kref: fix CPU ordering with respect to krefs

some atomic operations are only atomic, not ordered. Thus a CPU is allowed
to reorder memory references to an object to before the reference is
obtained. This fixes it.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/kref.c b/lib/kref.c
index 0d07cc31c818..a6dc3ec328e0 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -21,6 +21,7 @@
 void kref_init(struct kref *kref)
 {
         atomic_set(&kref->refcount,1);
+        smp_mb();
 }
 
 /**
@@ -31,6 +32,7 @@ void kref_get(struct kref *kref)
 {
         WARN_ON(!atomic_read(&kref->refcount));
         atomic_inc(&kref->refcount);
+        smp_mb__after_atomic_inc();
 }
 
 /**