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 ww_acquire_done(&ctx->ww_ctx); 117 118 WARN_ON(config->acquire_ctx); 119 120 /* 121 * We hold the locks now, so it is safe to stash the acquisition 122 * context for drm_modeset_unlock_all(). 123 */ 124 config->acquire_ctx = ctx; 125 126 drm_warn_on_modeset_not_all_locked(dev); 127 } 128 EXPORT_SYMBOL(drm_modeset_lock_all); 129 130 /** 131 * drm_modeset_unlock_all - drop all modeset locks 132 * @dev: DRM device 133 * 134 * This function drops all modeset locks taken by a previous call to the 135 * drm_modeset_lock_all() function. 136 * 137 * This function is deprecated. It uses the lock acquisition context stored 138 * in &drm_device.mode_config. This facilitates conversion of existing 139 * code because it removes the need to manually deal with the acquisition 140 * context, but it is also brittle because the context is global and care must 141 * be taken not to nest calls. New code should pass the acquisition context 142 * directly to the drm_modeset_drop_locks() function. 143 */ 144 void drm_modeset_unlock_all(struct drm_device *dev) 145 { 146 struct drm_mode_config *config = &dev->mode_config; 147 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 148 149 if (WARN_ON(!ctx)) 150 return; 151 152 config->acquire_ctx = NULL; 153 drm_modeset_drop_locks(ctx); 154 drm_modeset_acquire_fini(ctx); 155 156 kfree(ctx); 157 158 mutex_unlock(&dev->mode_config.mutex); 159 } 160 EXPORT_SYMBOL(drm_modeset_unlock_all); 161 162 /** 163 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 164 * @dev: device 165 * 166 * Useful as a debug assert. 167 */ 168 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 169 { 170 struct drm_crtc *crtc; 171 172 /* Locking is currently fubar in the panic handler. */ 173 if (oops_in_progress) 174 return; 175 176 drm_for_each_crtc(crtc, dev) 177 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 178 179 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 180 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 181 } 182 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 183 184 /** 185 * drm_modeset_acquire_init - initialize acquire context 186 * @ctx: the acquire context 187 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE 188 * 189 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags, 190 * all calls to drm_modeset_lock() will perform an interruptible 191 * wait. 192 */ 193 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 194 uint32_t flags) 195 { 196 memset(ctx, 0, sizeof(*ctx)); 197 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 198 INIT_LIST_HEAD(&ctx->locked); 199 200 if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 201 ctx->interruptible = true; 202 } 203 EXPORT_SYMBOL(drm_modeset_acquire_init); 204 205 /** 206 * drm_modeset_acquire_fini - cleanup acquire context 207 * @ctx: the acquire context 208 */ 209 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 210 { 211 ww_acquire_fini(&ctx->ww_ctx); 212 } 213 EXPORT_SYMBOL(drm_modeset_acquire_fini); 214 215 /** 216 * drm_modeset_drop_locks - drop all locks 217 * @ctx: the acquire context 218 * 219 * Drop all locks currently held against this acquire context. 220 */ 221 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 222 { 223 WARN_ON(ctx->contended); 224 while (!list_empty(&ctx->locked)) { 225 struct drm_modeset_lock *lock; 226 227 lock = list_first_entry(&ctx->locked, 228 struct drm_modeset_lock, head); 229 230 drm_modeset_unlock(lock); 231 } 232 } 233 EXPORT_SYMBOL(drm_modeset_drop_locks); 234 235 static inline int modeset_lock(struct drm_modeset_lock *lock, 236 struct drm_modeset_acquire_ctx *ctx, 237 bool interruptible, bool slow) 238 { 239 int ret; 240 241 WARN_ON(ctx->contended); 242 243 if (ctx->trylock_only) { 244 lockdep_assert_held(&ctx->ww_ctx); 245 246 if (!ww_mutex_trylock(&lock->mutex)) 247 return -EBUSY; 248 else 249 return 0; 250 } else if (interruptible && slow) { 251 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 252 } else if (interruptible) { 253 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 254 } else if (slow) { 255 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 256 ret = 0; 257 } else { 258 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 259 } 260 if (!ret) { 261 WARN_ON(!list_empty(&lock->head)); 262 list_add(&lock->head, &ctx->locked); 263 } else if (ret == -EALREADY) { 264 /* we already hold the lock.. this is fine. For atomic 265 * we will need to be able to drm_modeset_lock() things 266 * without having to keep track of what is already locked 267 * or not. 268 */ 269 ret = 0; 270 } else if (ret == -EDEADLK) { 271 ctx->contended = lock; 272 } 273 274 return ret; 275 } 276 277 /** 278 * drm_modeset_backoff - deadlock avoidance backoff 279 * @ctx: the acquire context 280 * 281 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 282 * you must call this function to drop all currently held locks and 283 * block until the contended lock becomes available. 