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

[Christoph Hellwig]

On Tue, Sep 15, 2020 at 04:46:17PM -0400, Thomas Tai wrote:
> I tried out the suggested changes, and it successfully warned the null 
> pointer without panic. I notice that there are some places outside the 
> dma-direct, which calls dma_capable().
>
> https://elixir.bootlin.com/linux/v5.9-rc5/source/arch/x86/kernel/amd_gart_64.c#L187
>
> https://elixir.bootlin.com/linux/v5.9-rc5/source/drivers/xen/swiotlb-xen.c#L387

All of these still come in throught the wrappers in kernel/dma/mapping.c.

> Given that the WARN_ON_ONCE already did the intended warning, would you be 
> ok that I keep the null checking in dma_capable()?

No, the generic dma mapping layer is the right place.