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_warn_on_modeset_not_all_locked - check that all modeset locks are locked 153 * @dev: device 154 * 155 * Useful as a debug assert. 156 */ 157 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 158 { 159 struct drm_crtc *crtc; 160 161 /* Locking is currently fubar in the panic handler. */ 162 #ifdef __DragonFly__ 163 if (panicstr) 164 return; 165 #else 166 if (oops_in_progress) 167 return; 168 #endif 169 170 drm_for_each_crtc(crtc, dev) 171 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 172 173 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 174 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 175 } 176 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 177 178 /** 179 * drm_modeset_acquire_init - initialize acquire context 180 * @ctx: the acquire context 181 * @flags: for future 182 */ 183 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 184 uint32_t flags) 185 { 186 memset(ctx, 0, sizeof(*ctx)); 187 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 188 INIT_LIST_HEAD(&ctx->locked); 189 } 190 EXPORT_SYMBOL(drm_modeset_acquire_init); 191 192 /** 193 * drm_modeset_acquire_fini - cleanup acquire context 194 * @ctx: the acquire context 195 */ 196 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 197 { 198 ww_acquire_fini(&ctx->ww_ctx); 199 } 200 EXPORT_SYMBOL(drm_modeset_acquire_fini); 201 202 /** 203 * drm_modeset_drop_locks - drop all locks 204 * @ctx: the acquire context 205 * 206 * Drop all locks currently held against this acquire context. 207 */ 208 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 209 { 210 WARN_ON(ctx->contended); 211 while (!list_empty(&ctx->locked)) { 212 struct drm_modeset_lock_info *info; 213 214 info = list_first_entry(&ctx->locked, 215 struct drm_modeset_lock_info, ctx_entry); 216 217 drm_modeset_unlock(info->lock); 218 } 219 } 220 EXPORT_SYMBOL(drm_modeset_drop_locks); 221 222 static inline int modeset_lock(struct drm_modeset_lock *lock, 223 struct drm_modeset_acquire_ctx *ctx, 224 bool interruptible, bool slow) 225 { 226 int ret; 227 228 WARN_ON(ctx->contended); 229 230 if (ctx->trylock_only) { 231 #if 0 232 lockdep_assert_held(&ctx->ww_ctx); 233 #endif 234 235 if (!ww_mutex_trylock(&lock->mutex)) 236 return -EBUSY; 237 else 238 return 0; 239 } else if (interruptible && slow) { 240 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 241 } else if (interruptible) { 242 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 243 } else if (slow) { 244 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 245 ret = 0; 246 } else { 247 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 248 } 249 if (ret == -EALREADY) { 250 /* we already hold the lock.. this is fine. For atomic 251 * we will need to be able to drm_modeset_lock() things 252 * without having to keep track of what is already locked 253 * or not. 254 */ 255 ret = 0; 256 } else if (ret == -EDEADLK) { 257 ctx->contended = lock; 258 } 259 if (ret == 0) { 260 struct drm_modeset_lock_info *info; 261 262 info = kzalloc(sizeof(*info), GFP_KERNEL); 263 INIT_LIST_HEAD(&info->ctx_entry); 264 INIT_LIST_HEAD(&info->lock_entry); 265 info->lock = lock; 266 info->ctx = ctx; 267 list_add(&info->ctx_entry, &ctx->locked); 268 list_add(&info->lock_entry, &lock->head); 269 } 270 271 return ret; 272 } 273 274 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, 275 bool interruptible) 276 { 277 struct drm_modeset_lock *contended = ctx->contended; 278 279 ctx->contended = NULL; 280 281 if (WARN_ON(!contended)) 282 return 0; 283 284 drm_modeset_drop_locks(ctx); 285 286 return modeset_lock(contended, ctx, interruptible, true); 287 } 288 289 /** 290 * drm_modeset_backoff - deadlock avoidance backoff 291 * @ctx: the acquire context 292 * 293 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 294 * you must call this function to drop all currently held locks and 295 * block until the contended lock becomes available. 