[PATCH] usb: gadget: ffs: handle I/O completion in-order

[John Keeping <john@metanate.com>]

By submitting completed transfers to the system workqueue there is no
guarantee that completion events will be queued up in the correct order,
so if a large bulk transfer is being read with aio the data may arrive
in the wrong order.

Create a single-threaded workqueue for FunctionFS so that completed
requests are passed to userspace in the order in which they complete.

Signed-off-by: John Keeping <john@metanate.com>
---
 drivers/usb/gadget/function/f_fs.c | 10 +++++++++-
 drivers/usb/gadget/function/u_fs.h |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index d21874b35cf6..d59d0e890d04 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -780,11 +780,12 @@ static void ffs_epfile_async_io_complete(struct usb_ep *_ep,
 					 struct usb_request *req)
 {
 	struct ffs_io_data *io_data = req->context;
+	struct ffs_data *ffs = io_data->ffs;
 
 	ENTER();
 
 	INIT_WORK(&io_data->work, ffs_user_copy_worker);
-	schedule_work(&io_data->work);
+	queue_work(ffs->io_completion_wq, &io_data->work);
 }
 
 static void __ffs_epfile_read_buffer_free(struct ffs_epfile *epfile)
@@ -1611,6 +1612,7 @@ static void ffs_data_put(struct ffs_data *ffs)
 		BUG_ON(waitqueue_active(&ffs->ev.waitq) ||
 		       waitqueue_active(&ffs->ep0req_completion.wait) ||
 		       waitqueue_active(&ffs->wait));
+		destroy_workqueue(ffs->io_completion_wq);
 		kfree(ffs->dev_name);
 		kfree(ffs);
 	}
@@ -1651,6 +1653,12 @@ static struct ffs_data *ffs_data_new(void)
 
 	ENTER();
 
+	ffs->io_completion_wq = create_singlethread_workqueue("ffs-completion");
+	if (!ffs->io_completion_wq) {
+		kfree(ffs);
+		return NULL;
+	}
+
 	refcount_set(&ffs->ref, 1);
 	atomic_set(&ffs->opened, 0);
 	ffs->state = FFS_READ_DESCRIPTORS;
diff --git a/drivers/usb/gadget/function/u_fs.h b/drivers/usb/gadget/function/u_fs.h
index 540f1c48c1a8..79f70ebf85dc 100644
--- a/drivers/usb/gadget/function/u_fs.h
+++ b/drivers/usb/gadget/function/u_fs.h
@@ -279,6 +279,7 @@ struct ffs_data {
 	}				file_perms;
 
 	struct eventfd_ctx *ffs_eventfd;
+	struct workqueue_struct *io_completion_wq;
 	bool no_disconnect;
 	struct work_struct reset_work;
 
-- 
2.12.2.648.g6730d8bc62.dirty