On Mon, 24 Feb 2014, Dan Williams wrote:

> Save someone else the debug cycles of figuring out why a driver's
> transfer request is failing or causing undefined system behavior.
> Buffers submitted for dma must come from GFP allocated / DMA-able
> memory.
> 
> Return -EAGAIN matching the return value for dma_mapping_error() cases.
> 
> Cc: Alan Stern <st...@rowland.harvard.edu>
> Cc: Sarah Sharp <sarah.a.sh...@linux.intel.com>
> Cc: Mathias Nyman <mathias.ny...@linux.intel.com>
> Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
> ---
>  drivers/usb/core/hcd.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 2518c3250750..ff7cd489f55d 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1502,6 +1502,9 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct 
> urb *urb,
>                                       ret = -EAGAIN;
>                               else
>                                       urb->transfer_flags |= URB_DMA_MAP_PAGE;
> +                     } else if (is_vmalloc_addr(urb->transfer_buffer)) {
> +                             WARN_ONCE(1, "transfer buffer not dma 
> capable\n");
> +                             return -EAGAIN;
>                       } else {
>                               urb->transfer_dma = dma_map_single(
>                                               hcd->self.controller,
> 

You mustn't just return -EAGAIN.  Set ret = -EAGAIN and fall through to 
the error-handling pathway.

Alan Stern

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