perf: Disallow mmap() on per-task inherited events

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@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 6ae6218..ff5d430 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2593,6 +2593,14 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
        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;