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

[Thomas Tai]

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