Re: [PATCH] dma-direct: Fix potential NULL pointer dereference

[Christoph Hellwig]

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.