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>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3f2cc31..7a93252 100644 (file)
--- 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);
 
 set: