drm/radeon: fix AGP userptr handling

[Dan Carpenter]

Hello Christian K?nig,

This is a semi-automatic email about new static checker warnings.

The patch 3840a656f61f: "drm/radeon: fix AGP userptr handling" from 
Sep 17, 2014, leads to the following Smatch complaint:

drivers/gpu/drm/radeon/radeon_ttm.c:708 radeon_ttm_tt_populate()
         error: we previously assumed 'gtt' could be null (see line 696)

drivers/gpu/drm/radeon/radeon_ttm.c
   695  
   696          if (gtt && gtt->userptr) {
                    ^^^
New check.

   697                  ttm->sg = kcalloc(1, sizeof(struct sg_table), 
GFP_KERNEL);
   698                  if (!ttm->sg)
   699                          return -ENOMEM;
   700  
   701                  ttm->page_flags |= TTM_PAGE_FLAG_SG;
   702                  ttm->state = tt_unbound;
   703                  return 0;
   704          }
   705  
   706          if (slave && ttm->sg) {
   707                  drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
   708                                                   gtt->ttm.dma_address, 
ttm->num_pages);
                                                         ^^^^^^^^
Old unchecked dereference.

   709                  ttm->state = tt_unbound;
   710                  return 0;


drivers/gpu/drm/radeon/radeon_ttm.c
   754  
   755          if (gtt && gtt->userptr) {
                    ^^^
   756                  kfree(ttm->sg);
   757                  ttm->page_flags &= ~TTM_PAGE_FLAG_SG;
   758                  return;
   759          }
   760  
   761          if (slave)
   762                  return;
   763  
   764          rdev = radeon_get_rdev(ttm->bdev);
   765  #if __OS_HAS_AGP
   766          if (rdev->flags & RADEON_IS_AGP) {
   767                  ttm_agp_tt_unpopulate(ttm);
   768                  return;
   769          }
   770  #endif
   771  
   772  #ifdef CONFIG_SWIOTLB
   773          if (swiotlb_nr_tbl()) {
   774                  ttm_dma_unpopulate(&gtt->ttm, rdev->dev);
   775                  return;
   776          }
   777  #endif
   778  
   779          for (i = 0; i < ttm->num_pages; i++) {
   780                  if (gtt->ttm.dma_address[i]) {
                            ^^^^^^^^
   781                          pci_unmap_page(rdev->pdev, 
gtt->ttm.dma_address[i],
   782                                         PAGE_SIZE, 
PCI_DMA_BIDIRECTIONAL);

regards,
dan carpenter