percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero()

[pandora-kernel.git] / lib / percpu-refcount.c

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index ac42991..fe5a334 100644 (file)
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -60,6 +60,41 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
 }
 EXPORT_SYMBOL_GPL(percpu_ref_init);
 
+/**
+ * percpu_ref_reinit - re-initialize a percpu refcount
+ * @ref: perpcu_ref to re-initialize
+ *
+ * Re-initialize @ref so that it's in the same state as when it finished
+ * percpu_ref_init().  @ref must have been initialized successfully, killed
+ * and reached 0 but not exited.
+ *
+ * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
+ * this function is in progress.
+ */
+void percpu_ref_reinit(struct percpu_ref *ref)
+{
+       unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
+       int cpu;
+
+       BUG_ON(!pcpu_count);
+       WARN_ON(!percpu_ref_is_zero(ref));
+
+       atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS);
+
+       /*
+        * Restore per-cpu operation.  smp_store_release() is paired with
+        * smp_read_barrier_depends() in __pcpu_ref_alive() and guarantees
+        * that the zeroing is visible to all percpu accesses which can see
+        * the following PCPU_REF_DEAD clearing.
+        */
+       for_each_possible_cpu(cpu)
+               *per_cpu_ptr(pcpu_count, cpu) = 0;
+
+       smp_store_release(&ref->pcpu_count_ptr,
+                         ref->pcpu_count_ptr & ~PCPU_REF_DEAD);
+}
+EXPORT_SYMBOL_GPL(percpu_ref_reinit);
+
 /**
  * percpu_ref_exit - undo percpu_ref_init()
  * @ref: percpu_ref to exit