[PATCH] ppc highmem fix

[PATCH] ppc highmem fix

[Paolo Galtieri]

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)

Re: [PATCH] ppc highmem fix

[Paolo Galtieri]

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

Re: [PATCH] ppc highmem fix

[Benjamin Herrenschmidt]

On Mon, 2005-10-10 at 16:38 -0700, Paolo Galtieri wrote:
> 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.

Looks good, should probably still make it to 2.6.14, Andrew, Linus ?

(Paolo, can you send them a clean patch ?)

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>


> > --- 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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