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

Adrian Hunter
2014-07-23T06:08:33Z

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@intel.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
>
>