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-rw-r--r--lib/percpu-refcount.c86
1 files changed, 54 insertions, 32 deletions
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 963b7034a51b..fe5a3342e960 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -31,6 +31,11 @@
#define PCPU_COUNT_BIAS (1U << 31)
+static unsigned __percpu *pcpu_count_ptr(struct percpu_ref *ref)
+{
+ return (unsigned __percpu *)(ref->pcpu_count_ptr & ~PCPU_REF_DEAD);
+}
+
/**
* percpu_ref_init - initialize a percpu refcount
* @ref: percpu_ref to initialize
@@ -46,8 +51,8 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
{
atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS);
- ref->pcpu_count = alloc_percpu(unsigned);
- if (!ref->pcpu_count)
+ ref->pcpu_count_ptr = (unsigned long)alloc_percpu(unsigned);
+ if (!ref->pcpu_count_ptr)
return -ENOMEM;
ref->release = release;
@@ -56,53 +61,71 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
EXPORT_SYMBOL_GPL(percpu_ref_init);
/**
- * percpu_ref_cancel_init - cancel percpu_ref_init()
- * @ref: percpu_ref to cancel init for
+ * percpu_ref_reinit - re-initialize a percpu refcount
+ * @ref: perpcu_ref to re-initialize
*
- * Once a percpu_ref is initialized, its destruction is initiated by
- * percpu_ref_kill() and completes asynchronously, which can be painful to
- * do when destroying a half-constructed object in init failure path.
+ * 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.
*
- * This function destroys @ref without invoking @ref->release and the
- * memory area containing it can be freed immediately on return. To
- * prevent accidental misuse, it's required that @ref has finished
- * percpu_ref_init(), whether successful or not, but never used.
- *
- * The weird name and usage restriction are to prevent people from using
- * this function by mistake for normal shutdown instead of
- * percpu_ref_kill().
+ * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
+ * this function is in progress.
*/
-void percpu_ref_cancel_init(struct percpu_ref *ref)
+void percpu_ref_reinit(struct percpu_ref *ref)
{
- unsigned __percpu *pcpu_count = ref->pcpu_count;
+ unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
int cpu;
- WARN_ON_ONCE(atomic_read(&ref->count) != 1 + PCPU_COUNT_BIAS);
+ 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
+ *
+ * This function exits @ref. The caller is responsible for ensuring that
+ * @ref is no longer in active use. The usual places to invoke this
+ * function from are the @ref->release() callback or in init failure path
+ * where percpu_ref_init() succeeded but other parts of the initialization
+ * of the embedding object failed.
+ */
+void percpu_ref_exit(struct percpu_ref *ref)
+{
+ unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
if (pcpu_count) {
- for_each_possible_cpu(cpu)
- WARN_ON_ONCE(*per_cpu_ptr(pcpu_count, cpu));
- free_percpu(ref->pcpu_count);
+ free_percpu(pcpu_count);
+ ref->pcpu_count_ptr = PCPU_REF_DEAD;
}
}
-EXPORT_SYMBOL_GPL(percpu_ref_cancel_init);
+EXPORT_SYMBOL_GPL(percpu_ref_exit);
static void percpu_ref_kill_rcu(struct rcu_head *rcu)
{
struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
- unsigned __percpu *pcpu_count = ref->pcpu_count;
+ unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
unsigned count = 0;
int cpu;
- /* Mask out PCPU_REF_DEAD */
- pcpu_count = (unsigned __percpu *)
- (((unsigned long) pcpu_count) & ~PCPU_STATUS_MASK);
-
for_each_possible_cpu(cpu)
count += *per_cpu_ptr(pcpu_count, cpu);
- free_percpu(pcpu_count);
-
pr_debug("global %i pcpu %i", atomic_read(&ref->count), (int) count);
/*
@@ -152,11 +175,10 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill)
{
- WARN_ONCE(REF_STATUS(ref->pcpu_count) == PCPU_REF_DEAD,
+ WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,
"percpu_ref_kill() called more than once!\n");
- ref->pcpu_count = (unsigned __percpu *)
- (((unsigned long) ref->pcpu_count)|PCPU_REF_DEAD);
+ ref->pcpu_count_ptr |= PCPU_REF_DEAD;
ref->confirm_kill = confirm_kill;
call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);