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

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Message-ID: <20150910082452.GC19014@krava.brq.redhat.com>
Date:	Thu, 10 Sep 2015 10:24:52 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	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>,
	Raphaël Beamonte <raphael.beamonte@...il.com>
Subject: Re: [PATCH 4/5] perf tools: Propagate error info from tp_format

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


---
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 08c20ee4e27d..162973bec713 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -256,7 +256,7 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
 		perf_evsel__init(evsel, &attr, idx);
 	}
 
-	return evsel;
+	return evsel ?: ERR_PTR(err);
 
 out_free:
 	zfree(&evsel->name);
--
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