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 &struct drm_modeset_lock and &struct 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 * ... do stuff ... 52 * drm_modeset_drop_locks(&ctx); 53 * drm_modeset_acquire_fini(&ctx); 54 * 55 * On top of of these per-object locks using &ww_mutex there's also an overall 56 * &drm_mode_config.mutex, for protecting everything else. Mostly this means 57 * probe state of connectors, and preventing hotplug add/removal of connectors. 58 * 59 * Finally there's a bunch of dedicated locks to protect drm core internal 60 * lists and lookup data structures. 61 */ 62 63 static DEFINE_WW_CLASS(crtc_ww_class); 64 65 /** 66 * drm_modeset_lock_all - take all modeset locks 67 * @dev: DRM device 68 * 69 * This function takes all modeset locks, suitable where a more fine-grained 70 * scheme isn't (yet) implemented. Locks must be dropped by calling the 71 * drm_modeset_unlock_all() function. 72 * 73 * This function is deprecated. It allocates a lock acquisition context and 74 * stores it in &drm_device.mode_config. This facilitate conversion of 75 * existing code because it removes the need to manually deal with the 76 * acquisition context, but it is also brittle because the context is global 77 * and care must be taken not to nest calls. New code should use the 78 * drm_modeset_lock_all_ctx() function and pass in the context explicitly. 79 */ 80 void drm_modeset_lock_all(struct drm_device *dev) 81 { 82 struct drm_mode_config *config = &dev->mode_config; 83 struct drm_modeset_acquire_ctx *ctx; 84 int ret; 85 86 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 87 if (WARN_ON(!ctx)) 88 return; 89 90 mutex_lock(&config->mutex); 91 92 drm_modeset_acquire_init(ctx, 0); 93 94 retry: 95 ret = drm_modeset_lock_all_ctx(dev, ctx); 96 if (ret < 0) { 97 if (ret == -EDEADLK) { 98 drm_modeset_backoff(ctx); 99 goto retry; 100 } 101 102 drm_modeset_acquire_fini(ctx); 103 kfree(ctx); 104 return; 105 } 106 107 WARN_ON(config->acquire_ctx); 108 109 /* 110 * We hold the locks now, so it is safe to stash the acquisition 111 * context for drm_modeset_unlock_all(). 112 */ 113 config->acquire_ctx = ctx; 114 115 drm_warn_on_modeset_not_all_locked(dev); 116 } 117 EXPORT_SYMBOL(drm_modeset_lock_all); 118 119 /** 120 * drm_modeset_unlock_all - drop all modeset locks 121 * @dev: DRM device 122 * 123 * This function drops all modeset locks taken by a previous call to the 124 * drm_modeset_lock_all() function. 125 * 126 * This function is deprecated. It uses the lock acquisition context stored 127 * in &drm_device.mode_config. This facilitates conversion of existing 128 * code because it removes the need to manually deal with the acquisition 129 * context, but it is also brittle because the context is global and care must 130 * be taken not to nest calls. New code should pass the acquisition context 131 * directly to the drm_modeset_drop_locks() function. 132 */ 133 void drm_modeset_unlock_all(struct drm_device *dev) 134 { 135 struct drm_mode_config *config = &dev->mode_config; 136 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 137 138 if (WARN_ON(!ctx)) 139 return; 140 141 config->acquire_ctx = NULL; 142 drm_modeset_drop_locks(ctx); 143 drm_modeset_acquire_fini(ctx); 144 145 kfree(ctx); 146 147 mutex_unlock(&dev->mode_config.mutex); 148 } 149 EXPORT_SYMBOL(drm_modeset_unlock_all); 150 151 /** 152 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update 153 * @crtc: DRM CRTC 154 * @plane: DRM plane to be updated on @crtc 155 * 156 * This function locks the given crtc and plane (which should be either the 157 * primary or cursor plane) using a hidden acquire context. This is necessary so 158 * that drivers internally using the atomic interfaces can grab further locks 159 * with the lock acquire context. 