[PATCH] ppc highmem fix

From: Paolo Galtieri
Date: Mon Oct 10 2005 - 18:20:44 EST

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
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
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;


Paolo Galtieri (pgaltieri@xxxxxxxxxx)

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