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Commit f39f87e9 authored by Ian Abbott's avatar Ian Abbott Committed by Greg Kroah-Hartman
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staging: comedi: adl_pci9118: don't overallocate DMA buffer 



The last parameter of `__get_free_pages()` is log2 (the 'order') of the
number of pages to be allocated.  This driver seems to think it is the
linear number of pages, so `pci9118_alloc_dma()` first tries to allocate
16 pages, but only uses 4 of them, setting the buffer size to PAGE_SIZE
multiplied by the 'order'.  If the allocation fails, it tries
progressively smaller orders, down to 0.  If the allocation at order 0
succeeds, the buffer size is set to 0, which is likely to cause
problems.

Set the buffer size to `PAGE_SIZE` shifted left by the allocation order.
Since the maximum buffer size previously used was 4, start with an
allocation order of 2 instead of 4.  Rename the `pages` member of
`struct pci9118_dmabuf` (and the local variable in
`pci9118_alloc_dma()`) to `order` to make it clearer what it is.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Reviewed-by: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d5733baf

drivers/staging/comedi/drivers/adl_pci9118.c

+7 −7
Original line number Diff line number Diff line
@@ -208,7 +208,7 @@ struct pci9118_dmabuf { 
	unsigned long hw;	/* hardware (bus) address of buffer */

	unsigned int size;	/* size of dma buffer in bytes */

	unsigned int use_size;	/* which size we may now use for transfer */

	int pages;		/* number of pages in buffer */

	int order;		/* log2 number of pages in buffer */

};



struct pci9118_private {
@@ -1479,20 +1479,20 @@ static void pci9118_alloc_dma(struct comedi_device *dev) 
{

	struct pci9118_private *devpriv = dev->private;

	struct pci9118_dmabuf *dmabuf;

	int pages;

	int order;

	int i;



	for (i = 0; i < 2; i++) {

		dmabuf = &devpriv->dmabuf[i];

		for (pages = 4; pages >= 0; pages--) {

			dmabuf->virt = __get_free_pages(GFP_KERNEL, pages);

		for (order = 2; order >= 0; order--) {

			dmabuf->virt = __get_free_pages(GFP_KERNEL, order);

			if (dmabuf->virt)

				break;

		}

		if (!dmabuf->virt)

			break;

		dmabuf->pages = pages;

		dmabuf->size = PAGE_SIZE * pages;

		dmabuf->order = order;

		dmabuf->size = PAGE_SIZE << order;

		dmabuf->hw = virt_to_bus((void *)dmabuf->virt);



		if (i == 0)
@@ -1514,7 +1514,7 @@ static void pci9118_free_dma(struct comedi_device *dev) 
	for (i = 0; i < 2; i++) {

		dmabuf = &devpriv->dmabuf[i];

		if (dmabuf->virt)

			free_pages(dmabuf->virt, dmabuf->pages);

			free_pages(dmabuf->virt, dmabuf->order);

	}

}