afs: don't use PREPARE_WORK

PREPARE_[DELAYED_]WORK() are being phased out.  They have few users
and a nasty surprise in terms of reentrancy guarantee as workqueue
considers work items to be different if they don't have the same work
function.

afs_call->async_work is multiplexed with multiple work functions.
Introduce afs_async_workfn() which invokes afs_call->async_workfn and
always use it as the work function and update the users to set the
->async_workfn field instead of overriding the work function using
PREPARE_WORK().

It would probably be best to route this with other related updates
through the workqueue tree.

Compile tested.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: linux-afs@lists.infradead.org

fs/afs/internal.h

@@ -75,6 +75,7 @@ struct afs_call {
 	const struct afs_call_type *type;	/* type of call */
 	const struct afs_wait_mode *wait_mode;	/* completion wait mode */
 	wait_queue_head_t	waitq;		/* processes awaiting completion */
+	work_func_t		async_workfn;
 	struct work_struct	async_work;	/* asynchronous work processor */
 	struct work_struct	work;		/* actual work processor */
 	struct sk_buff_head	rx_queue;	/* received packets */

fs/afs/rxrpc.c

@@ -644,7 +644,7 @@ static void afs_process_async_call(struct work_struct *work)
 
 		/* we can't just delete the call because the work item may be
 		 * queued */
-		PREPARE_WORK(&call->async_work, afs_delete_async_call);
+		call->async_workfn = afs_delete_async_call;
 		queue_work(afs_async_calls, &call->async_work);
 	}
 
@@ -663,6 +663,13 @@ void afs_transfer_reply(struct afs_call *call, struct sk_buff *skb)
 	call->reply_size += len;
 }
 
+static void afs_async_workfn(struct work_struct *work)
+{
+	struct afs_call *call = container_of(work, struct afs_call, async_work);
+
+	call->async_workfn(work);
+}
+
 /*
  * accept the backlog of incoming calls
  */
@@ -685,7 +692,8 @@ static void afs_collect_incoming_call(struct work_struct *work)
 				return;
 			}
 
-			INIT_WORK(&call->async_work, afs_process_async_call);
+			call->async_workfn = afs_process_async_call;
+			INIT_WORK(&call->async_work, afs_async_workfn);
 			call->wait_mode = &afs_async_incoming_call;
 			call->type = &afs_RXCMxxxx;
 			init_waitqueue_head(&call->waitq);