percpu-refcount: support synchronous switch to atomic mode.

percpu_ref_switch_to_atomic_sync() schedules the switch to atomic mode, then
waits for it to complete.

Also export percpu_ref_switch_to_* so they can be used from modules.

This will be used in md/raid to count the number of pending write
requests to an array.
We occasionally need to check if the count is zero, but most often
we don't care.
We always want updates to the counter to be fast, as in some cases
we count every 4K page.

Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 3a481a49546ef1c85d8f88bf7668f8a2c8e8c0f1..c13dceb87b60adbe36c8ae2c7ba21824f33343dd 100644 (file)
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -99,6 +99,7 @@ int __must_check percpu_ref_init(struct percpu_ref *ref,
 void percpu_ref_exit(struct percpu_ref *ref);
 void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
                                 percpu_ref_func_t *confirm_switch);
+void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref);
 void percpu_ref_switch_to_percpu(struct percpu_ref *ref);
 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
                                 percpu_ref_func_t *confirm_kill);

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 9ac959ef4cae972374540f34895465507e656d7b..fe03c6d527611937e196395f83f7348da86f8f06 100644 (file)
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -260,6 +260,22 @@ void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
 
        spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 }
+EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic);
+
+/**
+ * percpu_ref_switch_to_atomic_sync - switch a percpu_ref to atomic mode
+ * @ref: percpu_ref to switch to atomic mode
+ *
+ * Schedule switching the ref to atomic mode, and wait for the
+ * switch to complete.  Caller must ensure that no other thread
+ * will switch back to percpu mode.
+ */
+void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref)
+{
+       percpu_ref_switch_to_atomic(ref, NULL);
+       wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
+}
+EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic_sync);
 
 /**
  * percpu_ref_switch_to_percpu - switch a percpu_ref to percpu mode
@@ -290,6 +306,7 @@ void percpu_ref_switch_to_percpu(struct percpu_ref *ref)
 
        spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 }
+EXPORT_SYMBOL_GPL(percpu_ref_switch_to_percpu);
 
 /**
  * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation