linux-kernel - [PATCH] perf tools: Fix PERF_FLAG_FD_CLOEXEC flag probing event type open counters due to EBUSY error

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Date:	Sun, 3 Aug 2014 14:10:36 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Yann Droneaud <ydroneaud@...eya.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	William Cohen <wcohen@...hat.com>
Subject: [PATCH] perf tools: Fix PERF_FLAG_FD_CLOEXEC flag probing event type
 open counters due to EBUSY error

On Sat, Aug 02, 2014 at 07:58:25PM +0200, Yann Droneaud wrote:
> Hi Jiri,

SNIP

> >  	err = errno;
> >  
> > -	if (WARN_ONCE(fd < 0,
> > +	if (WARN_ONCE(fd < 0 && err != EBUSY,
> >  		      "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
> >  		      err, strerror(err)))
> >  		return -1;
> 
> It's definitely possible to shortcut the function if EBUSY is returned
> by first call to perf_event_open().
> 
> diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
> index dc360ebde745..d5c626d5432a 100644
> --- a/tools/perf/util/cloexec.c
> +++ b/tools/perf/util/cloexec.c
> @@ -25,6 +25,9 @@ static int perf_flag_probe(void)
>  		return 1;
>  	}
>  
> +	if (err == EBUSY)
> +		return -1;
> +
>  	WARN_ONCE(err != EINVAL,
>  		  "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
>  		  err, strerror(err));

heh, I haven't realized that your probing event was
PERF_COUNT_SW_CPU_CLOCK, which could never be busy
and found following bug ;-)

jirka


---
We were using PERF_COUNT_SW_CPU_CLOCK as an probing event type.
Using expected PERF_TYPE_SOFTWARE type instead.

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: David Ahern <dsahern@...il.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Namhyung Kim <namhyung@...il.com>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: William Cohen <wcohen@...hat.com>
Cc: Yann Droneaud <ydroneaud@...eya.com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/util/cloexec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
index dc360ebde745..0f7eb0a53d4b 100644
--- a/tools/perf/util/cloexec.c
+++ b/tools/perf/util/cloexec.c
@@ -9,7 +9,7 @@ static int perf_flag_probe(void)
 {
 	/* use 'safest' configuration as used in perf_evsel__fallback() */
 	struct perf_event_attr attr = {
-		.type = PERF_COUNT_SW_CPU_CLOCK,
+		.type = PERF_TYPE_SOFTWARE,
 		.config = PERF_COUNT_SW_CPU_CLOCK,
 	};
 	int fd;
-- 
1.8.3.1

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