linux-kernel - Re: [PATCH 4/5] perf tools: Propagate error info from tp

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Message-ID: <CAE_Gge3UTwmoaWNTYhW3z+xADC8ns_i+KA+z+GKU1pgGSbJvqA@mail.gmail.com>
Date:	Mon, 14 Sep 2015 16:59:41 -0400
From:	Raphaël Beamonte <raphael.beamonte@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 4/5] perf tools: Propagate error info from tp_format

2015-09-14 16:53 GMT-04:00 Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>:
> Em Thu, Sep 10, 2015 at 10:24:52AM +0200, Jiri Olsa escreveu:
>> On Wed, Sep 09, 2015 at 05:58:13PM -0300, Arnaldo Carvalho de Melo wrote:
>>
>> SNIP
>>
>> > This kind of stuff is ok, as evsel is a local variable and you kept the
>> > interface for perf_evsel__syscall_newtp(), i.e. it returns NULL if a new
>> > evsel can't be instantiated.
>> >
>> > Ok, but that is a different interface than the one used by
>> > perf_evsel__newtp(), that also instantiates a new evsel.
>> >
>> > So when one thinks about "foo__new()" we now need to check which one of
>> > the two interfaces it uses, if err.h or if the old NULL based failure
>> > reporting one.
>> >
>> > Double tricky if it is foo__new() and foo__new_variant(), as
>> > perf_evsel__syscall_newtp() and perf_evsel__newtp(), i.e. both will
>> > return a "struct perf_evsel" instance, but one using err.h, the other
>> > use NULL.
>> >
>> > Ok, you marked the ones using a comment, wonder if we couldn't use
>> > 'sparse' somehow here, is it used to check IS_ERR() usage in the kernel?
>>
>> hum, not sure.. will check ;-)
>>
>> at least we could mark related functions with __must_check
>> to force the return value check
>>
>> >
>> > Ah, but what about this in trace__event_handler() in builtin-trace.c?
>> >
>> >         if (evsel->tp_format) {
>> >                 event_format__fprintf(evsel->tp_format, sample->cpu,
>> >                                       sample->raw_data, sample->raw_size,
>> >                                       trace->output);
>> >         }
>> >
>> >
>> > Don't we have to use IS_ERR() here? Ok, no, because if setting up
>> > evsel->tp_format fails, then that evsel will be destroyed and
>> > perf_evsel__newtp() will return ERR_PTR(), so it is ok not no use
>> > ERR_PTR(evsel->tp_format) because it will only be != NULL when it was
>> > successfully set up.
>> >
>> > But then, in perf_evsel__newtp_idx if zalloc() fails we will not return
>> > ERR_PTR(), but instead NULL, a-ha, this one seems to be a real bug, no?
>>
>> hate those allocations in declarations.. never do any good ;-)
>>
>> yep, NULL is not an error, so it's real bug, attached patch should fix it
>>
>> thanks,
>> jirka
>
>
> Ok continuing, found two more problems in this patch, fixed as follows,
> merging.
>
> - Arnaldo
>
> diff --git a/tools/perf/tests/mmap-basic.c b/tools/perf/tests/mmap-basic.c
> index 666b67a4df9d..4bb0c5d2059d 100644
> --- a/tools/perf/tests/mmap-basic.c
> +++ b/tools/perf/tests/mmap-basic.c
> @@ -65,7 +65,7 @@ int test__basic_mmap(void)
>
>                 snprintf(name, sizeof(name), "sys_enter_%s", syscall_names[i]);
>                 evsels[i] = perf_evsel__newtp("syscalls", name);
> -               if (evsels[i] == NULL) {
> +               if (IS_ERR(evsels[i]) == NULL) {
>                         pr_debug("perf_evsel__new\n");
>                         goto out_delete_evlist;
>                 }
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 08c20ee4e27d..6b5d1b509148 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -234,7 +234,9 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
>         struct perf_evsel *evsel = zalloc(perf_evsel__object.size);
>         int err = -ENOMEM;
>
> -       if (evsel != NULL) {
> +       if (evsel == NULL) {
> +               goto out_err;
> +       } else {

Is the else really necessary after a goto?

>                 struct perf_event_attr attr = {
>                         .type          = PERF_TYPE_TRACEPOINT,
>                         .sample_type   = (PERF_SAMPLE_RAW | PERF_SAMPLE_TIME |
> @@ -261,6 +263,7 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
>  out_free:
>         zfree(&evsel->name);
>         free(evsel);
> +out_err:
>         return ERR_PTR(err);
>  }
>
> diff --git a/tools/perf/util/trace-event.c b/tools/perf/util/trace-event.c
> index 8e3a60e3e15f..802bb868d446 100644
> --- a/tools/perf/util/trace-event.c
> +++ b/tools/perf/util/trace-event.c
> @@ -100,7 +100,7 @@ struct event_format*
>  trace_event__tp_format(const char *sys, const char *name)
>  {
>         if (!tevent_initialized && trace_event__init2())
> -               return NULL;
> +               return ERR_PTR(-ENOMEM);
>
>         return tp_format(sys, name);
>  }
--
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