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/drm_atomic.h> 25 #include <drm/drm_crtc.h> 26 #include <drm/drm_device.h> 27 #include <drm/drm_modeset_lock.h> 28 29 /** 30 * DOC: kms locking 31 * 32 * As KMS moves toward more fine grained locking, and atomic ioctl where 33 * userspace can indirectly control locking order, it becomes necessary 34 * to use &ww_mutex and acquire-contexts to avoid deadlocks. But because 35 * the locking is more distributed around the driver code, we want a bit 36 * of extra utility/tracking out of our acquire-ctx. This is provided 37 * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx. 38 * 39 * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.rst 40 * 41 * The basic usage pattern is to:: 42 * 43 * drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 44 * retry: 45 * foreach (lock in random_ordered_set_of_locks) { 46 * ret = drm_modeset_lock(lock, ctx) 47 * if (ret == -EDEADLK) { 48 * ret = drm_modeset_backoff(ctx); 49 * if (!ret) 50 * goto retry; 51 * } 52 * if (ret) 53 * goto out; 54 * } 55 * ... do stuff ... 56 * out: 57 * drm_modeset_drop_locks(ctx); 58 * drm_modeset_acquire_fini(ctx); 59 * 60 * For convenience this control flow is implemented in 61 * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case 62 * where all modeset locks need to be taken through drm_modeset_lock_all_ctx(). 63 * 64 * If all that is needed is a single modeset lock, then the &struct 65 * drm_modeset_acquire_ctx is not needed and the locking can be simplified 66 * by passing a NULL instead of ctx in the drm_modeset_lock() call or 67 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards 68 * call drm_modeset_unlock(). 69 * 70 * On top of these per-object locks using &ww_mutex there's also an overall 71 * &drm_mode_config.mutex, for protecting everything else. Mostly this means 72 * probe state of connectors, and preventing hotplug add/removal of connectors. 73 * 74 * Finally there's a bunch of dedicated locks to protect drm core internal 75 * lists and lookup data structures. 76 */ 77 78 static DEFINE_WW_CLASS(crtc_ww_class); 79 80 /** 81 * drm_modeset_lock_all - take all modeset locks 82 * @dev: DRM device 83 * 84 * This function takes all modeset locks, suitable where a more fine-grained 85 * scheme isn't (yet) implemented. Locks must be dropped by calling the 86 * drm_modeset_unlock_all() function. 87 * 88 * This function is deprecated. It allocates a lock acquisition context and 89 * stores it in &drm_device.mode_config. This facilitate conversion of 90 * existing code because it removes the need to manually deal with the 91 * acquisition context, but it is also brittle because the context is global 92 * and care must be taken not to nest calls. New code should use the 93 * drm_modeset_lock_all_ctx() function and pass in the context explicitly. 94 */ 95 void drm_modeset_lock_all(struct drm_device *dev) 96 { 97 struct drm_mode_config *config = &dev->mode_config; 98 struct drm_modeset_acquire_ctx *ctx; 99 int ret; 100 101 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL); 102 if (WARN_ON(!ctx)) 103 return; 104 105 mutex_lock(&config->mutex); 106 107 drm_modeset_acquire_init(ctx, 0); 108 109 retry: 110 ret = drm_modeset_lock_all_ctx(dev, ctx); 111 if (ret < 0) { 112 if (ret == -EDEADLK) { 113 drm_modeset_backoff(ctx); 114 goto retry; 115 } 116 117 drm_modeset_acquire_fini(ctx); 118 kfree(ctx); 119 return; 120 } 121 ww_acquire_done(&ctx->ww_ctx); 122 123 WARN_ON(config->acquire_ctx); 124 125 /* 126 * We hold the locks now, so it is safe to stash the acquisition 127 * context for drm_modeset_unlock_all(). 128 */ 129 config->acquire_ctx = ctx; 130 131 drm_warn_on_modeset_not_all_locked(dev); 132 } 133 EXPORT_SYMBOL(drm_modeset_lock_all); 134 135 /** 136 * drm_modeset_unlock_all - drop all modeset locks 137 * @dev: DRM device 138 * 139 * This function drops all modeset locks taken by a previous call to the 140 * drm_modeset_lock_all() function. 