[PATCH 5/5] perf/dummy_pmu: Track and disable active events

[Lucas De Marchi]

When unregistering the PMU, disable the currently active events. This
allows userspace to see the change and possibly reacting on it, like
reopening the fd. With perf-stat, "<not counted>" starts to be printed:

        $ stat -e dummy_pmu_0/test-event-1/ -I1000
        1.001227905                 12      dummy_pmu_0/test-event-1/
        2.004009349                 11      dummy_pmu_0/test-event-1/
        3.005785067                  0      dummy_pmu_0/test-event-1/
        4.008565935      <not counted>      dummy_pmu_0/test-event-1/
        5.010446891      <not counted>      dummy_pmu_0/test-event-1/

Signed-off-by: Lucas De Marchi <lucas.demar...@intel.com>
---
 kernel/events/dummy_pmu.c | 40 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/kernel/events/dummy_pmu.c b/kernel/events/dummy_pmu.c
index c07e111bff01..496cb8469a05 100644
--- a/kernel/events/dummy_pmu.c
+++ b/kernel/events/dummy_pmu.c
@@ -14,6 +14,7 @@
 #include <linux/random.h>
 #include <linux/seq_file.h>
 #include <linux/types.h>
+#include <linux/xarray.h>
 
 struct dummy_mod {
        struct dentry *debugfs_root;
@@ -25,6 +26,7 @@ struct dummy_mod {
 struct dummy_pmu {
        struct pmu base;
        char *name;
+       struct xarray active_events;
        bool registered;
 };
 
@@ -97,9 +99,25 @@ static const struct attribute_group *attr_groups[] = {
        NULL,
 };
 
+static void dummy_pmu_event_destroy(struct perf_event *event)
+{
+       struct dummy_pmu *pmu = event_to_pmu(event);
+       unsigned long idx;
+       struct perf_event *e;
+
+       /* Event not active anymore */
+       xa_for_each(&pmu->active_events, idx, e)
+               if (e == event) {
+                       xa_erase(&pmu->active_events, idx);
+                       break;
+               }
+}
+
 static int dummy_pmu_event_init(struct perf_event *event)
 {
        struct dummy_pmu *pmu = event_to_pmu(event);
+       u32 event_id;
+       int ret;
 
        if (!pmu->registered)
                return -ENODEV;
@@ -117,6 +135,13 @@ static int dummy_pmu_event_init(struct perf_event *event)
        if (event->cpu < 0)
                return -EINVAL;
 
+       ret = xa_alloc(&pmu->active_events, &event_id, event,
+                       xa_limit_32b, GFP_KERNEL);
+       if (ret)
+               return ret;
+
+       event->destroy = dummy_pmu_event_destroy;
+
        return 0;
 }
 
@@ -232,6 +257,8 @@ static int device_init(struct dummy_device *d)
        if (ret)
                goto fail;
 
+       xa_init_flags(&d->pmu.active_events, XA_FLAGS_ALLOC);
+
        d->pmu.registered = true;
        pr_info("Device registered: %s\n", d->pmu.name);
 
@@ -248,9 +275,22 @@ static int device_init(struct dummy_device *d)
        return ret;
 }
 
+static void disable_active_events(struct dummy_pmu *pmu)
+{
+       struct perf_event *event;
+       unsigned long idx;
+
+       xa_for_each(&pmu->active_events, idx, event) {
+               xa_erase(&pmu->active_events, idx);
+               perf_event_disable(event);
+       }
+}
+
 static void device_exit(struct dummy_device *d)
 {
        d->pmu.registered = false;
+
+       disable_active_events(&d->pmu);
        perf_pmu_unregister(&d->pmu.base);
 
        pr_info("Device released: %s\n", d->pmu.name);
-- 
2.46.2