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, DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 43 * retry: 44 * foreach (lock in random_ordered_set_of_locks) { 45 * ret = drm_modeset_lock(lock, ctx) 46 * if (ret == -EDEADLK) { 47 * ret = drm_modeset_backoff(ctx); 48 * if (!ret) 49 * goto retry; 50 * } 51 * if (ret) 52 * goto out; 53 * } 54 * ... do stuff ... 55 * out: 56 * drm_modeset_drop_locks(ctx); 57 * drm_modeset_acquire_fini(ctx); 58 * 59 * If all that is needed is a single modeset lock, then the &struct 60 * drm_modeset_acquire_ctx is not needed and the locking can be simplified 61 * by passing a NULL instead of ctx in the drm_modeset_lock() call or 62 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards 63 * call drm_modeset_unlock(). 64 * 65 * On top of these per-object locks using &ww_mutex there's also an overall 66 * &drm_mode_config.mutex, for protecting everything else. Mostly this means 67 * probe state of connectors, and preventing hotplug add/removal of connectors. 68 * 69 * Finally there's a bunch of dedicated locks to protect drm core internal 70 * lists and lookup data structures. 71 */ 72 73 static DEFINE_WW_CLASS(crtc_ww_class); 74 75 /** 76 * drm_modeset_lock_all - take all modeset locks 77 * @dev: DRM device 78 * 79 * This function takes all modeset locks, suitable where a more fine-grained 80 * scheme isn't (yet) implemented. Locks must be dropped by calling the 81 * drm_modeset_unlock_all() function. 82 * 83 * This function is deprecated. It allocates a lock acquisition context and 84 * stores it in &drm_device.mode_config. This facilitate conversion of 85 * existing code because it removes the need to manually deal with the 86 * acquisition context, but it is also brittle because the context is global 87 * and care must be taken not to nest calls. New code should use the 88 * drm_modeset_lock_all_ctx() function and pass in the context explicitly. 89 */ 90 void drm_modeset_lock_all(struct drm_device *dev) 91 { 92 struct drm_mode_config *config = &dev->mode_config; 93 struct drm_modeset_acquire_ctx *ctx; 94 int ret; 95 96 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL); 97 if (WARN_ON(!ctx)) 98 return; 99 100 mutex_lock(&config->mutex); 101 102 drm_modeset_acquire_init(ctx, 0); 103 104 retry: 105 ret = drm_modeset_lock_all_ctx(dev, ctx); 106 if (ret < 0) { 107 if (ret == -EDEADLK) { 108 drm_modeset_backoff(ctx); 109 goto retry; 110 } 111 112 drm_modeset_acquire_fini(ctx); 113 kfree(ctx); 114 return; 115 } 116 117 WARN_ON(config->acquire_ctx); 118 119 /* 120 * We hold the locks now, so it is safe to stash the acquisition 121 * context for drm_modeset_unlock_all(). 122 */ 123 config->acquire_ctx = ctx; 124 125 drm_warn_on_modeset_not_all_locked(dev); 126 } 127 EXPORT_SYMBOL(drm_modeset_lock_all); 128 129 /** 130 * drm_modeset_unlock_all - drop all modeset locks 131 * @dev: DRM device 132 * 133 * This function drops all modeset locks taken by a previous call to the 134 * drm_modeset_lock_all() function. 135 * 136 * This function is deprecated. It uses the lock acquisition context stored 137 * in &drm_device.mode_config. This facilitates conversion of existing 138 * code because it removes the need to manually deal with the acquisition 139 * context, but it is also brittle because the context is global and care must 140 * be taken not to nest calls. New code should pass the acquisition context 141 * directly to the drm_modeset_drop_locks() function. 142 */ 143 void drm_modeset_unlock_all(struct drm_device *dev) 144 { 145 struct drm_mode_config *config = &dev->mode_config; 146 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 147 148 if (WARN_ON(!ctx)) 149 return; 150 151 config->acquire_ctx = NULL; 152 drm_modeset_drop_locks(ctx); 153 drm_modeset_acquire_fini(ctx); 154 155 kfree(ctx); 156 157 mutex_unlock(&dev->mode_config.mutex); 158 } 159 EXPORT_SYMBOL(drm_modeset_unlock_all); 160 161 /** 162 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 163 * @dev: device 164 * 165 * Useful as a debug assert. 