linux-kernel - Re: [tip:perf/urgent] perf: Fix perf_event_exit

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Date:	Mon, 25 Jan 2016 14:08:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	torvalds@...ux-foundation.org, eranian@...gle.com,
	tglx@...utronix.de, hpa@...or.com, acme@...hat.com,
	dsahern@...il.com, namhyung@...nel.org, vincent.weaver@...ne.edu,
	jolsa@...hat.com
Cc:	alexander.shishkin@...ux.intel.com
Subject: Re: [tip:perf/urgent] perf: Fix perf_event_exit_task() race


---

Subject: perf: Fix orphan hole
From: Peter Zijlstra <peterz@...radead.org>
Date: Fri Jan 22 22:13:41 CET 2016

We should set event->owner before we install the event, otherwise
there is a hole where the target task can fork() and we'll not inherit
the event because it thinks the event is orphaned.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/events/core.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8489,6 +8489,8 @@ SYSCALL_DEFINE5(perf_event_open,
 	perf_event__header_size(event);
 	perf_event__id_header_size(event);
 
+	event->owner = current;
+
 	perf_install_in_context(ctx, event, event->cpu);
 	perf_unpin_context(ctx);
 
@@ -8498,8 +8500,6 @@ SYSCALL_DEFINE5(perf_event_open,
 
 	put_online_cpus();
 
-	event->owner = current;
-
 	mutex_lock(&current->perf_event_mutex);
 	list_add_tail(&event->owner_entry, &current->perf_event_list);
 	mutex_unlock(&current->perf_event_mutex);