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 /** 60 * __drm_modeset_lock_all - internal helper to grab all modeset locks 61 * @dev: DRM device 62 * @trylock: trylock mode for atomic contexts 63 * 64 * This is a special version of drm_modeset_lock_all() which can also be used in 65 * atomic contexts. Then @trylock must be set to true. 66 * 67 * Returns: 68 * 0 on success or negative error code on failure. 69 */ 70 int __drm_modeset_lock_all(struct drm_device *dev, 71 bool trylock) 72 { 73 struct drm_mode_config *config = &dev->mode_config; 74 struct drm_modeset_acquire_ctx *ctx; 75 int ret; 76 77 ctx = kzalloc(sizeof(*ctx), 78 trylock ? GFP_ATOMIC : GFP_KERNEL); 79 if (!ctx) 80 return -ENOMEM; 81 82 if (trylock) { 83 if (!mutex_trylock(&config->mutex)) 84 return -EBUSY; 85 } else { 86 mutex_lock(&config->mutex); 87 } 88 89 drm_modeset_acquire_init(ctx, 0); 90 ctx->trylock_only = trylock; 91 92 retry: 93 ret = drm_modeset_lock(&config->connection_mutex, ctx); 94 if (ret) 95 goto fail; 96 ret = drm_modeset_lock_all_crtcs(dev, ctx); 97 if (ret) 98 goto fail; 99 100 WARN_ON(config->acquire_ctx); 101 102 /* now we hold the locks, so now that it is safe, stash the 103 * ctx for drm_modeset_unlock_all(): 104 */ 105 config->acquire_ctx = ctx; 106 107 drm_warn_on_modeset_not_all_locked(dev); 108 109 return 0; 110 111 fail: 112 if (ret == -EDEADLK) { 113 drm_modeset_backoff(ctx); 114 goto retry; 115 } 116 117 return ret; 118 } 119 EXPORT_SYMBOL(__drm_modeset_lock_all); 120 121 /** 122 * drm_modeset_lock_all - take all modeset locks 123 * @dev: drm device 124 * 125 * This function takes all modeset locks, suitable where a more fine-grained 126 * scheme isn't (yet) implemented. Locks must be dropped with 127 * drm_modeset_unlock_all. 128 */ 129 void drm_modeset_lock_all(struct drm_device *dev) 130 { 131 WARN_ON(__drm_modeset_lock_all(dev, false) != 0); 132 } 133 EXPORT_SYMBOL(drm_modeset_lock_all); 134 135 /** 136 * drm_modeset_unlock_all - drop all modeset locks 137 * @dev: device 138 * 139 * This function drop all modeset locks taken by drm_modeset_lock_all. 140 */ 141 void drm_modeset_unlock_all(struct drm_device *dev) 142 { 143 struct drm_mode_config *config = &dev->mode_config; 144 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 145 146 if (WARN_ON(!ctx)) 147 return; 148 149 config->acquire_ctx = NULL; 150 drm_modeset_drop_locks(ctx); 151 drm_modeset_acquire_fini(ctx); 152 153 kfree(ctx); 154 155 mutex_unlock(&dev->mode_config.mutex); 156 } 157 EXPORT_SYMBOL(drm_modeset_unlock_all); 158 159 /** 160 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update 161 * @crtc: DRM CRTC 162 * @plane: DRM plane to be updated on @crtc 163 * 164 * This function locks the given crtc and plane (which should be either the 165 * primary or cursor plane) using a hidden acquire context. This is necessary so 166 * that drivers internally using the atomic interfaces can grab further locks 167 * with the lock acquire context. 168 * 169 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been 170 * converted to universal planes yet. 171 */ 172 void drm_modeset_lock_crtc(struct drm_crtc *crtc, 173 struct drm_plane *plane) 174 { 175 struct drm_modeset_acquire_ctx *ctx; 176 int ret; 177 178 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 179 if (WARN_ON(!ctx)) 180 return; 181 182 drm_modeset_acquire_init(ctx, 0); 183 184 retry: 185 ret = drm_modeset_lock(&crtc->mutex, ctx); 186 if (ret) 187 goto fail; 188 189 if (plane) { 190 ret = drm_modeset_lock(&plane->mutex, ctx); 191 if (ret) 192 goto fail; 193 194 if (plane->crtc) { 195 ret = drm_modeset_lock(&plane->crtc->mutex, ctx); 196 if (ret) 197 goto fail; 198 } 199 } 200 201 WARN_ON(crtc->acquire_ctx); 202 203 /* now we hold the locks, so now that it is safe, stash the 204 * ctx for drm_modeset_unlock_crtc(): 205 */ 206 