[120/272] kref: add kref_test_and_get

[Greg KH]

2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Jerome Marchand <jmarchan@xxxxxxxxxx>

commit e4a683c899cd5a49f8d684a054c95bd115a0c005 upstream.

Add kref_test_and_get() function, which atomically add a reference only if
refcount is not zero. This prevent to add a reference to an object that is
already being removed.

Signed-off-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 include/linux/kref.h |    1 +
 lib/kref.c           |   12 ++++++++++++
 2 files changed, 13 insertions(+)

--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -23,6 +23,7 @@ struct kref {
 
 void kref_init(struct kref *kref);
 void kref_get(struct kref *kref);
+int kref_test_and_get(struct kref *kref);
 int kref_put(struct kref *kref, void (*release) (struct kref *kref));
 
 #endif /* _KREF_H_ */
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -37,6 +37,18 @@ void kref_get(struct kref *kref)
 }
 
 /**
+ * kref_test_and_get - increment refcount for object only if refcount is not
+ * zero.
+ * @kref: object.
+ *
+ * Return non-zero if the refcount was incremented, 0 otherwise
+ */
+int kref_test_and_get(struct kref *kref)
+{
+	return atomic_inc_not_zero(&kref->refcount);
+}
+
+/**
  * kref_put - decrement refcount for object.
  * @kref: object.
  * @release: pointer to the function that will clean up the object when the


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