RE: [PATCH] usb: f_fs: avoid race condition with ffs_epfile_io_complete

["Du, Changbin" <changbin.du@intel.com>]

> > To avoid this, just dequeue the request first. After usb_ep_dequeue, the
> > request must be done or canceled.
> >
> > With this change, we can ensure no race condition in f_fs driver. But
> > actually I found some of the udc driver has analogical issue in its
> > dequeue implementation. For example,
> > 1) the dequeue function hold the controller's lock.
> > 2) before driver request controller  to stop transfer, a request
> >    completed.
> > 3) the controller trigger a interrupt, but its irq handler need wait
> >    dequeue function to release the lock.
> > 4) dequeue function give back the request with negative status, and
> >    release lock.
> > 5) irq handler get lock but the request has already been given back.
> >
> 
> get unlock?
> 
> During the interrupt handler, it should only handle the "data complete"
> interrupt on queued request; if the "data complete" interrupt occurs, but
> it belongs to nobody, it will handle noop.
> 
> 
> Best Regards,
> Peter Chen

You are right, but the problem is the request->status is wrong. If the data
send out but report caller as -EINTR, it will introduce duplicate-send
issue.

Regards,
Du, Changbin