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