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SubjectRe: [PATCH] ppc highmem fix
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On Mon, 2005-10-10 at 16:20 -0700, Paolo Galtieri wrote:
> I've noticed that the calculations for seg_size and nr_segs in
> __dma_sync_page_highmem() (arch/ppc/kernel/dma-mapping.c) are wrong.
> The incorrect calculations can result in either an oops or a panic when
> running fsck depending on the size of the partition. The problem with
> the
> seg_size calculation is that it can result in a negative number if size
> is offset > size. The problem with the nr_segs caculation is returns
> the
> wrong number of segments, e.g. it returns 1 when size is 200 and offset
> is 4095, when it should return 2 or more.
>
> Here is the patch to fix the problem.
>
> --- linux-2.6.14-rc3-git8/arch/ppc/kernel/dma-mapping.c 2005-10-10
> 13:55:37.000000000 -0700
> +++ linux-2.6.14/arch/ppc/kernel/dma-mapping.c 2005-10-10
> 13:57:51.000000000 -0700
> @@ -401,10 +401,10 @@
> static inline void __dma_sync_page_highmem(struct page *page,
> unsigned long offset, size_t size, int direction)
> {
> - size_t seg_size = min((size_t)PAGE_SIZE, size) - offset;
> + size_t seg_size = min((size_t)(PAGE_SIZE - offset), size);
> size_t cur_size = seg_size;
> unsigned long flags, start, seg_offset = offset;
> - int nr_segs = PAGE_ALIGN(size + (PAGE_SIZE - offset))/PAGE_SIZE;
> + int nr_segs = 1 + ((size - seg_size) + PAGE_SIZE - 1)/PAGE_SIZE;
> int seg_nr = 0;
>
> local_irq_save(flags);
>
>
> Paolo Galtieri (pgaltieri@mvista.com)
>

I want to apologize in advance for the previous post. When I included
the patch inline I dropped the tabs :-(. Here is the correct patch with
tabs:

--- linux-2.6.14-rc3-git8/arch/ppc/kernel/dma-mapping.c 2005-10-10
13:55:37.000000000 -0700
+++ linux-2.6.14/arch/ppc/kernel/dma-mapping.c 2005-10-10
13:57:51.000000000 -0700
@@ -401,10 +401,10 @@
static inline void __dma_sync_page_highmem(struct page *page,
unsigned long offset, size_t size, int direction)
{
- size_t seg_size = min((size_t)PAGE_SIZE, size) - offset;
+ size_t seg_size = min((size_t)(PAGE_SIZE - offset), size);
size_t cur_size = seg_size;
unsigned long flags, start, seg_offset = offset;
- int nr_segs = PAGE_ALIGN(size + (PAGE_SIZE - offset))/PAGE_SIZE;
+ int nr_segs = 1 + ((size - seg_size) + PAGE_SIZE - 1)/PAGE_SIZE;
int seg_nr = 0;

local_irq_save(flags);
Paolo

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