On 2020-09-15 10:07 a.m., 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.


Thanks, Christoph for your comment. The caller already fixed the null pointer in the latest v5.9-rc5. I am thinking that if we had used the dma_get_mask(), the kernel couldn't panic and could properly print out the warning message.

Thomas
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