Merge branch 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu
Pull percpu changes from Tejun Heo:
"Nothing too interesting. One cleanup patch and another to add a
trivial state check function"
* 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
percpu_ref: implement percpu_ref_is_dying()
percpu_ref: remove unnecessary ACCESS_ONCE() in percpu_ref_tryget_live()
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index b433764..12c9b48 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -128,8 +128,22 @@
static inline bool __ref_is_percpu(struct percpu_ref *ref,
unsigned long __percpu **percpu_countp)
{
- /* paired with smp_store_release() in percpu_ref_reinit() */
- unsigned long percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
+ unsigned long percpu_ptr;
+
+ /*
+ * The value of @ref->percpu_count_ptr is tested for
+ * !__PERCPU_REF_ATOMIC, which may be set asynchronously, and then
+ * used as a pointer. If the compiler generates a separate fetch
+ * when using it as a pointer, __PERCPU_REF_ATOMIC may be set in
+ * between contaminating the pointer value, meaning that
+ * ACCESS_ONCE() is required when fetching it.
+ *
+ * Also, we need a data dependency barrier to be paired with
+ * smp_store_release() in __percpu_ref_switch_to_percpu().
+ *
+ * Use lockless deref which contains both.
+ */
+ percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
/*
* Theoretically, the following could test just ATOMIC; however,
@@ -233,7 +247,7 @@
if (__ref_is_percpu(ref, &percpu_count)) {
this_cpu_inc(*percpu_count);
ret = true;
- } else if (!(ACCESS_ONCE(ref->percpu_count_ptr) & __PERCPU_REF_DEAD)) {
+ } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) {
ret = atomic_long_inc_not_zero(&ref->count);
}
@@ -281,6 +295,20 @@
}
/**
+ * percpu_ref_is_dying - test whether a percpu refcount is dying or dead
+ * @ref: percpu_ref to test
+ *
+ * Returns %true if @ref is dying or dead.
+ *
+ * This function is safe to call as long as @ref is between init and exit
+ * and the caller is responsible for synchronizing against state changes.
+ */
+static inline bool percpu_ref_is_dying(struct percpu_ref *ref)
+{
+ return ref->percpu_count_ptr & __PERCPU_REF_DEAD;
+}
+
+/**
* percpu_ref_is_zero - test whether a percpu refcount reached zero
* @ref: percpu_ref to test
*