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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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