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 * For convenience this control flow is implemented in 60 * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case 61 * where all modeset locks need to be taken through drm_modeset_lock_all_ctx(). 62 * 63 * If all that is needed is a single modeset lock, then the &struct 64 * drm_modeset_acquire_ctx is not needed and the locking can be simplified 65 * by passing a NULL instead of ctx in the drm_modeset_lock() call or 66 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards 67 * call drm_modeset_unlock(). 68 * 69 * On top of these per-object locks using &ww_mutex there's also an overall 70 * &drm_mode_config.mutex, for protecting everything else. Mostly this means 71 * probe state of connectors, and preventing hotplug add/removal of connectors. 72 * 73 * Finally there's a bunch of dedicated locks to protect drm core internal 74 * lists and lookup data structures. 75 */ 76 77 static DEFINE_WW_CLASS(crtc_ww_class); 78 79 /** 80 * drm_modeset_lock_all - take all modeset locks 81 * @dev: DRM device 82 * 83 * This function takes all modeset locks, suitable where a more fine-grained 84 * scheme isn't (yet) implemented. Locks must be dropped by calling the 85 * drm_modeset_unlock_all() function. 86 * 87 * This function is deprecated. It allocates a lock acquisition context and 88 * stores it in &drm_device.mode_config. This facilitate conversion of 89 * existing code because it removes the need to manually deal with the 90 * acquisition context, but it is also brittle because the context is global 91 * and care must be taken not to nest calls. New code should use the 92 * drm_modeset_lock_all_ctx() function and pass in the context explicitly. 93 */ 94 void drm_modeset_lock_all(struct drm_device *dev) 95 { 96 struct drm_mode_config *config = &dev->mode_config; 97 struct drm_modeset_acquire_ctx *ctx; 98 int ret; 99 100 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL); 101 if (WARN_ON(!ctx)) 102 return; 103 104 mutex_lock(&config->mutex); 105 106 drm_modeset_acquire_init(ctx, 0); 107 108 retry: 109 ret = drm_modeset_lock_all_ctx(dev, ctx); 110 if (ret < 0) { 111 if (ret == -EDEADLK) { 112 drm_modeset_backoff(ctx); 113 goto retry; 114 } 115 116 drm_modeset_acquire_fini(ctx); 117 kfree(ctx); 118 return; 119 } 120 ww_acquire_done(&ctx->ww_ctx); 121 122 WARN_ON(config->acquire_ctx); 123 124 /* 125 * We hold the locks now, so it is safe to stash the acquisition 126 * context for drm_modeset_unlock_all(). 127 */ 128 config->acquire_ctx = ctx; 129 130 drm_warn_on_modeset_not_all_locked(dev); 131 } 132 EXPORT_SYMBOL(drm_modeset_lock_all); 133 134 /** 135 * drm_modeset_unlock_all - drop all modeset locks 136 * @dev: DRM device 137 * 138 * This function drops all modeset locks taken by a previous call to the 139 * drm_modeset_lock_all() function. 140 * 141 * This function is deprecated. It uses the lock acquisition context stored 142 * in &drm_device.mode_config. This facilitates conversion of existing 143 * code because it removes the need to manually deal with the acquisition 144 * context, but it is also brittle because the context is global and care must 145 * be taken not to nest calls. New code should pass the acquisition context 146 * directly to the drm_modeset_drop_locks() function. 147 */ 148 void drm_modeset_unlock_all(struct drm_device *dev) 149 { 150 struct drm_mode_config *config = &dev->mode_config; 151 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 152 153 if (WARN_ON(!ctx)) 154 return; 155 156 config->acquire_ctx = NULL; 157 drm_modeset_drop_locks(ctx); 158 drm_modeset_acquire_fini(ctx); 159 160 kfree(ctx); 161 162 mutex_unlock(&dev->mode_config.mutex); 163 } 164 EXPORT_SYMBOL(drm_modeset_unlock_all); 165 166 /** 167 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 168 * @dev: device 169 * 170 * Useful as a debug assert. 171 */ 172 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 173 { 174 struct drm_crtc *crtc; 175 176 /* Locking is currently fubar in the panic handler. */ 177 if (oops_in_progress) 178 return; 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 *lock; 230 231 lock = list_first_entry(&ctx->locked, 232 struct drm_modeset_lock, head); 233 234 drm_modeset_unlock(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 lockdep_assert_held(&ctx->ww_ctx); 249 250 if (!ww_mutex_trylock(&lock->mutex)) 251 return -EBUSY; 252 else 253 return 0; 254 } else if (interruptible && slow) { 255 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 256 } else if (interruptible) { 257 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 258 } else if (slow) { 259 