141 * 142 * This function is deprecated. It uses the lock acquisition context stored 143 * in &drm_device.mode_config. This facilitates conversion of existing 144 * code because it removes the need to manually deal with the acquisition 145 * context, but it is also brittle because the context is global and care must 146 * be taken not to nest calls. New code should pass the acquisition context 147 * directly to the drm_modeset_drop_locks() function. 148 */ 149 void drm_modeset_unlock_all(struct drm_device *dev) 150 { 151 struct drm_mode_config *config = &dev->mode_config; 152 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 153 154 if (WARN_ON(!ctx)) 155 return; 156 157 config->acquire_ctx = NULL; 158 drm_modeset_drop_locks(ctx); 159 drm_modeset_acquire_fini(ctx); 160 161 kfree(ctx); 162 163 mutex_unlock(&dev->mode_config.mutex); 164 } 165 EXPORT_SYMBOL(drm_modeset_unlock_all); 166 167 /** 168 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 169 * @dev: device 170 * 171 * Useful as a debug assert. 172 */ 173 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 174 { 175 struct drm_crtc *crtc; 176 177 /* Locking is currently fubar in the panic handler. */ 178 if (oops_in_progress) 179 return; 180 181 drm_for_each_crtc(crtc, dev) 182 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 183 184 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 185 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 186 } 187 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 188 189 /** 190 * drm_modeset_acquire_init - initialize acquire context 191 * @ctx: the acquire context 192 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE 193 * 194 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags, 195 * all calls to drm_modeset_lock() will perform an interruptible 196 * wait. 197 */ 198 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 199 uint32_t flags) 200 { 201 memset(ctx, 0, sizeof(*ctx)); 202 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 203 INIT_LIST_HEAD(&ctx->locked); 204 205 if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 206 ctx->interruptible = true; 207 } 208 EXPORT_SYMBOL(drm_modeset_acquire_init); 209 210 /** 211 * drm_modeset_acquire_fini - cleanup acquire context 212 * @ctx: the acquire context 213 */ 214 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 215 { 216 ww_acquire_fini(&ctx->ww_ctx); 217 } 218 EXPORT_SYMBOL(drm_modeset_acquire_fini); 219 220 /** 221 * drm_modeset_drop_locks - drop all locks 222 * @ctx: the acquire context 223 * 224 * Drop all locks currently held against this acquire context. 225 */ 226 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 227 { 228 WARN_ON(ctx->contended); 229 while (!list_empty(&ctx->locked)) { 230 struct drm_modeset_lock *lock; 231 232 lock = list_first_entry(&ctx->locked, 233 struct drm_modeset_lock, head); 234 235 drm_modeset_unlock(lock); 236 } 237 } 238 EXPORT_SYMBOL(drm_modeset_drop_locks); 239 240 static inline int modeset_lock(struct drm_modeset_lock *lock, 241 struct drm_modeset_acquire_ctx *ctx, 242 bool interruptible, bool slow) 243 { 244 int ret; 245 246 WARN_ON(ctx->contended); 247 248 if (ctx->trylock_only) { 249 lockdep_assert_held(&ctx->ww_ctx); 250 251 if (!ww_mutex_trylock(&lock->mutex)) 252 return -EBUSY; 253 else 254 return 0; 255 } else if (interruptible && slow) { 256 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 257 } else if (interruptible) { 258 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 259 } else if (slow) { 260 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 261 ret = 0; 262 } else { 263 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 264 } 265 if (!ret) { 266 WARN_ON(!list_empty(&lock->head)); 267 list_add(&lock->head, &ctx->locked); 268 } else if (ret == -EALREADY) { 269 /* we already hold the lock.. this is fine. For atomic 270 * we will need to be able to drm_modeset_lock() things 271 * without having to keep track of what is already locked 272 * or not. 273 */ 274 ret = 0; 275 } else if (ret == -EDEADLK) { 276 ctx->contended = lock; 277 } 278 279 return ret; 280 } 281 282 /** 283 * drm_modeset_backoff - deadlock avoidance backoff 284 * @ctx: the acquire context 285 * 286 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 287 * you must call this function to drop all currently held locks and 288 * block until the contended lock becomes available. 