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

From: Alexandre Courbot
Date: Fri Feb 13 2015 - 00:13:53 EST

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:


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);

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

This happens when buffers are allocated with __GFP_DMA32 or

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);
pages = vzalloc(array_size);
if (!pages)

Looks sensible to me:

Acked-by: Will Deacon <will.deacon@xxxxxxx>

Thanks! I will amend the commit message and resend.
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