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Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference
To:     Christoph Hellwig <hch@lst.de>
Cc:     konrad.wilk@oracle.com, m.szyprowski@samsung.com,
        robin.murphy@arm.com, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
References: <1600178594-22801-1-git-send-email-thomas.tai@oracle.com>
 <20200915140719.GA14831@lst.de>
 <f5cba632-421a-f375-3697-51a182a53a32@oracle.com>
 <20200915142624.GA16005@lst.de>
 <da9ec51d-aab5-695d-e388-5ae7c0bb30ea@oracle.com>
 <20200915150929.GA19770@lst.de>
From:   Thomas Tai <thomas.tai@oracle.com>
Message-ID: <9a819530-365b-9982-c9c9-ad20d6c8149e@oracle.com>
Date:   Tue, 15 Sep 2020 11:12:28 -0400
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On 2020-09-15 11:09 a.m., Christoph Hellwig wrote:
> On Tue, Sep 15, 2020 at 10:40:39AM -0400, Thomas Tai wrote:
>>> +++ b/include/linux/dma-direct.h
>>> @@ -62,9 +62,6 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
>>>    {
>>>    	dma_addr_t end = addr + size - 1;
>>>    -	if (!dev->dma_mask)
>>> -		return false;
>>> -
>>
>> I am concerned that some drivers may rely on this NULL checking. Would you
>> think we can keep this checking and use the following WARN_ON_ONCE()?
> 
> dma_capable is not a helper for drivers, but just for dma-direct
> and related code.  And this patch adds the checks for the three
> places how we call into the ->map* methods.
> 

Ok. That sounds good to me. I will make the suggested changes and run 
some tests before sending out the V2 patch.

Thank you,
Thomas