296 */ 297 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 298 { 299 modeset_backoff(ctx, false); 300 } 301 EXPORT_SYMBOL(drm_modeset_backoff); 302 303 /** 304 * drm_modeset_backoff_interruptible - deadlock avoidance backoff 305 * @ctx: the acquire context 306 * 307 * Interruptible version of drm_modeset_backoff() 308 */ 309 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) 310 { 311 return modeset_backoff(ctx, true); 312 } 313 EXPORT_SYMBOL(drm_modeset_backoff_interruptible); 314 315 /** 316 * drm_modeset_lock_init - initialize lock 317 * @lock: lock to init 318 */ 319 void drm_modeset_lock_init(struct drm_modeset_lock *lock) 320 { 321 ww_mutex_init(&lock->mutex, &crtc_ww_class); 322 INIT_LIST_HEAD(&lock->head); 323 } 324 EXPORT_SYMBOL(drm_modeset_lock_init); 325 326 /** 327 * drm_modeset_lock - take modeset lock 328 * @lock: lock to take 329 * @ctx: acquire ctx 330 * 331 * If ctx is not NULL, then its ww acquire context is used and the 332 * lock will be tracked by the context and can be released by calling 333 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 334 * deadlock scenario has been detected and it is an error to attempt 335 * to take any more locks without first calling drm_modeset_backoff(). 336 */ 337 int drm_modeset_lock(struct drm_modeset_lock *lock, 338 struct drm_modeset_acquire_ctx *ctx) 339 { 340 if (ctx) 341 return modeset_lock(lock, ctx, false, false); 342 343 ww_mutex_lock(&lock->mutex, NULL); 344 return 0; 345 } 346 EXPORT_SYMBOL(drm_modeset_lock); 347 348 /** 349 * drm_modeset_lock_interruptible - take modeset lock 350 * @lock: lock to take 351 * @ctx: acquire ctx 352 * 353 * Interruptible version of drm_modeset_lock() 354 */ 355 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, 356 struct drm_modeset_acquire_ctx *ctx) 357 { 358 if (ctx) 359 return modeset_lock(lock, ctx, true, false); 360 361 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 362 } 363 EXPORT_SYMBOL(drm_modeset_lock_interruptible); 364 365 /** 366 * drm_modeset_unlock - drop modeset lock 367 * @lock: lock to release 368 */ 369 void drm_modeset_unlock(struct drm_modeset_lock *lock) 370 { 371 struct drm_modeset_lock_info *info; 372 373 /* undo in reverse order */ 374 if (!list_empty(&lock->head)) { 375 info = list_last_entry(&lock->head, 376 struct drm_modeset_lock_info, lock_entry); 377 list_del_init(&info->lock_entry); 378 if (info->ctx) 379 list_del_init(&info->ctx_entry); 380 kfree(info); 381 } 382 ww_mutex_unlock(&lock->mutex); 383 } 384 EXPORT_SYMBOL(drm_modeset_unlock); 385 386 /** 387 * drm_modeset_lock_all_ctx - take all modeset locks 388 * @dev: DRM device 389 * @ctx: lock acquisition context 390 * 391 * This function takes all modeset locks, suitable where a more fine-grained 392 * scheme isn't (yet) implemented. 393 * 394 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 395 * since that lock isn't required for modeset state changes. Callers which 396 * need to grab that lock too need to do so outside of the acquire context 397 * @ctx. 398 * 399 * Locks acquired with this function should be released by calling the 400 * drm_modeset_drop_locks() function on @ctx. 401 * 402 * Returns: 0 on success or a negative error-code on failure. 403 */ 404 int drm_modeset_lock_all_ctx(struct drm_device *dev, 405 struct drm_modeset_acquire_ctx *ctx) 406 { 407 struct drm_crtc *crtc; 408 struct drm_plane *plane; 409 int ret; 410 411 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 412 if (ret) 413 return ret; 414 415 drm_for_each_crtc(crtc, dev) { 416 ret = drm_modeset_lock(&crtc->mutex, ctx); 417 if (ret) 418 return ret; 419 } 420 421 drm_for_each_plane(plane, dev) { 422 ret = drm_modeset_lock(&plane->mutex, ctx); 423 if (ret) 424 return ret; 425 } 426 427 return 0; 428 } 429 EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 430