new()
> > ends up having PyErr_NoMemory().  Then now it has different messages?
>
> This change doesn't alter the exception if there already is one. There
> are lots of cases where NULL is being returned for an error but that
> causes the python interpreter to fail/crash. This patch is just adding
> the exceptions and still returning NULL, previously set exceptions are
> left alone. With the exceptions returned the python interpreter does
> something more useful than fail/crash :-)
>
> > >
> > > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > > ---
> > >  tools/perf/util/python.c | 14 +++++++++++---
> > >  1 file changed, 11 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
> > > index 2f28f71325a8..02544387f39d 100644
> > > --- a/tools/perf/util/python.c
> > > +++ b/tools/perf/util/python.c
> > > @@ -475,13 +475,19 @@ static PyObject *pyrf_event__new(const union perf_event *event)
> > >       if ((event->header.type < PERF_RECORD_MMAP ||
> > >            event->header.type > PERF_RECORD_SAMPLE) &&
> > >           !(event->header.type == PERF_RECORD_SWITCH ||
> > > -           event->header.type == PERF_RECORD_SWITCH_CPU_WIDE))
> > > +           event->header.type == PERF_RECORD_SWITCH_CPU_WIDE)){
> > > +             PyErr_Format(PyExc_TypeError, "Unexpected header type %u",
> > > +                          event->header.type);
> > >               return NULL;
> > > +     }
> > >
> > >       // FIXME this better be dynamic or we need to parse everything
> > >       // before calling perf_mmap__consume(), including tracepoint fields.
> > > -     if (sizeof(pevent->event) < event->header.size)
> > > +     if (sizeof(pevent->event) < event->header.size) {
> > > +             PyErr_Format(PyExc_TypeError, "Unexpected event version: %zd < %u",
> >
> > Maybe "Unexpected event size" instead?
>
> I think size is more accurate to the code, version is more useful to
> the user. I believe there is existing use of the event size being used
> as a quasi version number, so I think this description is consistent.
> If you feel strongly I can change it.

Actually I was thinking of the attribute size, let me fix this.

Thanks,
Ian

> Thanks,
> Ian
>
> > Thanks,
> > Namhyung
> >
> >
> > > +                          sizeof(pevent->event), event->header.size);
> > >               return NULL;
> > > +     }
> > >
> > >       ptype = pyrf_event__type[event->header.type];
> > >       pevent = PyObject_New(struct pyrf_event, ptype);
> > > @@ -1199,8 +1205,10 @@ static PyObject *pyrf_evlist__read_on_cpu(struct pyrf_evlist *pevlist,
> > >               return NULL;
> > >
> > >       md = get_md(evlist, cpu);
> > > -     if (!md)
> > > +     if (!md) {
> > > +             PyErr_Format(PyExc_TypeError, "Unknown CPU '%d'", cpu);
> > >               return NULL;
> > > +     }
> > >
> > >       if (perf_mmap__read_init(&md->core) < 0)
> > >               goto end;
> > > --
> > > 2.50.0.727.gbf7dc18ff4-goog
> > >