linux-kernel - Re: [PATCH] dma-mapping: remove an unnecessary NULL check

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Message-ID: <3142dc82-1d4c-5f01-678e-628038d86bd6@mev.co.uk>
Date:   Thu, 25 Apr 2019 15:13:49 +0100
From:   Ian Abbott <abbotti@....co.uk>
To:     Christoph Hellwig <hch@....de>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Jiri Slaby <jslaby@...e.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org,
        "kernel-janitors@...r.kernel.org H Hartley Sweeten" 
        <hsweeten@...ionengravers.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-mapping: remove an unnecessary NULL check

On 24/04/2019 15:27, Christoph Hellwig wrote:
> On Wed, Apr 24, 2019 at 05:24:37PM +0300, Dan Carpenter wrote:
>> We already dereferenced "dev" when we called get_dma_ops() so this NULL
>> check is too late.  We're not supposed to pass NULL "dev" pointers to
>> dma_alloc_attrs().
> 
> Thanks, applied to the dma-mapping for-next tree.
> 
>> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>> ---
>> There are still at least two drivers which do pass a NULL unfortunately.
>>
>> drivers/staging/comedi/drivers/comedi_isadma.c:195 comedi_isadma_alloc() error: NULL dereference inside function 'dma_alloc_coherent()'
>> drivers/staging/comedi/drivers/comedi_isadma.c:227 comedi_isadma_free() error: NULL dereference inside function 'dma_free_coherent()'
> 
> This is staging code.  Per official decree from Linus we can just
> ignore it, and I tend to do so to keep my sanity.

So for comedi_isadma, we can just replace the NULL with a pointer to a 
static dummy device with a 24-bit coherent mask?

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