[tip:perf/core] perf: Disallow mmap() on per-task inherited events

From: tip-bot for Peter Zijlstra
Date: Tue May 18 2010 - 13:17:16 EST

Commit-ID: c7920614cebbf269a7c8397ff959a8dcf727465c
Gitweb: http://git.kernel.org/tip/c7920614cebbf269a7c8397ff959a8dcf727465c
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Tue, 18 May 2010 10:33:24 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 18 May 2010 18:35:48 +0200

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@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
kernel/perf_event.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 6ae6218..ff5d430 100644
--- 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;

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