[PATCH v2 1/2] kernel/events: Add option to notify through signals on wakeup

[Naveen N. Rao]

Add a new option 'signal_on_wakeup' to request for a signal to be
delivered on ring buffer wakeup controlled through watermark and
{wakeup_events, wakeup_watermark}. HUP is signaled on exit.

Setting signal_on_wakeup disables use of IOC_REFRESH to control signal
delivery, instead relying on IOC_ENABLE/DISABLE.

Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
 include/uapi/linux/perf_event.h |  3 ++-
 kernel/events/core.c            | 22 ++++++++++++++--------
 kernel/events/ring_buffer.c     |  3 +++
 3 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index b1c0b187acfe..e5810b1d74a4 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -345,7 +345,8 @@ struct perf_event_attr {
 				context_switch :  1, /* context switch data */
 				write_backward :  1, /* Write ring buffer from end to beginning */
 				namespaces     :  1, /* include namespaces data */
-				__reserved_1   : 35;
+				signal_on_wakeup : 1, /* send signal on wakeup */
+				__reserved_1   : 34;
 
 	union {
 		__u32		wakeup_events;	  /* wakeup every n events */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 426c2ffba16d..4fe708a4fdee 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2680,9 +2680,11 @@ EXPORT_SYMBOL_GPL(perf_event_addr_filters_sync);
 static int _perf_event_refresh(struct perf_event *event, int refresh)
 {
 	/*
-	 * not supported on inherited events
+	 * not supported on inherited events or if user has requested for
+	 * signals on ring buffer wakeup.
 	 */
-	if (event->attr.inherit || !is_sampling_event(event))
+	if (event->attr.inherit || event->attr.signal_on_wakeup ||
+			!is_sampling_event(event))
 		return -EINVAL;
 
 	atomic_add(refresh, &event->event_limit);
@@ -7341,7 +7343,6 @@ static int __perf_event_overflow(struct perf_event *event,
 				   int throttle, struct perf_sample_data *data,
 				   struct pt_regs *regs)
 {
-	int events = atomic_read(&event->event_limit);
 	int ret = 0;
 
 	/*
@@ -7358,12 +7359,15 @@ static int __perf_event_overflow(struct perf_event *event,
 	 * events
 	 */
 
-	event->pending_kill = POLL_IN;
-	if (events && atomic_dec_and_test(&event->event_limit)) {
-		ret = 1;
-		event->pending_kill = POLL_HUP;
+	if (!event->attr.signal_on_wakeup) {
+		int events = atomic_read(&event->event_limit);
+		event->pending_kill = POLL_IN;
+		if (events && atomic_dec_and_test(&event->event_limit)) {
+			ret = 1;
+			event->pending_kill = POLL_HUP;
 
-		perf_event_disable_inatomic(event);
+			perf_event_disable_inatomic(event);
+		}
 	}
 
 	READ_ONCE(event->overflow_handler)(event, data, regs);
@@ -10427,6 +10431,8 @@ perf_event_exit_event(struct perf_event *child_event,
 		perf_group_detach(child_event);
 	list_del_event(child_event, child_ctx);
 	child_event->state = PERF_EVENT_STATE_EXIT; /* is_event_hup() */
+	if (child_event->attr.signal_on_wakeup)
+		child_event->pending_kill = POLL_HUP;
 	raw_spin_unlock_irq(&child_ctx->lock);
 
 	/*
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index ee97196bb151..e7a558cfcadb 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -21,6 +21,9 @@ static void perf_output_wakeup(struct perf_output_handle *handle)
 {
 	atomic_set(&handle->rb->poll, POLLIN);
 
+	if (handle->event->attr.signal_on_wakeup)
+		handle->event->pending_kill = POLL_IN;
+
 	handle->event->pending_wakeup = 1;
 	irq_work_queue(&handle->event->pending);
 }
-- 
2.13.3