Suppose:
CONFIG_SPARSEMEM is opened.
CONFIG_DMA_API_DEBUG or CONFIG_CMA is opened.
Then virt_to_page or phys_to_page will be called. Finally, in __pfn_to_page,
__sec = __pfn_to_section(__pfn) is NULL.
So access section->section_mem_map will trigger exception.
---------
#define __pfn_to_page(pfn) \
({ unsigned long __pfn = (pfn); \
struct mem_section *__sec = __pfn_to_section(__pfn); \
__section_mem_map_addr(__sec) + __pfn; \
})
static inline struct page *__section_mem_map_addr(struct mem_section *section)
{
unsigned long map = section->section_mem_map;
map &= SECTION_MAP_MASK;
return (struct page *)map;
}
On 2016/3/7 17:21, Zhen Lei wrote:
> Do this to keep consistent with kfree, which tolerate ptr is NULL.
>
> Signed-off-by: Zhen Lei <thunder.leiz...@huawei.com>
> ---
> include/linux/dma-mapping.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 75857cd..fdd4294 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -402,7 +402,10 @@ static inline void *dma_alloc_coherent(struct device
> *dev, size_t size,
> static inline void dma_free_coherent(struct device *dev, size_t size,
> void *cpu_addr, dma_addr_t dma_handle)
> {
> - return dma_free_attrs(dev, size, cpu_addr, dma_handle, NULL);
> + if (unlikely(!cpu_addr))
> + return;
> +
> + dma_free_attrs(dev, size, cpu_addr, dma_handle, NULL);
> }
>
> static inline void *dma_alloc_noncoherent(struct device *dev, size_t size,
> --
> 2.5.0
>
>
>
> .
>
