Hello Thomas Hellstrom,

The patch 667a50db0477: "drm/ttm: Refuse to fault (prime-) imported pages" from Jan 3, 2014, leads to the following static checker warning:

drivers/gpu/drm/ttm/ttm_bo_vm.c:205 ttm_bo_vm_fault() error: we previously assumed 'ttm' could be null (see line 200)

drivers/gpu/drm/ttm/ttm_bo_vm.c 133 /* 134 * Refuse to fault imported pages. This should be handled 135 * (if at all) by redirecting mmap to the exporter. 136 */ 137 if (bo->ttm && (bo->ttm->page_flags & TTM_PAGE_FLAG_SG)) { ^^^^^^^ New check for NULL. Is this really needed?

138 retval = VM_FAULT_SIGBUS; 139 goto out_unlock; 140 }

[ snip ]

188 /* 189 * Make a local vma copy to modify the page_prot member 190 * and vm_flags if necessary. The vma parameter is protected 191 * by mmap_sem in write mode. 192 */ 193 cvma = *vma; 194 cvma.vm_page_prot = vm_get_page_prot(cvma.vm_flags); 195 196 if (bo->mem.bus.is_iomem) { 197 cvma.vm_page_prot = ttm_io_prot(bo->mem.placement, 198 cvma.vm_page_prot); 199 } else { 200 ttm = bo->ttm; ^^^^^^^^^^^^^ 201 cvma.vm_page_prot = ttm_io_prot(bo->mem.placement, 202 cvma.vm_page_prot); 203 204 /* Allocate all page at once, most common usage */ 205 if (ttm->bdev->driver->ttm_tt_populate(ttm)) { ^^^^^^^^^ Old unchecked dereference.

206 retval = VM_FAULT_OOM; 207 goto out_io_unlock; 208 } 209 } 210

regards, dan carpenter