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 0 247 if (oops_in_progress) 248 return; 249 #endif 250 251 drm_for_each_crtc(crtc, dev) 252 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 253 254 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 255 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 256 } 257 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 258 259 /** 260 * drm_modeset_acquire_init - initialize acquire context 261 * @ctx: the acquire context 262 * @flags: for future 263 */ 264 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 265 uint32_t flags) 266 { 267 memset(ctx, 0, sizeof(*ctx)); 268 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 269 INIT_LIST_HEAD(&ctx->locked); 270 } 271 EXPORT_SYMBOL(drm_modeset_acquire_init); 272 273 /** 274 * drm_modeset_acquire_fini - cleanup acquire context 275 * @ctx: the acquire context 276 */ 277 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 278 { 279 ww_acquire_fini(&ctx->ww_ctx); 280 } 281 EXPORT_SYMBOL(drm_modeset_acquire_fini); 282 283 /** 284 * drm_modeset_drop_locks - drop all locks 285 * @ctx: the acquire context 286 * 287 * Drop all locks currently held against this acquire context. 288 */ 289 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 290 { 291 WARN_ON(ctx->contended); 292 while (!list_empty(&ctx->locked)) { 293 struct drm_modeset_lock_info *info; 294 295 info = list_first_entry(&ctx->locked, 296 struct drm_modeset_lock_info, ctx_entry); 297 298 drm_modeset_unlock(info->lock); 299 } 300 } 301 EXPORT_SYMBOL(drm_modeset_drop_locks); 302 303 static inline int modeset_lock(struct drm_modeset_lock *lock, 304 struct drm_modeset_acquire_ctx *ctx, 305 bool interruptible, bool slow) 306 { 307 int ret; 308 309 WARN_ON(ctx->contended); 310 311 if (ctx->trylock_only) { 312 #if 0 313 lockdep_assert_held(&ctx->ww_ctx); 314 #endif 315 316 if (!ww_mutex_trylock(&lock->mutex)) 317 return -EBUSY; 318 else 319 return 0; 320 } else if (interruptible && slow) { 321 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 322 } else if (interruptible) { 323 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 324 } else if (slow) { 325 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 326 ret = 0; 327 } else { 328 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 329 } 330 if (ret == -EALREADY) { 331 /* we already hold the lock.. this is fine. For atomic 332 * we will need to be able to drm_modeset_lock() things 333 * without having to keep track of what is already locked 334 * or not. 335 */ 336 ret = 0; 337 } else if (ret == -EDEADLK) { 338 ctx->contended = lock; 339 } 340 if (ret == 0) { 341 struct drm_modeset_lock_info *info; 342 343 info = kzalloc(sizeof(*info), GFP_KERNEL); 344 INIT_LIST_HEAD(&info->ctx_entry); 345 INIT_LIST_HEAD(&info->lock_entry); 346 info->lock = lock; 347 info->ctx = ctx; 348 list_add(&info->ctx_entry, &ctx->locked); 349 list_add(&info->lock_entry, &lock->locked); 350 } 351 352 return ret; 353 } 354 355 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, 356 bool interruptible) 357 { 358 struct drm_modeset_lock *contended = ctx->contended; 359 360 ctx->contended = NULL; 361 362 if (WARN_ON(!contended)) 363 return 0; 364 365 drm_modeset_drop_locks(ctx); 366 367 return modeset_lock(contended, ctx, interruptible, true); 368 } 369 370 /** 371 * drm_modeset_backoff - deadlock avoidance backoff 372 * @ctx: the acquire context 373 * 374 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 375 * you must call this function to drop all currently held locks and 376 * block until the contended lock becomes available. 377 */ 378 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 379 { 380 modeset_backoff(ctx, false); 381 } 382 EXPORT_SYMBOL(drm_modeset_backoff); 383 384 /** 385 * drm_modeset_backoff_interruptible - deadlock avoidance backoff 386 * @ctx: the acquire context 387 * 388 * Interruptible version of drm_modeset_backoff() 389 */ 390 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) 391 { 392 return modeset_backoff(ctx, true); 393 } 394 EXPORT_SYMBOL(drm_modeset_backoff_interruptible); 395 396 /** 397 * drm_modeset_lock - take modeset lock 398 * @lock: lock to take 399 * @ctx: acquire ctx 400 * 401 * If ctx is not NULL, then its ww acquire context is used and the 402 * lock will be tracked by the context and can be released by calling 403 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 404 * deadlock scenario has been detected and it is an error to attempt 405 * to take any more locks without first calling drm_modeset_backoff(). 406 */ 407 int drm_modeset_lock(struct drm_modeset_lock *lock, 408 struct drm_modeset_acquire_ctx *ctx) 409 { 410 if (ctx) 411 return modeset_lock(lock, ctx, false, false); 412 413 ww_mutex_lock(&lock->mutex, NULL); 414 return 0; 415 } 416 EXPORT_SYMBOL(drm_modeset_lock); 417 418 /** 419 * drm_modeset_lock_interruptible - take modeset lock 420 * @lock: lock to take 421 * @ctx: acquire ctx 422 * 423 * Interruptible version of drm_modeset_lock() 424 */ 425 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, 426 struct drm_modeset_acquire_ctx *ctx) 427 { 428 if (ctx) 429 return modeset_lock(lock, ctx, true, false); 430 431 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 432 } 433 EXPORT_SYMBOL(drm_modeset_lock_interruptible); 434 435 /** 436 * drm_modeset_unlock - drop modeset lock 437 * @lock: lock to release 438 */ 439 void drm_modeset_unlock(struct drm_modeset_lock *lock) 440 { 441 struct drm_modeset_lock_info *info; 442 443 /* undo in reverse order */ 444 if (!list_empty(&lock->locked)) { 445 info = list_last_entry(&lock->locked, 446 struct drm_modeset_lock_info, lock_entry); 447 list_del_init(&info->lock_entry); 448 if (info->ctx) 449 list_del_init(&info->ctx_entry); 450 kfree(info); 451 } 452 ww_mutex_unlock(&lock->mutex); 453 } 454 EXPORT_SYMBOL(drm_modeset_unlock); 455 456 /* In some legacy codepaths it's convenient to just grab all the crtc and plane 457 * related locks. */ 458 int drm_modeset_lock_all_crtcs(struct drm_device *dev, 459 struct drm_modeset_acquire_ctx *ctx) 460 { 461 struct drm_crtc *crtc; 462 struct drm_plane *plane; 463 int ret = 0; 464 465 drm_for_each_crtc(crtc, dev) { 466 ret = drm_modeset_lock(&crtc->mutex, ctx); 467 if (ret) 468 return ret; 469 } 470 471 drm_for_each_plane(plane, dev) { 472 ret = drm_modeset_lock(&plane->mutex, ctx); 473 if (ret) 474 return ret; 475 } 476 477 return 0; 478 } 479 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs); 480