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

[Robert Richter <rric@kernel.org>]

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