linux-kernel - [PATCH 1/2] kref: add kref_test_and

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Date:	Tue, 04 Jan 2011 16:52:26 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Jens Axboe <jaxboe@...ionio.com>,
	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <greg@...ah.com>
Subject: [PATCH 1/2] 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@...hat.com>
---
 include/linux/kref.h |    1 +
 lib/kref.c           |   16 ++++++++++++++++
 2 files changed, 17 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..5f663b9 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -37,6 +37,22 @@ 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)
+{
+	int ret;
+	smp_mb__before_atomic_inc();
+	ret = atomic_inc_not_zero(&kref->refcount);
+	smp_mb__after_atomic_inc();
+	return ret;
+}
+
+/**
  * 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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