This is a note to let you know that I've just added the patch titled
kref: Implement kref_get_unless_zero v3
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kref-implement-kref_get_unless_zero-v3.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4b20db3de8dab005b07c74161cb041db8c5ff3a7 Mon Sep 17 00:00:00 2001
From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Date: Tue, 6 Nov 2012 11:31:49 +0000
Subject: kref: Implement kref_get_unless_zero v3
From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
commit 4b20db3de8dab005b07c74161cb041db8c5ff3a7 upstream.
This function is intended to simplify locking around refcounting for
objects that can be looked up from a lookup structure, and which are
removed from that lookup structure in the object destructor.
Operations on such objects require at least a read lock around
lookup + kref_get, and a write lock around kref_put + remove from lookup
structure. Furthermore, RCU implementations become extremely tricky.
With a lookup followed by a kref_get_unless_zero *with return value check*
locking in the kref_put path can be deferred to the actual removal from
the lookup structure and RCU lookups become trivial.
v2: Formatting fixes.
v3: Invert the return value.
Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/kref.h | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -93,4 +93,25 @@ static inline int kref_put(struct kref *
{
return kref_sub(kref, 1, release);
}
+
+/**
+ * kref_get_unless_zero - Increment refcount for object unless it is zero.
+ * @kref: object.
+ *
+ * Return non-zero if the increment succeeded. Otherwise return 0.
+ *
+ * This function is intended to simplify locking around refcounting for
+ * objects that can be looked up from a lookup structure, and which are
+ * removed from that lookup structure in the object destructor.
+ * Operations on such objects require at least a read lock around
+ * lookup + kref_get, and a write lock around kref_put + remove from lookup
+ * structure. Furthermore, RCU implementations become extremely tricky.
+ * With a lookup followed by a kref_get_unless_zero *with return value check*
+ * locking in the kref_put path can be deferred to the actual removal from
+ * the lookup structure and RCU lookups become trivial.
+ */
+static inline int __must_check kref_get_unless_zero(struct kref *kref)
+{
+ return atomic_add_unless(&kref->refcount, 1, 0);
+}
#endif /* _KREF_H_ */
Patches currently in stable-queue which might be from thellstrom@xxxxxxxxxx are
queue-3.4/kref-implement-kref_get_unless_zero-v3.patch
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