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