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

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Date:   Tue, 15 Sep 2020 16:08:30 +0200
From:   Christoph Hellwig <hch@....de>
To:     Thomas Tai <thomas.tai@...cle.com>
Cc:     konrad.wilk@...cle.com, m.szyprowski@...sung.com, hch@....de,
        robin.murphy@....com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference

On Tue, Sep 15, 2020 at 04:07:19PM +0200, Christoph Hellwig wrote:
> On Tue, Sep 15, 2020 at 08:03:14AM -0600, Thomas Tai wrote:
> > When booting the kernel v5.9-rc4 on a VM, the kernel would panic when
> > printing a warning message in swiotlb_map(). It is because dev->dma_mask
> > can potentially be a null pointer. Using the dma_get_mask() macro can
> > avoid the NULL pointer dereference.
> 
> dma_mask must not be zero.  This means drm is calling DMA API functions
> on something weird.  This needs to be fixed in the caller.

s/zero/NULL/, but the point stands.