[PATCH] powerpc/iommu: avoid derefence before pointer check

[Breno Leitao]

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.

CC: Alistair Popple <alist...@popple.id.au>
Signed-off-by: Breno Leitao <lei...@debian.org>
---
 arch/powerpc/kernel/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index af7a20dc6e09..80b6caaa9b92 100644
--- 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)
-- 
2.16.3