289 * 290 * This function returns 0 on success, or -ERESTARTSYS if this context 291 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the 292 * wait has been interrupted. 293 */ 294 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 295 { 296 struct drm_modeset_lock *contended = ctx->contended; 297 298 ctx->contended = NULL; 299 300 if (WARN_ON(!contended)) 301 return 0; 302 303 drm_modeset_drop_locks(ctx); 304 305 return modeset_lock(contended, ctx, ctx->interruptible, true); 306 } 307 EXPORT_SYMBOL(drm_modeset_backoff); 308 309 /** 310 * drm_modeset_lock_init - initialize lock 311 * @lock: lock to init 312 */ 313 void drm_modeset_lock_init(struct drm_modeset_lock *lock) 314 { 315 ww_mutex_init(&lock->mutex, &crtc_ww_class); 316 INIT_LIST_HEAD(&lock->head); 317 } 318 EXPORT_SYMBOL(drm_modeset_lock_init); 319 320 /** 321 * drm_modeset_lock - take modeset lock 322 * @lock: lock to take 323 * @ctx: acquire ctx 324 * 325 * If @ctx is not NULL, then its ww acquire context is used and the 326 * lock will be tracked by the context and can be released by calling 327 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 328 * deadlock scenario has been detected and it is an error to attempt 329 * to take any more locks without first calling drm_modeset_backoff(). 330 * 331 * If the @ctx is not NULL and initialized with 332 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with 333 * -ERESTARTSYS when interrupted. 334 * 335 * If @ctx is NULL then the function call behaves like a normal, 336 * uninterruptible non-nesting mutex_lock() call. 337 */ 338 int drm_modeset_lock(struct drm_modeset_lock *lock, 339 struct drm_modeset_acquire_ctx *ctx) 340 { 341 if (ctx) 342 return modeset_lock(lock, ctx, ctx->interruptible, false); 343 344 ww_mutex_lock(&lock->mutex, NULL); 345 return 0; 346 } 347 EXPORT_SYMBOL(drm_modeset_lock); 348 349 /** 350 * drm_modeset_lock_single_interruptible - take a single modeset lock 351 * @lock: lock to take 352 * 353 * This function behaves as drm_modeset_lock() with a NULL context, 354 * but performs interruptible waits. 355 * 356 * This function returns 0 on success, or -ERESTARTSYS when interrupted. 357 */ 358 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock) 359 { 360 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 361 } 362 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible); 363 364 /** 365 * drm_modeset_unlock - drop modeset lock 366 * @lock: lock to release 367 */ 368 void drm_modeset_unlock(struct drm_modeset_lock *lock) 369 { 370 list_del_init(&lock->head); 371 ww_mutex_unlock(&lock->mutex); 372 } 373 EXPORT_SYMBOL(drm_modeset_unlock); 374 375 /** 376 * drm_modeset_lock_all_ctx - take all modeset locks 377 * @dev: DRM device 378 * @ctx: lock acquisition context 379 * 380 * This function takes all modeset locks, suitable where a more fine-grained 381 * scheme isn't (yet) implemented. 382 * 383 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 384 * since that lock isn't required for modeset state changes. Callers which 385 * need to grab that lock too need to do so outside of the acquire context 386 * @ctx. 387 * 388 * Locks acquired with this function should be released by calling the 389 * drm_modeset_drop_locks() function on @ctx. 390 * 391 * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() 392 * 393 * Returns: 0 on success or a negative error-code on failure. 394 */ 395 int drm_modeset_lock_all_ctx(struct drm_device *dev, 396 struct drm_modeset_acquire_ctx *ctx) 397 { 398 struct drm_private_obj *privobj; 399 struct drm_crtc *crtc; 400 struct drm_plane *plane; 401 int ret; 402 403 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 404 if (ret) 405 return ret; 406 407 drm_for_each_crtc(crtc, dev) { 408 ret = drm_modeset_lock(&crtc->mutex, ctx); 409 if (ret) 410 return ret; 411 } 412 413 drm_for_each_plane(plane, dev) { 414 ret = drm_modeset_lock(&plane->mutex, ctx); 415 if (ret) 416 return ret; 417 } 418 419 drm_for_each_privobj(privobj, dev) { 420 ret = drm_modeset_lock(&privobj->lock, ctx); 421 if (ret) 422 return ret; 423 } 424 425 return 0; 426 } 427 EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 428