crtc->acquire_ctx = ctx; 207 208 return; 209 210 fail: 211 if (ret == -EDEADLK) { 212 drm_modeset_backoff(ctx); 213 goto retry; 214 } 215 } 216 EXPORT_SYMBOL(drm_modeset_lock_crtc); 217 218 /** 219 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls 220 * @crtc: drm crtc 221 * 222 * Legacy ioctl operations like cursor updates or page flips only have per-crtc 223 * locking, and store the acquire ctx in the corresponding crtc. All other 224 * legacy operations take all locks and use a global acquire context. This 225 * function grabs the right one. 226 */ 227 struct drm_modeset_acquire_ctx * 228 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc) 229 { 230 if (crtc->acquire_ctx) 231 return crtc->acquire_ctx; 232 233 WARN_ON(!crtc->dev->mode_config.acquire_ctx); 234 235 return crtc->dev->mode_config.acquire_ctx; 236 } 237 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx); 238 239 /** 240 * drm_modeset_unlock_crtc - drop crtc lock 241 * @crtc: drm crtc 242 * 243 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other 244 * locks acquired through the hidden context. 245 */ 246 void drm_modeset_unlock_crtc(struct drm_crtc *crtc) 247 { 248 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx; 249 250 if (WARN_ON(!ctx)) 251 return; 252 253 crtc->acquire_ctx = NULL; 254 drm_modeset_drop_locks(ctx); 255 drm_modeset_acquire_fini(ctx); 256 257 kfree(ctx); 258 } 259 EXPORT_SYMBOL(drm_modeset_unlock_crtc); 260 261 /** 262 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 263 * @dev: device 264 * 265 * Useful as a debug assert. 266 */ 267 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 268 { 269 struct drm_crtc *crtc; 270 271 /* Locking is currently fubar in the panic handler. */ 272 if (oops_in_progress) 273 return; 274 275 list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) 276 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 277 278 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 279 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 280 } 281 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 282 283 /** 284 * drm_modeset_acquire_init - initialize acquire context 285 * @ctx: the acquire context 286 * @flags: for future 287 */ 288 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 289 uint32_t flags) 290 { 291 memset(ctx, 0, sizeof(*ctx)); 292 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 293 INIT_LIST_HEAD(&ctx->locked); 294 } 295 EXPORT_SYMBOL(drm_modeset_acquire_init); 296 297 /** 298 * drm_modeset_acquire_fini - cleanup acquire context 299 * @ctx: the acquire context 300 */ 301 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 302 { 303 ww_acquire_fini(&ctx->ww_ctx); 304 } 305 EXPORT_SYMBOL(drm_modeset_acquire_fini); 306 307 /** 308 * drm_modeset_drop_locks - drop all locks 309 * @ctx: the acquire context 310 * 311 * Drop all locks currently held against this acquire context. 312 */ 313 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 314 { 315 WARN_ON(ctx->contended); 316 while (!list_empty(&ctx->locked)) { 317 struct drm_modeset_lock *lock; 318 319 lock = list_first_entry(&ctx->locked, 320 struct drm_modeset_lock, head); 321 322 drm_modeset_unlock(lock); 323 } 324 } 325 EXPORT_SYMBOL(drm_modeset_drop_locks); 326 327 static inline int modeset_lock(struct drm_modeset_lock *lock, 328 struct drm_modeset_acquire_ctx *ctx, 329 bool interruptible, bool slow) 330 { 331 int ret; 332 333 WARN_ON(ctx->contended); 334 335 if (ctx->trylock_only) { 336 if (!ww_mutex_trylock(&lock->mutex)) 337 return -EBUSY; 338 else 339 return 0; 340 } else if (interruptible && slow) { 341 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 342 } else if (interruptible) { 343 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 344 } else if (slow) { 345 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 346 ret = 0; 