From: Eric Dumazet <dada1@cosmosbay.com>
Date: Mon, 30 Jan 2006 05:19:35 +0000 (+0100)
Subject: [PATCH] kref: avoid an atomic operation in kref_put()
X-Git-Tag: upstream/snapshot3+hdmi~42288^2~17
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=8b5536bbee53620f8d5f367987e5727ba36d886d;p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git

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

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@cosmosbay.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

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 (*release)(struct kref *kref))
 	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;
 	}