Re: [PATCH 0/6] get rid of on-stack dma buffers

Am Dienstag, 22. März 2011, 14:08:17 schrieb Florian Mickler:

Am 22.03.2011 12:10 schrieb "Roedel, Joerg" [off-list ref]:

quoted

On Mon, Mar 21, 2011 at 05:03:15PM -0400, Florian Mickler wrote:

quoted

I guess (not verified), that the dma api takes sufficient precautions
to abort the dma transfer if a timeout happens.  So freeing _should_
not be an issue. (At least, I would expect big fat warnings everywhere
if that were the case)

Freeing is very well an issue. All you can expect from the DMA-API is to
give you a valid DMA handle for your device. But it can not prevent that
a device uses this handle after you returned it. You need to make sure
yourself that any pending DMA is canceled before calling kfree().

Does usb_control_msg do this? It waits for completion but takes also a
timeout parameter. I will recheck this once I'm home.

It uses usb_start_wait_urb() which upon a timeout kills the URB. The
buffer is unused after usb_control_msg() returns.

	HTH
		Oliver