powerpc/iommu: Avoid derefence before pointer check

The tbl pointer is being derefenced by IOMMU_PAGE_SIZE prior the check
if it is not NULL.

Just moving the dereference code to after the check, where there will
be guarantee that 'tbl' will not be NULL.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index af7a20d..80b6caa 100644 (file)
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -785,9 +785,9 @@ dma_addr_t iommu_map_page(struct device *dev, struct iommu_table *tbl,
 
        vaddr = page_address(page) + offset;
        uaddr = (unsigned long)vaddr;
-       npages = iommu_num_pages(uaddr, size, IOMMU_PAGE_SIZE(tbl));
 
        if (tbl) {
+               npages = iommu_num_pages(uaddr, size, IOMMU_PAGE_SIZE(tbl));
                align = 0;
                if (tbl->it_page_shift < PAGE_SHIFT && size >= PAGE_SIZE &&
                    ((unsigned long)vaddr & ~PAGE_MASK) == 0)