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

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Message-ID: <20160223152353.GA22447@lnxrabinv.se.axis.com>
Date:	Tue, 23 Feb 2016 16:23:53 +0100
From:	Rabin Vincent <rabin@....in>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Rabin Vincent <rabin.vincent@...s.com>, 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 02:06:00PM +0000, Russell King - ARM Linux wrote:
> 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.

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