[PATCH 06/23] kref: avoid an atomic operation in kref_put()

[Greg Kroah-Hartman]

Avoid an atomic operation in kref_put() when the last reference is
dropped. On most platforms, atomic_read() is a plan read of the counter
and involves no atomic at all.

Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---

 lib/kref.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

8b5536bbee53620f8d5f367987e5727ba36d886d
diff --git a/lib/kref.c b/lib/kref.c
index 0d07cc3..4a467fa 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -52,7 +52,12 @@ int kref_put(struct kref *kref, void (*r
 	WARN_ON(release == NULL);
 	WARN_ON(release == (void (*)(struct kref *))kfree);
 
-	if (atomic_dec_and_test(&kref->refcount)) {
+	/*
+	 * if current count is one, we are the last user and can release object
+	 * right now, avoiding an atomic operation on 'refcount'
+	 */
+	if ((atomic_read(&kref->refcount) == 1) ||
+	    (atomic_dec_and_test(&kref->refcount))) {
 		release(kref);
 		return 1;
 	}
-- 
1.2.4


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