347 } else { 348 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 349 } 350 if (!ret) { 351 WARN_ON(!list_empty(&lock->head)); 352 list_add(&lock->head, &ctx->locked); 353 } else if (ret == -EALREADY) { 354 /* we already hold the lock.. this is fine. For atomic 355 * we will need to be able to drm_modeset_lock() things 356 * without having to keep track of what is already locked 357 * or not. 358 */ 359 ret = 0; 360 } else if (ret == -EDEADLK) { 361 ctx->contended = lock; 362 } 363 364 return ret; 365 } 366 367 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, 368 bool interruptible) 369 { 370 struct drm_modeset_lock *contended = ctx->contended; 371 372 ctx->contended = NULL; 373 374 if (WARN_ON(!contended)) 375 return 0; 376 377 drm_modeset_drop_locks(ctx); 378 379 return modeset_lock(contended, ctx, interruptible, true); 380 } 381 382 /** 383 * drm_modeset_backoff - deadlock avoidance backoff 384 * @ctx: the acquire context 385 * 386 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 387 * you must call this function to drop all currently held locks and 388 * block until the contended lock becomes available. 389 */ 390 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 391 { 392 modeset_backoff(ctx, false); 393 } 394 EXPORT_SYMBOL(drm_modeset_backoff); 395 396 /** 397 * drm_modeset_backoff_interruptible - deadlock avoidance backoff 398 * @ctx: the acquire context 399 * 400 * Interruptible version of drm_modeset_backoff() 401 */ 402 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) 403 { 404 return modeset_backoff(ctx, true); 405 } 406 EXPORT_SYMBOL(drm_modeset_backoff_interruptible); 407 408 /** 409 * drm_modeset_lock - take modeset lock 410 * @lock: lock to take 411 * @ctx: acquire ctx 412 * 413 * If ctx is not NULL, then its ww acquire context is used and the 414 * lock will be tracked by the context and can be released by calling 415 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 416 * deadlock scenario has been detected and it is an error to attempt 417 * to take any more locks without first calling drm_modeset_backoff(). 418 */ 419 int drm_modeset_lock(struct drm_modeset_lock *lock, 420 struct drm_modeset_acquire_ctx *ctx) 421 { 422 if (ctx) 423 return modeset_lock(lock, ctx, false, false); 424 425 ww_mutex_lock(&lock->mutex, NULL); 426 return 0; 427 } 428 EXPORT_SYMBOL(drm_modeset_lock); 429 430 /** 431 * drm_modeset_lock_interruptible - take modeset lock 432 * @lock: lock to take 433 * @ctx: acquire ctx 434 * 435 * Interruptible version of drm_modeset_lock() 436 */ 437 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, 438 struct drm_modeset_acquire_ctx *ctx) 439 { 440 if (ctx) 441 return modeset_lock(lock, ctx, true, false); 442 443 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 444 } 445 EXPORT_SYMBOL(drm_modeset_lock_interruptible); 446 447 /** 448 * drm_modeset_unlock - drop modeset lock 449 * @lock: lock to release 450 */ 451 void drm_modeset_unlock(struct drm_modeset_lock *lock) 452 { 453 list_del_init(&lock->head); 454 ww_mutex_unlock(&lock->mutex); 455 } 456 EXPORT_SYMBOL(drm_modeset_unlock); 457 458 /* In some legacy codepaths it's convenient to just grab all the crtc and plane 459 * related locks. */ 460 int drm_modeset_lock_all_crtcs(struct drm_device *dev, 461 struct drm_modeset_acquire_ctx *ctx) 462 { 463 struct drm_mode_config *config = &dev->mode_config; 464 struct drm_crtc *crtc; 465 struct drm_plane *plane; 466 int ret = 0; 467 468 list_for_each_entry(crtc, &config->crtc_list, head) { 469 ret = drm_modeset_lock(&crtc->mutex, ctx); 470 if (ret) 471 return ret; 472 } 473 474 list_for_each_entry(plane, &config->plane_list, head) { 475 ret = drm_modeset_lock(&plane->mutex, ctx); 476 if (ret) 477 return ret; 478 } 479 480 return 0; 481 } 482 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs); 483