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

Arnaldo Carvalho de Melo
2014-07-22T14:00:40Z

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...

Anyway, I'll take this patch.

- 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