[PATCH 1/5] perf: Disallow mmap() on per-task inherited events

[Peter Zijlstra]

Since we now have working per-task-per-cpu events for a while,
disallow mmap() on per-task inherited events. Those things were
a performance problem anyway, and doing away with it allows
us to optimize the buffer somewhat by assuming there is only a single
writer.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
 kernel/perf_event.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-2.6/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/kernel/perf_event.c
+++ linux-2.6/kernel/perf_event.c
@@ -2580,6 +2580,14 @@ static int perf_mmap(struct file *file, 
 	long user_extra, extra;
 	int ret = 0;
 
+	/*
+	 * Don't allow mmap() of inherited per-task counters. This would
+	 * create a performance issue due to all children writing to the
+	 * same buffer.
+	 */
+	if (event->cpu == -1 && event->attr.inherit)
+		return -EINVAL;
+
 	if (!(vma->vm_flags & VM_SHARED))
 		return -EINVAL;
 


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