160 * 161 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been 162 * converted to universal planes yet. 163 */ 164 void drm_modeset_lock_crtc(struct drm_crtc *crtc, 165 struct drm_plane *plane) 166 { 167 struct drm_modeset_acquire_ctx *ctx; 168 int ret; 169 170 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 171 if (WARN_ON(!ctx)) 172 return; 173 174 drm_modeset_acquire_init(ctx, 0); 175 176 retry: 177 ret = drm_modeset_lock(&crtc->mutex, ctx); 178 if (ret) 179 goto fail; 180 181 if (plane) { 182 ret = drm_modeset_lock(&plane->mutex, ctx); 183 if (ret) 184 goto fail; 185 186 if (plane->crtc) { 187 ret = drm_modeset_lock(&plane->crtc->mutex, ctx); 188 if (ret) 189 goto fail; 190 } 191 } 192 193 WARN_ON(crtc->acquire_ctx); 194 195 /* now we hold the locks, so now that it is safe, stash the 196 * ctx for drm_modeset_unlock_crtc(): 197 */ 198 crtc->acquire_ctx = ctx; 199 200 return; 201 202 fail: 203 if (ret == -EDEADLK) { 204 drm_modeset_backoff(ctx); 205 goto retry; 206 } 207 } 208 EXPORT_SYMBOL(drm_modeset_lock_crtc); 209 210 /** 211 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls 212 * @crtc: drm crtc 213 * 214 * Legacy ioctl operations like cursor updates or page flips only have per-crtc 215 * locking, and store the acquire ctx in the corresponding crtc. All other 216 * legacy operations take all locks and use a global acquire context. This 217 * function grabs the right one. 218 */ 219 struct drm_modeset_acquire_ctx * 220 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc) 221 { 222 if (crtc->acquire_ctx) 223 return crtc->acquire_ctx; 224 225 WARN_ON(!crtc->dev->mode_config.acquire_ctx); 226 227 return crtc->dev->mode_config.acquire_ctx; 228 } 229 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx); 230 231 /** 232 * drm_modeset_unlock_crtc - drop crtc lock 233 * @crtc: drm crtc 234 * 235 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other 236 * locks acquired through the hidden context. 237 */ 238 void drm_modeset_unlock_crtc(struct drm_crtc *crtc) 239 { 240 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx; 241 242 if (WARN_ON(!ctx)) 243 return; 244 245 crtc->acquire_ctx = NULL; 246 drm_modeset_drop_locks(ctx); 247 drm_modeset_acquire_fini(ctx); 248 249 kfree(ctx); 250 } 251 EXPORT_SYMBOL(drm_modeset_unlock_crtc); 252 253 /** 254 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 255 * @dev: device 256 * 257 * Useful as a debug assert. 258 */ 259 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 260 { 261 struct drm_crtc *crtc; 262 263 /* Locking is currently fubar in the panic handler. */ 264 if (oops_in_progress) 265 return; 266 267 drm_for_each_crtc(crtc, dev) 268 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 269 270 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 271 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 272 } 273 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 274 275 /** 276 * drm_modeset_acquire_init - initialize acquire context 277 * @ctx: the acquire context 278 * @flags: for future 279 */ 280 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 281 uint32_t flags) 282 { 283 memset(ctx, 0, sizeof(*ctx)); 284 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 285 INIT_LIST_HEAD(&ctx->locked); 286 } 287 EXPORT_SYMBOL(drm_modeset_acquire_init); 288 289 /** 290 * drm_modeset_acquire_fini - cleanup acquire context 291 * @ctx: the acquire context 292 */ 293 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 294 { 295 ww_acquire_fini(&ctx->ww_ctx); 296 } 297 EXPORT_SYMBOL(drm_modeset_acquire_fini); 298 299 /** 300 * drm_modeset_drop_locks - drop all locks 301 * @ctx: the acquire context 302 * 303 * Drop all locks currently held against this acquire context. 304 */ 305 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 306 { 307 WARN_ON(ctx->contended); 308 while (!list_empty(&ctx->locked)) { 309 struct drm_modeset_lock *lock; 310 311 lock = list_first_entry(&ctx->locked, 312 struct drm_modeset_lock, head); 313 314 drm_modeset_unlock(lock); 315 } 316 } 317 EXPORT_SYMBOL(drm_modeset_drop_locks); 318 319 static inline int modeset_lock(struct drm_modeset_lock *lock, 320 struct drm_modeset_acquire_ctx *ctx, 321 bool interruptible, bool slow) 322 { 323 int ret; 324 325 WARN_ON(ctx->contended); 326 327 if (ctx->trylock_only) { 328 lockdep_assert_held(&ctx->ww_ctx); 329 330 if (!ww_mutex_trylock(&lock->mutex)) 331 return -EBUSY; 332 else 333 return 0; 334 } else if (interruptible && slow) { 335 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 336 } else if (interruptible) { 337 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 338 } else if (slow) { 339 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 340 ret = 0; 341 } else { 342 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 343 } 344 if (!ret) { 345 WARN_ON(!list_empty(&lock->head)); 346 list_add(&lock->head, &ctx->locked); 347 } else if (ret == -EALREADY) { 348 /* we already hold the lock.. this is fine. For atomic 349 * we will need to