[PATCH 1/4] atomic-ref: add basic infrastructure for atomic refs based on atomic_t

[Jens Axboe]

Make the atomic_t reference counting from commit f958d7b528b1 generic
and available for other users.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 include/linux/atomic-ref.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 include/linux/atomic-ref.h

diff --git a/include/linux/atomic-ref.h b/include/linux/atomic-ref.h
new file mode 100644
index 000000000000..dfba69dd9d37
--- /dev/null
+++ b/include/linux/atomic-ref.h
@@ -0,0 +1,33 @@
+#ifndef LINUX_ATOMIC_REF_H
+#define LINUX_ATOMIC_REF_H
+
+/*
+ * Shamelessly stolen from the mm implementation of page reference checking,
+ * see commit f958d7b528b1 for details.
+ */
+#define atomic_ref_zero_or_close_to_overflow(ref)	\
+	((unsigned int) atomic_read(ref) + 127u <= 127u)
+
+static inline bool atomic_ref_inc_not_zero(atomic_t *ref)
+{
+	return atomic_inc_not_zero(ref);
+}
+
+static inline bool atomic_ref_put_and_test(atomic_t *ref)
+{
+	WARN_ON_ONCE(atomic_ref_zero_or_close_to_overflow(ref));
+	return atomic_dec_and_test(ref);
+}
+
+static inline void atomic_ref_put(atomic_t *ref)
+{
+	WARN_ON_ONCE(atomic_ref_put_and_test(ref));
+}
+
+static inline void atomic_ref_get(atomic_t *ref)
+{
+	WARN_ON_ONCE(atomic_ref_zero_or_close_to_overflow(ref));
+	atomic_inc(ref);
+}
+
+#endif
-- 
2.34.1


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