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

[John Keeping]

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 <j...@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

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