linux-kernel - Re: [BUG][PATCH]dma-coherent.c: error path bug

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Message-Id: <201006070708.57453.mitov@issp.bas.bg>
Date:	Mon, 7 Jun 2010 07:08:56 +0300
From:	Marin Mitov <mitov@...p.bas.bg>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [BUG][PATCH]dma-coherent.c: error path bug

On Monday, June 07, 2010 05:30:48 am FUJITA Tomonori wrote:
> On Sun, 6 Jun 2010 13:53:04 +0300
> Marin Mitov <mitov@...p.bas.bg> wrote:
> 
> > Hi all,
> > 
> > The error path in dma_declare_coherent_memory() leaves 
> > the pointer dev->dma_mem non completely initialized.
> > 
> > If allocation of dev->dma_mem succeeds, 
> > but allocation of dev->dma_mem->bitmap fails
> > dev->dma_mem is freed, but left non NULL
> > and non completely initialized.
> > 
> > Either zero it after being freed (one liner patch), or assign to 
> > dev->dma_mem only completely initialized structure (patch included).
> > 
> > Comments welcome.
> > 
> > Marin Mitov
> > 
> > Signed-off-by: Marin Mitov <mitov@...p.bas.bg>
> 
> Hmm, if dma_declare_coherent_memory() fails, the driver doesn't use
> dev->dma_mem. So even if dev->dma_mem points to a freed memory, I'm
> not sure that it causes a real problem. We could call this patch a
> cleanup though.
> 
My understanding of dma_alloc_coherent() is that  we first try to allocate from 
per-device coherent memory and we do it using dma_alloc_from_coherent()
(in drivers/base/dma-coherent.c) if dev->dma_mem is not NULL (and we have 
left it not NULL, here is the problem). If allocation of dev->dma_mem->bitmap 
fails dev->dma_mem must be NULL.

Marin Mitov

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