[PATCH 10/12] perf: make nr_events an int and add perf_online_mutex to protect it

Tejun Heo
2010-05-04T12:39:26Z

Change nr_events from atomic_t to int and add perf_online_mutex to
protect it. Helpers to manipulate the count, perf_inc_nr_events() and
perf_dec_nr_events(), are added. The former may fail although it
doesn't in the current code.

This will be used to make sched perf functions called via tracepoints.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
---
kernel/perf_event.c | 40 ++++++++++++++++++++++++++++++++++++----
1 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3f3e328..621d1f1 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -43,7 +43,7 @@ int perf_max_events __read_mostly = 1;
static int perf_reserved_percpu __read_mostly;
static int perf_overcommit __read_mostly = 1;

-static atomic_t nr_events __read_mostly;
+static int nr_events __read_mostly;
static atomic_t nr_mmap_events __read_mostly;
static atomic_t nr_comm_events __read_mostly;
static atomic_t nr_task_events __read_mostly;
@@ -72,6 +72,26 @@ static atomic64_t perf_event_id;
static DEFINE_SPINLOCK(perf_resource_lock);

/*
+ * Lock to protect nr_events and master enable:
+ */
+static DEFINE_MUTEX(perf_online_mutex);
+
+static int perf_inc_nr_events(void)
+{
+ mutex_lock(&perf_online_mutex);
+ nr_events++;
+ mutex_unlock(&perf_online_mutex);
+ return 0;
+}
+
+static void perf_dec_nr_events(void)
+{
+ mutex_lock(&perf_online_mutex);
+ nr_events--;
+ mutex_unlock(&perf_online_mutex);
+}
+
+/*
* Architecture provided APIs - weak aliases:
*/
extern __weak const struct pmu *hw_perf_event_init(struct perf_event *event)
@@ -1589,7 +1609,13 @@ void perf_event_task_tick(struct task_struct *curr)
struct perf_event_context *ctx;
int rotate = 0;

- if (!atomic_read(&nr_events))
+ /*
+ * nr_events is incremented before events are enabled and
+ * decremented after they have been pulled out, so it is
+ * guaranteed to read as non-zero with any enabled event on
+ * this cpu.
+ */
+ if (!nr_events)
return;

cpuctx = &__get_cpu_var(perf_cpu_context);
@@ -1857,7 +1883,7 @@ static void free_event(struct perf_event *event)
perf_pending_sync(event);

if (!event->parent) {
- atomic_dec(&nr_events);
+ perf_dec_nr_events();
if (event->attr.mmap)
atomic_dec(&nr_mmap_events);
if (event->attr.comm)
@@ -4569,6 +4595,12 @@ perf_event_alloc(struct perf_event_attr *attr,
if (!event)
return ERR_PTR(-ENOMEM);

+ err = perf_inc_nr_events();
+ if (err) {
+ kfree(event);
+ return ERR_PTR(err);
+ }
+
/*
* Single events are their own group leaders, with an
* empty sibling list:
@@ -4657,6 +4689,7 @@ done:
if (err) {
if (event->ns)
put_pid_ns(event->ns);
+ perf_dec_nr_events();
kfree(event);
return ERR_PTR(err);
}
@@ -4664,7 +4697,6 @@ done:
event->pmu = pmu;

if (!event->parent) {
- atomic_inc(&nr_events);
if (event->attr.mmap)
atomic_inc(&nr_mmap_events);
if (event->attr.comm)
--
1.6.4.2