On Fri, Feb 19, 2016 at 02:06:00PM +0000, Russell King - ARM Linux wrote:

On Fri, Feb 19, 2016 at 09:12:04AM +0100, Rabin Vincent wrote:

quoted

Given a device which uses arm_coherent_dma_ops and on which
dev_get_cma_area(dev) returns non-NULL, the following usage of the DMA
API with gfp=0 results in a memory leak and memory corruption.

 p = dma_alloc_coherent(dev, sz, &dma, 0);
 if (p)
 	dma_free_coherent(dev, sz, p, dma);

The memory leak is because the alloc allocates using
__alloc_simple_buffer() but the free attempts
dma_release_from_contiguous(), which does not do free anything since the
page is not in the CMA area.

I'd really like to see a better solution to this problem: over the course
of the years, I've seen a number of patches that rearrange the test order
at allocation time because of some problem or the other.

What we need is a better way to ensure that we use the correct release
functionality - having two independent set of tests where the order
matters is really not very good.

I've sent a v2 of this series which refactors the code so that we no
longer have two independent sets of tests.