linux-kernel - Re: [PATCH 01/52] perf tools: Fix jump label always changing during tracing

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Message-ID: <53CF5106.8080100@intel.com>
Date:	Wed, 23 Jul 2014 09:07:02 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 01/52] perf tools: Fix jump label always changing during
 tracing

On 07/22/2014 05:00 PM, Arnaldo Carvalho de Melo wrote:
> Em Tue, Jul 22, 2014 at 04:17:10PM +0300, Adrian Hunter escreveu:
>> Intel PT decoding walks the object code to reconstruct
>> the trace.  A jump label change during tracing causes
>> decoding errors.
>>
>> The "Enable close-on-exec flag on perf file descriptor"
>> patch caused there to be always a jump label change.
>>
>> It was found that using a per-cpu context instead of a
>> per-thread context for the probe of the close-on-exec
>> feature, made the problem go away.
> 
> And it is ok for our purposes, as this code just needs to figure out if
> PERF_FLAG_FD_CLOEXEC is present, but I wonder when this kind of thing
> will hit again...

Possibly

> 
> Anyway, I'll take this patch.

Thanks!

> 
> - Arnaldo
>  
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>>  tools/perf/util/cloexec.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
>> index c5d05ec..6a37be5 100644
>> --- a/tools/perf/util/cloexec.c
>> +++ b/tools/perf/util/cloexec.c
>> @@ -1,3 +1,4 @@
>> +#include <sched.h>
>>  #include "util.h"
>>  #include "../perf.h"
>>  #include "cloexec.h"
>> @@ -14,9 +15,13 @@ static int perf_flag_probe(void)
>>  	};
>>  	int fd;
>>  	int err;
>> +	int cpu = sched_getcpu();
>> +
>> +	if (cpu < 0)
>> +		cpu = 0;
>>  
>>  	/* check cloexec flag */
>> -	fd = sys_perf_event_open(&attr, 0, -1, -1,
>> +	fd = sys_perf_event_open(&attr, -1, cpu, -1,
>>  				 PERF_FLAG_FD_CLOEXEC);
>>  	err = errno;
>>  
>> @@ -30,7 +35,7 @@ static int perf_flag_probe(void)
>>  		  err, strerror(err));
>>  
>>  	/* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
>> -	fd = sys_perf_event_open(&attr, 0, -1, -1, 0);
>> +	fd = sys_perf_event_open(&attr, -1, cpu, -1, 0);
>>  	err = errno;
>>  
>>  	if (WARN_ONCE(fd < 0,
>> -- 
>> 1.8.3.2
> 
> 

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