Hi,

Static analysis with Coverity on Linux-next has detected a potential issue with the following commit:

commit 480ae79537b28f30ef6e07b7de69a9ae2599daa7 Author: Maarten Lankhorst maarten.lankhorst@linux.intel.com Date: Tue Mar 23 16:50:49 2021 +0100

drm/i915/selftests: Prepare gtt tests for obj->mm.lock removal

The analysis by Coverity is as follows:

145 static int igt_ppgtt_alloc(void *arg) 146 { 147 struct drm_i915_private *dev_priv = arg; 148 struct i915_ppgtt *ppgtt; 1. var_decl: Declaring variable ww without initializer. 149 struct i915_gem_ww_ctx ww; 150 u64 size, last, limit; 151 int err = 0; 152 153 /* Allocate a ppggt and try to fill the entire range */ 154 2. Condition !(dev_priv->__info.ppgtt_type != INTEL_PPGTT_NONE), taking false branch. 155 if (!HAS_PPGTT(dev_priv)) 156 return 0; 157 158 ppgtt = i915_ppgtt_create(&dev_priv->gt); 3. Condition IS_ERR(ppgtt), taking false branch. 159 if (IS_ERR(ppgtt)) 160 return PTR_ERR(ppgtt); 161 4. Condition !ppgtt->vm.allocate_va_range, taking true branch. 162 if (!ppgtt->vm.allocate_va_range) 5. Jumping to label err_ppgtt_cleanup. 163 goto err_ppgtt_cleanup; 164 165 /* 166 * While we only allocate the page tables here and so we could 167 * address a much larger GTT than we could actually fit into 168 * RAM, a practical limit is the amount of physical pages in the system. 169 * This should ensure that we do not run into the oomkiller during 170 * the test and take down the machine wilfully. 171 */ 172 limit = totalram_pages() << PAGE_SHIFT; 173 limit = min(ppgtt->vm.total, limit); 174 175 i915_gem_ww_ctx_init(&ww, false); 176retry: 177 err = i915_vm_lock_objects(&ppgtt->vm, &ww); 178 if (err) 179 goto err_ppgtt_cleanup; 180 181 /* Check we can allocate the entire range */ 182 for (size = 4096; size <= limit; size <<= 2) { 183 struct i915_vm_pt_stash stash = {}; 184 185 err = i915_vm_alloc_pt_stash(&ppgtt->vm, &stash, size); 186 if (err) 187 goto err_ppgtt_cleanup; 188 189 err = i915_vm_pin_pt_stash(&ppgtt->vm, &stash); 190 if (err) { 191 i915_vm_free_pt_stash(&ppgtt->vm, &stash); 192 goto err_ppgtt_cleanup; 193 } 194 195 ppgtt->vm.allocate_va_range(&ppgtt->vm, &stash, 0, size); 196 cond_resched(); 197 198 ppgtt->vm.clear_range(&ppgtt->vm, 0, size); 199 200 i915_vm_free_pt_stash(&ppgtt->vm, &stash); 201 } 202 203 /* Check we can incrementally allocate the entire range */ 204 for (last = 0, size = 4096; size <= limit; last = size, size <<= 2) { 205 struct i915_vm_pt_stash stash = {}; 206 207 err = i915_vm_alloc_pt_stash(&ppgtt->vm, &stash, size - last); 208 if (err) 209 goto err_ppgtt_cleanup; 210 211 err = i915_vm_pin_pt_stash(&ppgtt->vm, &stash); 212 if (err) { 213 i915_vm_free_pt_stash(&ppgtt->vm, &stash); 214 goto err_ppgtt_cleanup; 215 } 216 217 ppgtt->vm.allocate_va_range(&ppgtt->vm, &stash, 218 last, size - last); 219 cond_resched(); 220 221 i915_vm_free_pt_stash(&ppgtt->vm, &stash); 222 } 223 224 err_ppgtt_cleanup: 6. Condition err == -35, taking false branch. 225 if (err == -EDEADLK) { 226 err = i915_gem_ww_ctx_backoff(&ww); 227 if (!err) 228 goto retry; 229 } 7. uninit_use_in_call: Using uninitialized value ww.contended when calling i915_gem_ww_ctx_fini. Uninitialized pointer read (UNINIT) 8. uninit_use_in_call: Using uninitialized value ww.ctx.acquired when calling i915_gem_ww_ctx_fini. 230 i915_gem_ww_ctx_fini(&ww); 231 232 i915_vm_put(&ppgtt->vm); 233 return err; 234 }

Coverity is reporting use of uninitialized values in (lines 230. Not sure what the best fix is for this, so I'm reporting this as a potential issue.

Colin