166 */ 167 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 168 { 169 struct drm_crtc *crtc; 170 171 /* Locking is currently fubar in the panic handler. */ 172 #ifdef __DragonFly__ 173 if (panicstr) 174 return; 175 #else 176 if (oops_in_progress) 177 return; 178 #endif 179 180 drm_for_each_crtc(crtc, dev) 181 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 182 183 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 184 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 185 } 186 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 187 188 /** 189 * drm_modeset_acquire_init - initialize acquire context 190 * @ctx: the acquire context 191 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE 192 * 193 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags, 194 * all calls to drm_modeset_lock() will perform an interruptible 195 * wait. 196 */ 197 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 198 uint32_t flags) 199 { 200 memset(ctx, 0, sizeof(*ctx)); 201 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 202 INIT_LIST_HEAD(&ctx->locked); 203 204 if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 205 ctx->interruptible = true; 206 } 207 EXPORT_SYMBOL(drm_modeset_acquire_init); 208 209 /** 210 * drm_modeset_acquire_fini - cleanup acquire context 211 * @ctx: the acquire context 212 */ 213 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 214 { 215 ww_acquire_fini(&ctx->ww_ctx); 216 } 217 EXPORT_SYMBOL(drm_modeset_acquire_fini); 218 219 /** 220 * drm_modeset_drop_locks - drop all locks 221 * @ctx: the acquire context 222 * 223 * Drop all locks currently held against this acquire context. 224 */ 225 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 226 { 227 WARN_ON(ctx->contended); 228 while (!list_empty(&ctx->locked)) { 229 struct drm_modeset_lock_info *info; 230 231 info = list_first_entry(&ctx->locked, 232 struct drm_modeset_lock_info, ctx_entry); 233 234 drm_modeset_unlock(info->lock); 235 } 236 } 237 EXPORT_SYMBOL(drm_modeset_drop_locks); 238 239 static inline int modeset_lock(struct drm_modeset_lock *lock, 240 struct drm_modeset_acquire_ctx *ctx, 241 bool interruptible, bool slow) 242 { 243 int ret; 244 245 WARN_ON(ctx->contended); 246 247 if (ctx->trylock_only) { 248 #if 0 249 lockdep_assert_held(&ctx->ww_ctx); 250 #endif 251 252 if (!ww_mutex_trylock(&lock->mutex)) 253 return -EBUSY; 254 else 255 return 0; 256 } else if (interruptible && slow) { 257 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 258 } else if (interruptible) { 259 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 260 } else if (slow) { 261 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 262 ret = 0; 263 } else { 264 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 265 } 266 if (ret == -EALREADY) { 267 /* we already hold the lock.. this is fine. For atomic 268 * we will need to be able to drm_modeset_lock() things 269 * without having to keep track of what is already locked 270 * or not. 271 */ 272 ret = 0; 273 } else if (ret == -EDEADLK) { 274 ctx->contended = lock; 275 } 276 if (ret == 0) { 277 struct drm_modeset_lock_info *info; 278 279 info = kzalloc(sizeof(*info), GFP_KERNEL); 280 INIT_LIST_HEAD(&info->ctx_entry); 281 INIT_LIST_HEAD(&info->lock_entry); 282 info->lock = lock; 283 info->ctx = ctx; 284 list_add(&info->ctx_entry, &ctx->locked); 285 list_add(&info->lock_entry, &lock->head); 286 } 287 288 return ret; 289 } 290 291 /** 292 * drm_modeset_backoff - deadlock avoidance backoff 293 * @ctx: the acquire context 294 * 295 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 296 * you must call this function to drop all currently held locks and 297 * block until the contended lock becomes available. 298 * 299 * This function returns 0 on success, or -ERESTARTSYS if this context 300 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the 301 * wait has been interrupted. 