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

[Alexandre Courbot]

On 02/13/2015 12:32 PM, Will Deacon wrote:
> 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.

I have been trying to push this patch for so long that the line in 
question changed in the meantime. :) It is now

        if (unlikely(flags & GFP_SLAB_BUG_MASK)) {
                pr_emerg("gfp: %u\n", flags & GFP_SLAB_BUG_MASK);
                BUG();
        }

in cache_grow, line 2593 of mm/slab.c.

> > 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@xxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> > Acked-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > ---
> >   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@xxxxxxx>

Thanks! I will amend the commit message and resend.
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