linux-kernel - Re: [PATCH 2/2] ARM: dma-mapping: fix alloc/free for coherent + CMA + gfp=0

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Message-ID: <20160219140600.GW19428@n2100.arm.linux.org.uk>
Date:	Fri, 19 Feb 2016 14:06:00 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Rabin Vincent <rabin.vincent@...s.com>
Cc:	mina86@...a86.com, akpm@...ux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Rabin Vincent <rabinv@...s.com>
Subject: Re: [PATCH 2/2] ARM: dma-mapping: fix alloc/free for coherent + CMA
 + gfp=0

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

Maybe someone can put some thought into this...

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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