linux-kernel - Re: [PATCH RESEND] ARM: DMA: Fix kzalloc flags in __iommu_alloc

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Message-ID: <20150213033243.GC961@arm.com>
Date:	Fri, 13 Feb 2015 03:32:43 +0000
From:	Will Deacon <will.deacon@....com>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@....linux.org.uk>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexandre Courbot <acourbot@...dia.com>
Subject: Re: [PATCH RESEND] ARM: DMA: Fix kzalloc flags in
 __iommu_alloc_buffer()

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 <acourbot@...dia.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Russell King <linux@....linux.org.uk>
> Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  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 <will.deacon@....com>

Will
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