On 19/02/15 02:01, David Ahern wrote:
> Commit f6edb53c4993ffe92ce521fb449d1c146cea6ec2 converted the probe to
> a CPU wide event first (pid == -1). For kernels that do not support
> the PERF_FLAG_FD_CLOEXEC flag the probe fails with EINVAL. Since this
> errno is not handled pid is not reset to 0 and the subsequent use of
> pid = -1 as an argument brings in an additional failure path if
> perf_event_paranoid > 0:
>
> $ perf record -- sleep 1
> perf_event_open(..., 0) failed unexpectedly with error 13 (Permission denied)
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.007 MB /tmp/perf.data (11 samples) ]
>
> Since this function only needs to get past this check in kernel/events/core.c:
>
> /* for future expandability... */
> if (flags & ~PERF_FLAG_ALL)
> return -EINVAL;
>
> pid = 0 is sufficient to confirm if the flag is supported or not.
>
> Also, ensure the fd of the confirmation check is closed.
>
> Needs to go to 3.18 stable tree as well.
>
> Signed-off-by: David Ahern <[email protected]>
> Cc: Adrian Hunter <[email protected]>
> ---
> tools/perf/util/cloexec.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
> index 47b78b3f0325..3cc34edf2403 100644
> --- a/tools/perf/util/cloexec.c
> +++ b/tools/perf/util/cloexec.c
> @@ -47,16 +47,17 @@ static int perf_flag_probe(void)
> err, strerror_r(err, sbuf, sizeof(sbuf)));
>
> /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
> - fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
> + fd = sys_perf_event_open(&attr, 0, cpu, -1, 0);
I would prefer to avoid pid = 0 unless necessary and so just do the same
thing again i.e.
while (1) {
fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
if (fd < 0 && pid == -1 && errno == EACCES) {
pid = 0;
continue;
}
break;
}
> err = errno;
>
> + if (fd >= 0)
> + close(fd);
> +
> if (WARN_ONCE(fd < 0 && err != EBUSY,
> "perf_event_open(..., 0) failed unexpectedly with error
> %d (%s)\n",
> err, strerror_r(err, sbuf, sizeof(sbuf))))
> return -1;
>
> - close(fd);
> -
> return 0;
> }
>
>
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