be able to drm_modeset_lock() things 350 * without having to keep track of what is already locked 351 * or not. 352 */ 353 ret = 0; 354 } else if (ret == -EDEADLK) { 355 ctx->contended = lock; 356 } 357 358 return ret; 359 } 360 361 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, 362 bool interruptible) 363 { 364 struct drm_modeset_lock *contended = ctx->contended; 365 366 ctx->contended = NULL; 367 368 if (WARN_ON(!contended)) 369 return 0; 370 371 drm_modeset_drop_locks(ctx); 372 373 return modeset_lock(contended, ctx, interruptible, true); 374 } 375 376 /** 377 * drm_modeset_backoff - deadlock avoidance backoff 378 * @ctx: the acquire context 379 * 380 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 381 * you must call this function to drop all currently held locks and 382 * block until the contended lock becomes available. 383 */ 384 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 385 { 386 modeset_backoff(ctx, false); 387 } 388 EXPORT_SYMBOL(drm_modeset_backoff); 389 390 /** 391 * drm_modeset_backoff_interruptible - deadlock avoidance backoff 392 * @ctx: the acquire context 393 * 394 * Interruptible version of drm_modeset_backoff() 395 */ 396 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) 397 { 398 return modeset_backoff(ctx, true); 399 } 400 EXPORT_SYMBOL(drm_modeset_backoff_interruptible); 401 402 /** 403 * drm_modeset_lock_init - initialize lock 404 * @lock: lock to init 405 */ 406 void drm_modeset_lock_init(struct drm_modeset_lock *lock) 407 { 408 ww_mutex_init(&lock->mutex, &crtc_ww_class); 409 INIT_LIST_HEAD(&lock->head); 410 } 411 EXPORT_SYMBOL(drm_modeset_lock_init); 412 413 /** 414 * drm_modeset_lock - take modeset lock 415 * @lock: lock to take 416 * @ctx: acquire ctx 417 * 418 * If ctx is not NULL, then its ww acquire context is used and the 419 * lock will be tracked by the context and can be released by calling 420 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 421 * deadlock scenario has been detected and it is an error to attempt 422 * to take any more locks without first calling drm_modeset_backoff(). 423 */ 424 int drm_modeset_lock(struct drm_modeset_lock *lock, 425 struct drm_modeset_acquire_ctx *ctx) 426 { 427 if (ctx) 428 return modeset_lock(lock, ctx, false, false); 429 430 ww_mutex_lock(&lock->mutex, NULL); 431 return 0; 432 } 433 EXPORT_SYMBOL(drm_modeset_lock); 434 435 /** 436 * drm_modeset_lock_interruptible - take modeset lock 437 * @lock: lock to take 438 * @ctx: acquire ctx 439 * 440 * Interruptible version of drm_modeset_lock() 441 */ 442 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, 443 struct drm_modeset_acquire_ctx *ctx) 444 { 445 if (ctx) 446 return modeset_lock(lock, ctx, true, false); 447 448 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 449 } 450 EXPORT_SYMBOL(drm_modeset_lock_interruptible); 451 452 /** 453 * drm_modeset_unlock - drop modeset lock 454 * @lock: lock to release 455 */ 456 void drm_modeset_unlock(struct drm_modeset_lock *lock) 457 { 458 list_del_init(&lock->head); 459 ww_mutex_unlock(&lock->mutex); 460 } 461 EXPORT_SYMBOL(drm_modeset_unlock); 462 463 /** 464 * drm_modeset_lock_all_ctx - take all modeset locks 465 * @dev: DRM device 466 * @ctx: lock acquisition context 467 * 468 * This function takes all modeset locks, suitable where a more fine-grained 469 * scheme isn't (yet) implemented. 470 * 471 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 472 * since that lock isn't required for modeset state changes. Callers which 473 * need to grab that lock too need to do so outside of the acquire context 474 * @ctx. 475 * 476 * Locks acquired with this function should be released by calling the 477 * drm_modeset_drop_locks() function on @ctx. 478 * 479 * Returns: 0 on success or a negative error-code on failure. 480 */ 481 int drm_modeset_lock_all_ctx(struct drm_device *dev, 482 struct drm_modeset_acquire_ctx *ctx) 483 { 484 struct drm_crtc *crtc; 485 struct drm_plane *plane; 486 int ret; 487 488 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 489 if (ret) 490 return ret; 491 492 drm_for_each_crtc(crtc, dev) { 493 ret = drm_modeset_lock(&crtc->mutex, ctx); 494 if (ret) 495 return ret; 496 } 497 498 drm_for_each_plane(plane, dev) { 499 ret = drm_modeset_lock(&plane->mutex, ctx); 500 if (ret) 501 return ret; 502 } 503 504 return 0; 505 } 506 EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 507