RCU, workqueue: Implement rcu_work

There are cases where RCU callback needs to be bounced to a sleepable
context.  This is currently done by the RCU callback queueing a work
item, which can be cumbersome to write and confusing to read.

This patch introduces rcu_work, a workqueue work variant which gets
executed after a RCU grace period, and converts the open coded
bouncing in fs/aio and kernel/cgroup.

v3: Dropped queue_rcu_work_on().  Documented rcu grace period behavior
    after queue_rcu_work().

v2: Use rcu_barrier() instead of synchronize_rcu() to wait for
    completion of previously queued rcu callback as per Paul.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index bc0cda180c8b..d026f8f818cc 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -13,6 +13,7 @@
 #include <linux/threads.h>
 #include <linux/atomic.h>
 #include <linux/cpumask.h>
+#include <linux/rcupdate.h>
 
 struct workqueue_struct;
 
@@ -120,6 +121,14 @@ struct delayed_work {
 	int cpu;
 };
 
+struct rcu_work {
+	struct work_struct work;
+	struct rcu_head rcu;
+
+	/* target workqueue ->rcu uses to queue ->work */
+	struct workqueue_struct *wq;
+};
+
 /**
  * struct workqueue_attrs - A struct for workqueue attributes.
  *
@@ -151,6 +160,11 @@ static inline struct delayed_work *to_delayed_work(struct work_struct *work)
 	return container_of(work, struct delayed_work, work);
 }
 
+static inline struct rcu_work *to_rcu_work(struct work_struct *work)
+{
+	return container_of(work, struct rcu_work, work);
+}
+
 struct execute_work {
 	struct work_struct work;
 };
@@ -266,6 +280,12 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
 #define INIT_DEFERRABLE_WORK_ONSTACK(_work, _func)			\
 	__INIT_DELAYED_WORK_ONSTACK(_work, _func, TIMER_DEFERRABLE)
 
+#define INIT_RCU_WORK(_work, _func)					\
+	INIT_WORK(&(_work)->work, (_func))
+
+#define INIT_RCU_WORK_ONSTACK(_work, _func)				\
+	INIT_WORK_ONSTACK(&(_work)->work, (_func))
+
 /**
  * work_pending - Find out whether a work item is currently pending
  * @work: The work item in question
@@ -447,6 +467,7 @@ extern bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 			struct delayed_work *work, unsigned long delay);
 extern bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
 			struct delayed_work *dwork, unsigned long delay);
+extern bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork);
 
 extern void flush_workqueue(struct workqueue_struct *wq);
 extern void drain_workqueue(struct workqueue_struct *wq);
@@ -463,6 +484,8 @@ extern bool flush_delayed_work(struct delayed_work *dwork);
 extern bool cancel_delayed_work(struct delayed_work *dwork);
 extern bool cancel_delayed_work_sync(struct delayed_work *dwork);
 
+extern bool flush_rcu_work(struct rcu_work *rwork);
+
 extern void workqueue_set_max_active(struct workqueue_struct *wq,
 				     int max_active);
 extern struct work_struct *current_work(void);