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 260 ret = 0; 261 } else { 262 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 263 } 264 if (!ret) { 265 WARN_ON(!list_empty(&lock->head)); 266 list_add(&lock->head, &ctx->locked); 267 } else if (ret == -EALREADY) { 268 /* we already hold the lock.. this is fine. For atomic 269 * we will need to be able to drm_modeset_lock() things 270 * without having to keep track of what is already locked 271 * or not. 272 */ 273 ret = 0; 274 } else if (ret == -EDEADLK) { 275 ctx->contended = lock; 276 } 277 278 return ret; 279 } 280 281 /** 282 * drm_modeset_backoff - deadlock avoidance backoff 283 * @ctx: the acquire context 284 * 285 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 286 * you must call this function to drop all currently held locks and 287 * block until the contended lock becomes available. 288 * 289 * This function returns 0 on success, or -ERESTARTSYS if this context 290 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the 291 * wait has been interrupted. 292 */ 293 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 294 { 295 struct drm_modeset_lock *contended = ctx->contended; 296 297 ctx->contended = NULL; 298 299 if (WARN_ON(!contended)) 300 return 0; 301 302 drm_modeset_drop_locks(ctx); 303 304 return modeset_lock(contended, ctx, ctx->interruptible, true); 305 } 306 EXPORT_SYMBOL(drm_modeset_backoff); 307 308 /** 309 * drm_modeset_lock_init - initialize lock 310 * @lock: lock to init 311 */ 312 void drm_modeset_lock_init(struct drm_modeset_lock *lock) 313 { 314 ww_mutex_init(&lock->mutex, &crtc_ww_class); 315 INIT_LIST_HEAD(&lock->head); 316 } 317 EXPORT_SYMBOL(drm_modeset_lock_init); 318 319 /** 320 * drm_modeset_lock - take modeset lock 321 * @lock: lock to take 322 * @ctx: acquire ctx 323 * 324 * If @ctx is not NULL, then its ww acquire context is used and the 325 * lock will be tracked by the context and can be released by calling 326 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 327 * deadlock scenario has been detected and it is an error to attempt 328 * to take any more locks without first calling drm_modeset_backoff(). 329 * 330 * If the @ctx is not NULL and initialized with 331 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with 332 * -ERESTARTSYS when interrupted. 333 * 334 * If @ctx is NULL then the function call behaves like a normal, 335 * uninterruptible non-nesting mutex_lock() call. 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, ctx->interruptible, 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_single_interruptible - take a single modeset lock 350 * @lock: lock to take 351 * 352 * This function behaves as drm_modeset_lock() with a NULL context, 353 * but performs interruptible waits. 354 * 355 * This function returns 0 on success, or -ERESTARTSYS when interrupted. 356 */ 357 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock) 358 { 359 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 360 } 361 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible); 362 363 /** 364 * drm_modeset_unlock - drop modeset lock 365 * @lock: lock to release 366 */ 367 void drm_modeset_unlock(struct drm_modeset_lock *lock) 368 { 369 list_del_init(&lock->head); 370 ww_mutex_unlock(&lock->mutex); 371 } 372 EXPORT_SYMBOL(drm_modeset_unlock); 373 374 /** 375 * drm_modeset_lock_all_ctx - take all modeset locks 376 * @dev: DRM device 377 * @ctx: lock acquisition context 378 * 379 * This function takes all modeset locks, suitable where a more fine-grained 380 * scheme isn't (yet) implemented. 381 * 382 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 383 * since that lock isn't required for modeset state changes. Callers which 384 * need to grab that lock too need to do so outside of the acquire context 385 * @ctx. 386 * 387 * Locks acquired with this function should be released by calling the 388 * drm_modeset_drop_locks() function on @ctx. 389 * 390 * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() 391 * 392 * Returns: 0 on success or a negative error-code on failure. 393 */ 394 int drm_modeset_lock_all_ctx(struct drm_device *dev, 395 struct drm_modeset_acquire_ctx *ctx) 396 { 397 struct drm_crtc *crtc; 398 struct drm_plane *plane; 399 int ret; 400 401 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 402 if (ret) 403 return ret; 404 405 drm_for_each_crtc(crtc, dev) { 406 ret = drm_modeset_lock(&crtc->mutex, ctx); 407 if (ret) 408 return ret; 409 } 410 411 drm_for_each_plane(plane, dev) { 412 ret = drm_modeset_lock(&plane->mutex, ctx); 413 if (ret) 414 return ret; 415 } 416 417 return 0; 418 } 419 EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 420