Commit dc633982 authored Sep 12, 2014 by Jiri Olsa Committed by Ingo Molnar Sep 24, 2014

perf: Do not POLLHUP event if it has children



Currently we return POLLHUP in event polling if the monitored
process is done, but we didn't consider possible children,
that might be still running and producing data.

Before returning POLLHUP making sure that:

   1) the monitored task has exited and that
   2) we don't have any children to monitor

Also adding parent wakeup when the child event is gone.

Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1410520708-19275-1-git-send-email-jolsa@kernel.org


Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4f7cf3a9

kernel/events/core.c

+20 −1

Original line number	Diff line number	Diff line
		@@ -3587,6 +3587,19 @@ static int perf_event_read_one(struct perf_event *event,
		return n * sizeof(u64);
		}

		static bool is_event_hup(struct perf_event *event)
		{
		bool no_children;

		if (event->state != PERF_EVENT_STATE_EXIT)
		return false;

		mutex_lock(&event->child_mutex);
		no_children = list_empty(&event->child_list);
		mutex_unlock(&event->child_mutex);
		return no_children;
		}

		/*
		* Read the performance event - simple non blocking version for now
		*/
		@@ -3632,7 +3645,7 @@ static unsigned int perf_poll(struct file file, poll_table wait)

		poll_wait(file, &event->waitq, wait);

		if (event->state == PERF_EVENT_STATE_EXIT)
		if (is_event_hup(event))
		return events;

		/*
		@@ -7579,6 +7592,12 @@ static void sync_child_event(struct perf_event *child_event,
		list_del_init(&child_event->child_list);
		mutex_unlock(&parent_event->child_mutex);

		/*
		* Make sure user/parent get notified, that we just
		* lost one event.
		*/
		perf_event_wakeup(parent_event);

		/*
		* Release the parent event, if this was the last
		* reference to it.

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