1 /* 2 * Copyright (C) 2014 Red Hat 3 * Author: Rob Clark <robdclark@gmail.com> 4 * 5 * Permission is hereby granted, free of charge, to any person obtaining a 6 * copy of this software and associated documentation files (the "Software"), 7 * to deal in the Software without restriction, including without limitation 8 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 9 * and/or sell copies of the Software, and to permit persons to whom the 10 * Software is furnished to do so, subject to the following conditions: 11 * 12 * The above copyright notice and this permission notice shall be included in 13 * all copies or substantial portions of the Software. 14 * 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 18 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR 19 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, 20 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR 21 * OTHER DEALINGS IN THE SOFTWARE. 22 */ 23 24 #include <drm/drmP.h> 25 #include <drm/drm_crtc.h> 26 #include <drm/drm_modeset_lock.h> 27 28 /** 29 * DOC: kms locking 30 * 31 * As KMS moves toward more fine grained locking, and atomic ioctl where 32 * userspace can indirectly control locking order, it becomes necessary 33 * to use ww_mutex and acquire-contexts to avoid deadlocks. But because 34 * the locking is more distributed around the driver code, we want a bit 35 * of extra utility/tracking out of our acquire-ctx. This is provided 36 * by drm_modeset_lock / drm_modeset_acquire_ctx. 37 * 38 * For basic principles of ww_mutex, see: Documentation/locking/ww-mutex-design.txt 39 * 40 * The basic usage pattern is to: 41 * 42 * drm_modeset_acquire_init(&ctx) 43 * retry: 44 * foreach (lock in random_ordered_set_of_locks) { 45 * ret = drm_modeset_lock(lock, &ctx) 46 * if (ret == -EDEADLK) { 47 * drm_modeset_backoff(&ctx); 48 * goto retry; 49 * } 50 * } 51 * 52 * ... do stuff ... 53 * 54 * drm_modeset_drop_locks(&ctx); 55 * drm_modeset_acquire_fini(&ctx); 56 */ 57 58 /** 59 * drm_modeset_lock_all - take all modeset locks 60 * @dev: drm device 61 * 62 * This function takes all modeset locks, suitable where a more fine-grained 63 * scheme isn't (yet) implemented. Locks must be dropped with 64 * drm_modeset_unlock_all. 65 */ 66 void drm_modeset_lock_all(struct drm_device *dev) 67 { 68 struct drm_mode_config *config = &dev->mode_config; 69 struct drm_modeset_acquire_ctx *ctx; 70 int ret; 71 72 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 73 if (WARN_ON(!ctx)) 74 return; 75 76 mutex_lock(&config->mutex); 77 78 drm_modeset_acquire_init(ctx, 0); 79 80 retry: 81 ret = drm_modeset_lock(&config->connection_mutex, ctx); 82 if (ret) 83 goto fail; 84 ret = drm_modeset_lock_all_crtcs(dev, ctx); 85 if (ret) 86 goto fail; 87 88 WARN_ON(config->acquire_ctx); 89 90 /* now we hold the locks, so now that it is safe, stash the 91 * ctx for drm_modeset_unlock_all(): 92 */ 93 config->acquire_ctx = ctx; 94 95 drm_warn_on_modeset_not_all_locked(dev); 96 97 return; 98 99 fail: 100 if (ret == -EDEADLK) { 101 drm_modeset_backoff(ctx); 102 goto retry; 103 } 104 105 kfree(ctx); 106 } 107 EXPORT_SYMBOL(drm_modeset_lock_all); 108 109 /** 110 * drm_modeset_unlock_all - drop all modeset locks 111 * @dev: device 112 * 113 * This function drop all modeset locks taken by drm_modeset_lock_all. 114 */ 115 void drm_modeset_unlock_all(struct drm_device *dev) 116 { 117 struct drm_mode_config *config = &dev->mode_config; 118 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 119 120 if (WARN_ON(!ctx)) 121 return; 122 123 config->acquire_ctx = NULL; 124 drm_modeset_drop_locks(ctx); 125 drm_modeset_acquire_fini(ctx); 126 127 kfree(ctx); 128 129 mutex_unlock(&dev->mode_config.mutex); 130 } 131 EXPORT_SYMBOL(drm_modeset_unlock_all); 132 133 /** 134 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update 135 * @crtc: DRM CRTC 136 * @plane: DRM plane to be updated on @crtc 137 * 138 * This function locks the given crtc and plane (which should be either the 139 * primary or cursor plane) using a hidden acquire context. This is necessary so 140 * that drivers internally using the atomic interfaces can grab further locks 141 * with the lock acquire context. 