[tip:perf/core] perf: Ensure that IOC_OUTPUT isn't used to create multi-writer buffers

tip-bot for Peter Zijlstra
2010-05-21T11:29:10Z

Commit-ID: 0f139300c9057c16b5833a4636b715b104fe0baa
Gitweb: http://git.kernel.org/tip/0f139300c9057c16b5833a4636b715b104fe0baa
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Thu, 20 May 2010 14:35:15 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 21 May 2010 11:37:57 +0200

perf: Ensure that IOC_OUTPUT isn't used to create multi-writer buffers

Since we want to ensure buffers only have a single
writer, we must avoid creating one with multiple.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20100521090710.528215873@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/perf_event.c | 19 +++++++++++++++++++
1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3f2cc31..7a93252 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4920,6 +4920,13 @@ static int perf_event_set_output(struct perf_event *event, int output_fd)
int fput_needed = 0;
int ret = -EINVAL;

+ /*
+ * Don't allow output of inherited per-task events. This would
+ * create performance issues due to cross cpu access.
+ */
+ if (event->cpu == -1 && event->attr.inherit)
+ return -EINVAL;
+
if (!output_fd)
goto set;

@@ -4940,6 +4947,18 @@ static int perf_event_set_output(struct perf_event *event, int output_fd)
if (event->data)
goto out;

+ /*
+ * Don't allow cross-cpu buffers
+ */
+ if (output_event->cpu != event->cpu)
+ goto out;
+
+ /*
+ * If its not a per-cpu buffer, it must be the same task.
+ */
+ if (output_event->cpu == -1 && output_event->ctx != event->ctx)
+ goto out;
+
atomic_long_inc(&output_file->f_count);