[PATCH 4/5] perf: add 'keep tracking' flag to PERF_EVENT_IOC_DISABLE

[Adrian Hunter <adrian.hunter@intel.com>]

Make it possible to disable an event but continue to receive
"tracking" events i.e. continue to receive mmap, comm, task events.
The flag is updated by both PERF_EVENT_IOC_DISABLE and
PERF_EVENT_IOC_ENABLE.  The flag is cleared by prctl
PR_TASK_PERF_EVENTS_DISABLE.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 include/linux/perf_event.h      |  1 +
 include/uapi/linux/perf_event.h |  1 +
 kernel/events/core.c            | 21 +++++++++++++++++++--
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 50b3efd..789eeeb 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -436,6 +436,7 @@ struct perf_event {
 	struct perf_cgroup		*cgrp; /* cgroup event is attach to */
 	int				cgrp_defer_enabled;
 #endif
+	int				keep_tracking;
 
 #endif /* CONFIG_PERF_EVENTS */
 };
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 663be3f..7b4ecfb 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -324,6 +324,7 @@ struct perf_event_attr {
 
 enum perf_event_ioc_flags {
 	PERF_IOC_FLAG_GROUP		= 1U << 0,
+	PERF_IOC_KEEP_TRACKING		= 1U << 1,
 };
 
 /*
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1db3af9..0c1fbe9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3495,6 +3495,16 @@ static inline int perf_fget_light(int fd, struct fd *p)
 	return 0;
 }
 
+static void perf_event_keep_tracking(struct perf_event *event, u32 flags)
+{
+	int keep_tracking = !!(flags & PERF_IOC_KEEP_TRACKING);
+
+	if (flags & PERF_IOC_FLAG_GROUP)
+		event->group_leader->keep_tracking = keep_tracking;
+	else
+		event->keep_tracking = keep_tracking;
+}
+
 static int perf_event_set_output(struct perf_event *event,
 				 struct perf_event *output_event);
 static int perf_event_set_filter(struct perf_event *event, void __user *arg);
@@ -3510,6 +3520,7 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		func = perf_event_enable;
 		break;
 	case PERF_EVENT_IOC_DISABLE:
+		perf_event_keep_tracking(event, flags);
 		func = perf_event_disable;
 		break;
 	case PERF_EVENT_IOC_RESET:
@@ -3552,6 +3563,9 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	else
 		perf_event_for_each_child(event, func);
 
+	if (cmd == PERF_EVENT_IOC_ENABLE)
+		perf_event_keep_tracking(event, flags);
+
 	return 0;
 }
 
@@ -3572,8 +3586,10 @@ int perf_event_task_disable(void)
 	struct perf_event *event;
 
 	mutex_lock(&current->perf_event_mutex);
-	list_for_each_entry(event, &current->perf_event_list, owner_entry)
+	list_for_each_entry(event, &current->perf_event_list, owner_entry) {
 		perf_event_for_each_child(event, perf_event_disable);
+		event->keep_tracking = 0;
+	}
 	mutex_unlock(&current->perf_event_mutex);
 
 	return 0;
@@ -4670,7 +4686,8 @@ perf_event_aux_ctx(struct perf_event_context *ctx,
 	struct perf_event *event;
 
 	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
-		if (event->state < PERF_EVENT_STATE_INACTIVE)
+		if (event->state < PERF_EVENT_STATE_INACTIVE &&
+		    !event->keep_tracking)
 			continue;
 		if (!event_filter_match(event))
 			continue;
-- 
1.7.11.7