142 * 143 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been 144 * converted to universal planes yet. 145 */ 146 void drm_modeset_lock_crtc(struct drm_crtc *crtc, 147 struct drm_plane *plane) 148 { 149 struct drm_modeset_acquire_ctx *ctx; 150 int ret; 151 152 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 153 if (WARN_ON(!ctx)) 154 return; 155 156 drm_modeset_acquire_init(ctx, 0); 157 158 retry: 159 ret = drm_modeset_lock(&crtc->mutex, ctx); 160 if (ret) 161 goto fail; 162 163 if (plane) { 164 ret = drm_modeset_lock(&plane->mutex, ctx); 165 if (ret) 166 goto fail; 167 168 if (plane->crtc) { 169 ret = drm_modeset_lock(&plane->crtc->mutex, ctx); 170 if (ret) 171 goto fail; 172 } 173 } 174 175 WARN_ON(crtc->acquire_ctx); 176 177 /* now we hold the locks, so now that it is safe, stash the 178 * ctx for drm_modeset_unlock_crtc(): 179 */ 180 crtc->acquire_ctx = ctx; 181 182 return; 183 184 fail: 185 if (ret == -EDEADLK) { 186 drm_modeset_backoff(ctx); 187 goto retry; 188 } 189 } 190 EXPORT_SYMBOL(drm_modeset_lock_crtc); 191 192 /** 193 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls 194 * @crtc: drm crtc 195 * 196 * Legacy ioctl operations like cursor updates or page flips only have per-crtc 197 * locking, and store the acquire ctx in the corresponding crtc. All other 198 * legacy operations take all locks and use a global acquire context. This 199 * function grabs the right one. 200 */ 201 struct drm_modeset_acquire_ctx * 202 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc) 203 { 204 if (crtc->acquire_ctx) 205 return crtc->acquire_ctx; 206 207 WARN_ON(!crtc->dev->mode_config.acquire_ctx); 208 209 return crtc->dev->mode_config.acquire_ctx; 210 } 211 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx); 212 213 /** 214 * drm_modeset_unlock_crtc - drop crtc lock 215 * @crtc: drm crtc 216 * 217 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other 218 * locks acquired through the hidden context. 219 */ 220 void drm_modeset_unlock_crtc(struct drm_crtc *crtc) 221 { 222 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx; 223 224 if (WARN_ON(!ctx)) 225 return; 226 227 crtc->acquire_ctx = NULL; 228 drm_modeset_drop_locks(ctx); 229 drm_modeset_acquire_fini(ctx); 230 231 kfree(ctx); 232 } 233 EXPORT_SYMBOL(drm_modeset_unlock_crtc); 234 235 /** 236 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 237 * @dev: device 238 * 239 * Useful as a debug assert. 240 */ 241 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 242 { 243 struct drm_crtc *crtc; 244 245 /* Locking is currently fubar in the panic handler. */ 246 if (oops_in_progress) 247 return; 248 249 drm_for_each_crtc(crtc, dev) 250 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 251 252 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 253 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 254 } 255 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 256 257 /** 258 * drm_modeset_acquire_init - initialize acquire context 259 * @ctx: the acquire context 260 * @flags: for future 261 */ 262 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 263 uint32_t flags) 264 { 265 memset(ctx, 0, sizeof(*ctx)); 266 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 267 INIT_LIST_HEAD(&ctx->locked); 268 } 269 EXPORT_SYMBOL(drm_modeset_acquire_init); 270 271 /** 272 * drm_modeset_acquire_fini - cleanup acquire context 273 * @ctx: the acquire context 274 */ 275 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 276 { 277 ww_acquire_fini(&ctx->ww_ctx); 278 } 279 EXPORT_SYMBOL(drm_modeset_acquire_fini); 280 281 /** 282 * drm_modeset_drop_locks - drop all locks 283 * @ctx: the acquire context 284 * 285 * Drop all locks currently held against this acquire context. 