perf: Update the mmap control page on mmap()

Apparently we didn't update the mmap control page right after mmap(),
which leads to surprises when userspace wants to use it.

Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Arun Sharma <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

kernel/events/core.c

@@ -3534,6 +3534,8 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	event->mmap_user = get_current_user();
 	vma->vm_mm->pinned_vm += event->mmap_locked;
 
+	perf_event_update_userpage(event);
+
 unlock:
 	if (!ret)
 		atomic_inc(&event->mmap_count);