greybus: operation: make cancellation synchronous

Make sure to wait for the operation to become inactive before returning
after having cancelled an operation.

This makes sure that any ongoing operation completion callbacks have
finished.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/connection.c

@@ -227,7 +227,6 @@ void gb_connection_destroy(struct gb_connection *connection)
 	if (WARN_ON(!connection))
 		return;
 
-	/* XXX Need to wait for any outstanding requests to complete */
 	if (WARN_ON(!list_empty(&connection->operations))) {
 		list_for_each_entry_safe(operation, next,
 					 &connection->operations, links)

drivers/staging/greybus/operation.c

@@ -10,6 +10,8 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
 #include <linux/workqueue.h>
 
 #include "greybus.h"
@@ -23,6 +25,9 @@ static struct kmem_cache *gb_message_cache;
 /* Workqueue to handle Greybus operation completions. */
 static struct workqueue_struct *gb_operation_workqueue;
 
+/* Wait queue for synchronous cancellations. */
+static DECLARE_WAIT_QUEUE_HEAD(gb_operation_cancellation_queue);
+
 /*
  * Protects access to connection operations lists, as well as
  * updates to operation->errno.
@@ -41,7 +46,15 @@ static inline void gb_operation_get_active(struct gb_operation *operation)
 /* Caller holds operation reference. */
 static inline void gb_operation_put_active(struct gb_operation *operation)
 {
-	atomic_dec(&operation->active);
+	if (atomic_dec_and_test(&operation->active)) {
+		if (atomic_read(&operation->waiters))
+			wake_up(&gb_operation_cancellation_queue);
+	}
+}
+
+static inline bool gb_operation_is_active(struct gb_operation *operation)
+{
+	return atomic_read(&operation->active);
 }
 
 /*
@@ -463,6 +476,7 @@ gb_operation_create_common(struct gb_connection *connection, u8 type,
 	init_completion(&operation->completion);
 	kref_init(&operation->kref);
 	atomic_set(&operation->active, 0);
+	atomic_set(&operation->waiters, 0);
 
 	spin_lock_irqsave(&gb_operations_lock, flags);
 	list_add_tail(&operation->links, &connection->operations);
@@ -873,7 +887,8 @@ void gb_connection_recv(struct gb_connection *connection,
 }
 
 /*
- * Cancel an operation, and record the given error to indicate why.
+ * Cancel an operation synchronously, and record the given error to indicate
+ * why.
  */
 void gb_operation_cancel(struct gb_operation *operation, int errno)
 {
@@ -890,6 +905,11 @@ void gb_operation_cancel(struct gb_operation *operation, int errno)
 			gb_operation_put(operation);
 		}
 	}
+
+	atomic_inc(&operation->waiters);
+	wait_event(gb_operation_cancellation_queue,
+			!gb_operation_is_active(operation));
+	atomic_dec(&operation->waiters);
 }
 EXPORT_SYMBOL_GPL(gb_operation_cancel);
 

drivers/staging/greybus/operation.h

@@ -128,6 +128,7 @@ struct gb_operation {
 
 	struct kref		kref;
 	atomic_t		active;
+	atomic_t		waiters;
 
 	struct list_head	links;		/* connection->operations */
 };