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