302 */ 303 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 304 { 305 struct drm_modeset_lock *contended = ctx->contended; 306 307 ctx->contended = NULL; 308 309 if (WARN_ON(!contended)) 310 return 0; 311 312 drm_modeset_drop_locks(ctx); 313 314 return modeset_lock(contended, ctx, ctx->interruptible, true); 315 } 316 EXPORT_SYMBOL(drm_modeset_backoff); 317 318 /** 319 * drm_modeset_lock_init - initialize lock 320 * @lock: lock to init 321 */ 322 void drm_modeset_lock_init(struct drm_modeset_lock *lock) 323 { 324 ww_mutex_init(&lock->mutex, &crtc_ww_class); 325 INIT_LIST_HEAD(&lock->head); 326 } 327 EXPORT_SYMBOL(drm_modeset_lock_init); 328 329 /** 330 * drm_modeset_lock - take modeset lock 331 * @lock: lock to take 332 * @ctx: acquire ctx 333 * 334 * If @ctx is not NULL, then its ww acquire context is used and the 335 * lock will be tracked by the context and can be released by calling 336 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 337 * deadlock scenario has been detected and it is an error to attempt 338 * to take any more locks without first calling drm_modeset_backoff(). 339 * 340 * If the @ctx is not NULL and initialized with 341 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with 342 * -ERESTARTSYS when interrupted. 343 * 344 * If @ctx is NULL then the function call behaves like a normal, 345 * uninterruptible non-nesting mutex_lock() call. 346 */ 347 int drm_modeset_lock(struct drm_modeset_lock *lock, 348 struct drm_modeset_acquire_ctx *ctx) 349 { 350 if (ctx) 351 return modeset_lock(lock, ctx, ctx->interruptible, false); 352 353 ww_mutex_lock(&lock->mutex, NULL); 354 return 0; 355 } 356 EXPORT_SYMBOL(drm_modeset_lock); 357 358 /** 359 * drm_modeset_lock_single_interruptible - take a single modeset lock 360 * @lock: lock to take 361 * 362 * This function behaves as drm_modeset_lock() with a NULL context, 363 * but performs interruptible waits. 364 * 365 * This function returns 0 on success, or -ERESTARTSYS when interrupted. 366 */ 367 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock) 368 { 369 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 370 } 371 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible); 372 373 /** 374 * drm_modeset_unlock - drop modeset lock 375 * @lock: lock to release 376 */ 377 void drm_modeset_unlock(struct drm_modeset_lock *lock) 378 { 379 struct drm_modeset_lock_info *info; 380 381 /* undo in reverse order */ 382 if (!list_empty(&lock->head)) { 383 info = list_last_entry(&lock->head, 384 struct drm_modeset_lock_info, lock_entry); 385 list_del_init(&info->lock_entry); 386 if (info->ctx) 387 list_del_init(&info->ctx_entry); 388 kfree(info); 389 } 390 ww_mutex_unlock(&lock->mutex); 391 } 392 EXPORT_SYMBOL(drm_modeset_unlock); 393 394 /** 395 * drm_modeset_lock_all_ctx - take all modeset locks 396 * @dev: DRM device 397 * @ctx: lock acquisition context 398 * 399 * This function takes all modeset locks, suitable where a more fine-grained 400 * scheme isn't (yet) implemented. 401 * 402 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 403 * since that lock isn't required for modeset state changes. Callers which 404 * need to grab that lock too need to do so outside of the acquire context 405 * @ctx. 406 * 407 * Locks acquired with this function should be released by calling the 408 * drm_modeset_drop_locks() function on @ctx. 409 * 410 * Returns: 0 on success or a negative error-code on failure. 411 */ 412 int drm_modeset_lock_all_ctx(struct drm_device *dev, 413 struct drm_modeset_acquire_ctx *ctx) 414 { 415 struct drm_crtc *crtc; 416 struct drm_plane *plane; 417 int ret; 418 419 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 420 if (ret) 421 return ret; 422 423 drm_for_each_crtc(crtc, dev) { 424 ret = drm_modeset_lock(&crtc->mutex, ctx); 425 if (ret) 426 return ret; 427 } 428 429 drm_for_each_plane(plane, dev) { 430 ret = drm_modeset_lock(&plane->mutex, ctx); 431 if (ret) 432 return ret; 433 } 434 435 return 0; 436 } 437 EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 438