1 files changed, 48 insertions, 0 deletions
diff --git a/include/linux/hazptr.h b/include/linux/hazptr.h
new file mode 100644
index 00000000000000..935eee97c95e6a
--- /dev/null
+++ b/include/linux/hazptr.h
@@ -0,0 +1,48 @@
+#include <linux/list.h>
+
+typedef void* hazptr_t;
+
+#define HAZPTR_UNUSED (1ul)
+
+struct hazptr_context;
+
+struct hazptr_head {
+	struct rcu_head head;
+};
+
+void init_hazptr_context(struct hazptr_context *hzcp);
+hazptr_t *hazptr_alloc(struct hazptr_context *hzcp);
+void hazptr_free(struct hazptr_context *hzcp, hazptr_t *hzp);
+
+#define hazptr_tryprotect(hzp, p, field)	__hazptr_tryprotect(hzp, p, offset_of(__typeof__(*p), field)
+
+static inline bool __hazptr_tryprotect(hazptr_t *hzp, void **p, unsigned long head_offset)
+{
+	void *ptr;
+	struct hazptr_head *head;
+
+	ptr = READ_ONCE(*p);
+
+	if (ptr == NULL)
+		return false;
+	
+	head = (struct hazptr_head *)ptr + head_offset;
+	
+	WRITE_ONCE(*hzp, head);
+	smp_mb();
+
+	ptr = READ_ONCE(*p); // read again
+	
+	if (ptr + head_offset != *hzp) { // pointer changed
+		WRITE_ONCE(*hzp, NULL);  // reset hazard pointer
+		return false;
+	} else
+		return true;
+}
+
+static inline void hazptr_clear(hazptr_t *hzp)
+{
+	WRITE_ONCE(*hzp, NULL);
+}
+
+void call_hazptr(struct hazptr_head *head, rcu_callback_t func);