Subject: [PATCH RESEND] ARM: DMA: Fix kzalloc flags in __iommu_alloc_buffer()

From: [email-masked] (Will Deacon)
Date: Fri, 13 Feb 2015 03:32:43 +0000

On Wed, Feb 11, 2015 at 09:01:41AM +0000, Alexandre Courbot wrote:
> There doesn't seem to be any valid reason to allocate the pages array
> with the same flags as the buffer itself. Doing so can eventually lead
> to the following safeguard in mm/slab.c to be hit:
> 
> BUG_ON(flags & GFP_SLAB_BUG_MASK);

nit: I can't actually spot this BUG_ON in the kernel.

> This happens when buffers are allocated with __GFP_DMA32 or
> __GFP_HIGHMEM.
> 
> Fix this by allocating the pages array with GFP_KERNEL to follow what is
> done elsewhere in this file. Using GFP_KERNEL in __iommu_alloc_buffer()
> is safe because atomic allocations are handled by __iommu_alloc_atomic().
> 
> Signed-off-by: Alexandre Courbot <[email-masked]>
> Cc: Arnd Bergmann <[email-masked]>
> Cc: Marek Szyprowski <[email-masked]>
> Cc: Russell King <[email-masked]>
> Acked-by: Marek Szyprowski <[email-masked]>
> ---
>  arch/arm/mm/dma-mapping.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 903dba0..170a116 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1106,7 +1106,7 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
>  	int i = 0;
>  
>  	if (array_size <= PAGE_SIZE)
> -		pages = kzalloc(array_size, gfp);
> +		pages = kzalloc(array_size, GFP_KERNEL);
>  	else
>  		pages = vzalloc(array_size);
>  	if (!pages)
> -- 
> 2.3.0

Looks sensible to me:

  Acked-by: Will Deacon <[email-masked]>

Will