Re: [PATCH] oprofile: check whether oprofile perf enabled in op_overflow_handler()

Robert Richter
2014-01-15T10:24:53Z

On 15.01.14 10:02:44, Weng Meiling wrote:
> On 2014/1/14 23:05, Robert Richter wrote:
> > @@ -94,6 +98,11 @@ static int op_create_counter(int cpu, int event)
> >
> > per_cpu(perf_events, cpu)[event] = pevent;
> >
> > + /* sync perf_events with overflow handler: */
> > + smp_wmb();
> > +
> > + perf_event_enable(pevent);
> > +
>
> Should this step go before the if check:pevent->state != PERF_EVENT_STATE_ACTIVE ?
> Because the attr->disabled is true, So after the perf_event_create_kernel_counter
> the pevent->state is not PERF_EVENT_STATE_ACTIVE.

Right, the check is a problem. We need to move it after the event was
enabled. On error, we need to NULL the event, see below.

-Robert

---
drivers/oprofile/oprofile_perf.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/oprofile/oprofile_perf.c b/drivers/oprofile/oprofile_perf.c
index d5b2732..9dfb236 100644
--- a/drivers/oprofile/oprofile_perf.c
+++ b/drivers/oprofile/oprofile_perf.c
@@ -38,6 +38,9 @@ static void op_overflow_handler(struct perf_event *event,
int id;
u32 cpu = smp_processor_id();

+ /* sync perf_events with op_create_counter(): */
+ smp_rmb();
+
for (id = 0; id < num_counters; ++id)
if (per_cpu(perf_events, cpu)[id] == event)
break;
@@ -68,6 +71,7 @@ static void op_perf_setup(void)
attr->config = counter_config[i].event;
attr->sample_period = counter_config[i].count;
attr->pinned = 1;
+ attr->disabled = 1;
}
}

@@ -85,16 +89,23 @@ static int op_create_counter(int cpu, int event)
if (IS_ERR(pevent))
return PTR_ERR(pevent);

- if (pevent->state != PERF_EVENT_STATE_ACTIVE) {
- perf_event_release_kernel(pevent);
- pr_warning("oprofile: failed to enable event %d "
- "on CPU %d\n", event, cpu);
- return -EBUSY;
- }
-
per_cpu(perf_events, cpu)[event] = pevent;

- return 0;
+ /* sync perf_events with overflow handler: */
+ smp_wmb();
+
+ perf_event_enable(pevent);
+
+ if (pevent->state == PERF_EVENT_STATE_ACTIVE)
+ return 0;
+
+ perf_event_release_kernel(pevent);
+ per_cpu(perf_events, cpu)[event] = NULL;
+
+ pr_warning("oprofile: failed to enable event %d on CPU %d\n",
+ event, cpu);
+
+ return -EBUSY;
}

static void op_destroy_counter(int cpu, int event)
--
1.8.4.2