284 * 285 * This function returns 0 on success, or -ERESTARTSYS if this context 286 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the 287 * wait has been interrupted. 288 */ 289 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 290 { 291 struct drm_modeset_lock *contended = ctx->contended; 292 293 ctx->contended = NULL; 294 295 if (WARN_ON(!contended)) 296 return 0; 297 298 drm_modeset_drop_locks(ctx); 299 300 return modeset_lock(contended, ctx, ctx->interruptible, true); 301 } 302 EXPORT_SYMBOL(drm_modeset_backoff); 303 304 /** 305 * drm_modeset_lock_init - initialize lock 306 * @lock: lock to init 307 */ 308 void drm_modeset_lock_init(struct drm_modeset_lock *lock) 309 { 310 ww_mutex_init(&lock->mutex, &crtc_ww_class); 311 INIT_LIST_HEAD(&lock->head); 312 } 313 EXPORT_SYMBOL(drm_modeset_lock_init); 314 315 /** 316 * drm_modeset_lock - take modeset lock 317 * @lock: lock to take 318 * @ctx: acquire ctx 319 * 320 * If @ctx is not NULL, then its ww acquire context is used and the 321 * lock will be tracked by the context and can be released by calling 322 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 323 * deadlock scenario has been detected and it is an error to attempt 324 * to take any more locks without first calling drm_modeset_backoff(). 325 * 326 * If the @ctx is not NULL and initialized with 327 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with 328 * -ERESTARTSYS when interrupted. 329 * 330 * If @ctx is NULL then the function call behaves like a normal, 331 * uninterruptible non-nesting mutex_lock() call. 332 */ 333 int drm_modeset_lock(struct drm_modeset_lock *lock, 334 struct drm_modeset_acquire_ctx *ctx) 335 { 336 if (ctx) 337 return modeset_lock(lock, ctx, ctx->interruptible, false); 338 339 ww_mutex_lock(&lock->mutex, NULL); 340 return 0; 341 } 342 EXPORT_SYMBOL(drm_modeset_lock); 343 344 /** 345 * drm_modeset_lock_single_interruptible - take a single modeset lock 346 * @lock: lock to take 347 * 348 * This function behaves as drm_modeset_lock() with a NULL context, 349 * but performs interruptible waits. 350 * 351 * This function returns 0 on success, or -ERESTARTSYS when interrupted. 352 */ 353 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock) 354 { 355 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 356 } 357 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible); 358 359 /** 360 * drm_modeset_unlock - drop modeset lock 361 * @lock: lock to release 362 */ 363 void drm_modeset_unlock(struct drm_modeset_lock *lock) 364 { 365 list_del_init(&lock->head); 366 ww_mutex_unlock(&lock->mutex); 367 } 368 EXPORT_SYMBOL(drm_modeset_unlock); 369 370 /** 371 * drm_modeset_lock_all_ctx - take all modeset locks 372 * @dev: DRM device 373 * @ctx: lock acquisition context 374 * 375 * This function takes all modeset locks, suitable where a more fine-grained 376 * scheme isn't (yet) implemented. 377 * 378 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 379 * since that lock isn't required for modeset state changes. Callers which 380 * need to grab that lock too need to do so outside of the acquire context 381 * @ctx. 382 * 383 * Locks acquired with this function should be released by calling the 384 * drm_modeset_drop_locks() function on @ctx. 385 * 386 * Returns: 0 on success or a negative error-code on failure. 387 */ 388 int drm_modeset_lock_all_ctx(struct drm_device *dev, 389 struct drm_modeset_acquire_ctx *ctx) 390 { 391 struct drm_crtc *crtc; 392 struct drm_plane *plane; 393 int ret; 394 395 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 396 if (ret) 397 return ret; 398 399 drm_for_each_crtc(crtc, dev) { 400 ret = drm_modeset_lock(&crtc->mutex, ctx); 401 if (ret) 402 return ret; 403 } 404 405 drm_for_each_plane(plane, dev) { 406 ret = drm_modeset_lock(&plane->mutex, ctx); 407 if (ret) 408 return ret; 409 } 410 411 return 0; 412 } 413 EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 414