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Subject[PATCH 1/2 v2] kref: add kref_test_and_get

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@redhat.com>
---
include/linux/kref.h | 1 +
lib/kref.c | 12 ++++++++++++
2 files changed, 13 insertions(+)
diff --git a/include/linux/kref.h b/include/linux/kref.h
index 6cc38fc..90b9e44 100644
--- 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_ */
diff --git a/lib/kref.c b/lib/kref.c
index d3d227a..e7a6e10 100644
--- 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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