286 */ 287 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 288 { 289 WARN_ON(ctx->contended); 290 while (!list_empty(&ctx->locked)) { 291 struct drm_modeset_lock *lock; 292 293 lock = list_first_entry(&ctx->locked, 294 struct drm_modeset_lock, head); 295 296 drm_modeset_unlock(lock); 297 } 298 } 299 EXPORT_SYMBOL(drm_modeset_drop_locks); 300 301 static inline int modeset_lock(struct drm_modeset_lock *lock, 302 struct drm_modeset_acquire_ctx *ctx, 303 bool interruptible, bool slow) 304 { 305 int ret; 306 307 WARN_ON(ctx->contended); 308 309 if (ctx->trylock_only) { 310 lockdep_assert_held(&ctx->ww_ctx); 311 312 if (!ww_mutex_trylock(&lock->mutex)) 313 return -EBUSY; 314 else 315 return 0; 316 } else if (interruptible && slow) { 317 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 318 } else if (interruptible) { 319 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 320 } else if (slow) { 321 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 322 ret = 0; 323 } else { 324 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 325 } 326 if (!ret) { 327 WARN_ON(!list_empty(&lock->head)); 328 list_add(&lock->head, &ctx->locked); 329 } else if (ret == -EALREADY) { 330 /* we already hold the lock.. this is fine. For atomic 331 * we will need to be able to drm_modeset_lock() things 332 * without having to keep track of what is already locked 333 * or not. 334 */ 335 ret = 0; 336 } else if (ret == -EDEADLK) { 337 ctx->contended = lock; 338 } 339 340 return ret; 341 } 342 343 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, 344 bool interruptible) 345 { 346 struct drm_modeset_lock *contended = ctx->contended; 347 348 ctx->contended = NULL; 349 350 if (WARN_ON(!contended)) 351 return 0; 352 353 drm_modeset_drop_locks(ctx); 354 355 return modeset_lock(contended, ctx, interruptible, true); 356 } 357 358 /** 359 * drm_modeset_backoff - deadlock avoidance backoff 360 * @ctx: the acquire context 361 * 362 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 363 * you must call this function to drop all currently held locks and 364 * block until the contended lock becomes available. 365 */ 366 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 367 { 368 modeset_backoff(ctx, false); 369 } 370 EXPORT_SYMBOL(drm_modeset_backoff); 371 372 /** 373 * drm_modeset_backoff_interruptible - deadlock avoidance backoff 374 * @ctx: the acquire context 375 * 376 * Interruptible version of drm_modeset_backoff() 377 */ 378 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) 379 { 380 return modeset_backoff(ctx, true); 381 } 382 EXPORT_SYMBOL(drm_modeset_backoff_interruptible); 383 384 /** 385 * drm_modeset_lock - take modeset lock 386 * @lock: lock to take 387 * @ctx: acquire ctx 388 * 389 * If ctx is not NULL, then its ww acquire context is used and the 390 * lock will be tracked by the context and can be released by calling 391 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 392 * deadlock scenario has been detected and it is an error to attempt 393 * to take any more locks without first calling drm_modeset_backoff(). 394 */ 395 int drm_modeset_lock(struct drm_modeset_lock *lock, 396 struct drm_modeset_acquire_ctx *ctx) 397 { 398 if (ctx) 399 return modeset_lock(lock, ctx, false, false); 400 401 ww_mutex_lock(&lock->mutex, NULL); 402 return 0; 403 } 404 EXPORT_SYMBOL(drm_modeset_lock); 405 406 /** 407 * drm_modeset_lock_interruptible - take modeset lock 408 * @lock: lock to take 409 * @ctx: acquire ctx 410 * 411 * Interruptible version of drm_modeset_lock() 412 */ 413 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, 414 struct drm_modeset_acquire_ctx *ctx) 415 { 416 if (ctx) 417 return modeset_lock(lock, ctx, true, false); 418 419 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 420 } 421 EXPORT_SYMBOL(drm_modeset_lock_interruptible); 422 423 /** 424 * drm_modeset_unlock - drop modeset lock 425 * @lock: lock to release 426 */ 427 void drm_modeset_unlock(struct drm_modeset_lock *lock) 428 { 429 list_del_init(&lock->head); 430 ww_mutex_unlock(&lock->mutex); 431 } 432 EXPORT_SYMBOL(drm_modeset_unlock); 433 434 /* In some legacy codepaths it's convenient to just grab all the crtc and plane 435 * related locks. */ 436 int drm_modeset_lock_all_crtcs(struct drm_device *dev, 437 struct drm_modeset_acquire_ctx *ctx) 438 { 439 struct drm_crtc *crtc; 440 struct drm_plane *plane; 441 int ret = 0; 442 443 drm_for_each_crtc(crtc, dev) { 444 ret = drm_modeset_lock(&crtc->mutex, ctx); 445 if (ret) 446 return ret; 447 } 448 449 drm_for_each_plane(plane, dev) { 450 ret = drm_modeset_lock(&plane->mutex, ctx); 451 if (ret) 452 return ret; 453 } 454 455 return 0; 456 } 457 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs); 458