[PATCH 3/4] perf tools: Fix probing the kernel API with cpu-wide events

[Adrian Hunter]

Fall back to probing with the current pid if cpu-wide
probing fails.  This primarily affects the setting of
comm_exec flag when the user is un-privileged and
/proc/sys/kernel/perf_event_paranoid > 0.  The change
to comm_exec can be observed by using -vv with
perf record and a kernel that supports comm_exec.

Signed-off-by: Adrian Hunter <adrian.hun...@intel.com>
---
 tools/perf/util/record.c | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index 68ad2d0..cf69325 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -14,6 +14,7 @@ static int perf_do_probe_api(setup_probe_fn_t fn, int cpu, 
const char *str)
        struct perf_evsel *evsel;
        unsigned long flags = perf_event_open_cloexec_flag();
        int err = -EAGAIN, fd;
+       static pid_t pid = -1;
 
        evlist = perf_evlist__new();
        if (!evlist)
@@ -24,14 +25,22 @@ static int perf_do_probe_api(setup_probe_fn_t fn, int cpu, 
const char *str)
 
        evsel = perf_evlist__first(evlist);
 
-       fd = sys_perf_event_open(&evsel->attr, -1, cpu, -1, flags);
-       if (fd < 0)
-               goto out_delete;
+       while (1) {
+               fd = sys_perf_event_open(&evsel->attr, pid, cpu, -1, flags);
+               if (fd < 0) {
+                       if (pid == -1 && errno == EACCES) {
+                               pid = 0;
+                               continue;
+                       }
+                       goto out_delete;
+               }
+               break;
+       }
        close(fd);
 
        fn(evsel);
 
-       fd = sys_perf_event_open(&evsel->attr, -1, cpu, -1, flags);
+       fd = sys_perf_event_open(&evsel->attr, pid, cpu, -1, flags);
        if (fd < 0) {
                if (errno == EINVAL)
                        err = -EINVAL;
@@ -201,6 +210,7 @@ bool perf_evlist__can_select_event(struct perf_evlist 
*evlist, const char *str)
        struct perf_evsel *evsel;
        int err, fd, cpu;
        bool ret = false;
+       pid_t pid = -1;
 
        temp_evlist = perf_evlist__new();
        if (!temp_evlist)
@@ -221,12 +231,20 @@ bool perf_evlist__can_select_event(struct perf_evlist 
*evlist, const char *str)
                cpu = evlist->cpus->map[0];
        }
 
-       fd = sys_perf_event_open(&evsel->attr, -1, cpu, -1,
-                                perf_event_open_cloexec_flag());
-       if (fd >= 0) {
-               close(fd);
-               ret = true;
+       while (1) {
+               fd = sys_perf_event_open(&evsel->attr, pid, cpu, -1,
+                                        perf_event_open_cloexec_flag());
+               if (fd < 0) {
+                       if (pid == -1 && errno == EACCES) {
+                               pid = 0;
+                               continue;
+                       }
+                       goto out_delete;
+               }
+               break;
        }
+       close(fd);
+       ret = true;
 
 out_delete:
        perf_evlist__delete(temp_evlist);
-- 
1.8.3.2

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