1/* $NetBSD: drm_modeset_lock.c,v 1.5 2021/12/18 23:44:57 riastradh Exp $ */ 2 3/* 4 * Copyright (C) 2014 Red Hat 5 * Author: Rob Clark <robdclark@gmail.com> 6 * 7 * Permission is hereby granted, free of charge, to any person obtaining a 8 * copy of this software and associated documentation files (the "Software"), 9 * to deal in the Software without restriction, including without limitation 10 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 11 * and/or sell copies of the Software, and to permit persons to whom the 12 * Software is furnished to do so, subject to the following conditions: 13 * 14 * The above copyright notice and this permission notice shall be included in 15 * all copies or substantial portions of the Software. 16 * 17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 20 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR 21 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, 22 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR 23 * OTHER DEALINGS IN THE SOFTWARE. 24 */ 25 26#include <sys/cdefs.h> 27__KERNEL_RCSID(0, "$NetBSD: drm_modeset_lock.c,v 1.5 2021/12/18 23:44:57 riastradh Exp $"); 28 29#include <drm/drm_atomic.h> 30#include <drm/drm_crtc.h> 31#include <drm/drm_device.h> 32#include <drm/drm_modeset_lock.h> 33 34/** 35 * DOC: kms locking 36 * 37 * As KMS moves toward more fine grained locking, and atomic ioctl where 38 * userspace can indirectly control locking order, it becomes necessary 39 * to use &ww_mutex and acquire-contexts to avoid deadlocks. But because 40 * the locking is more distributed around the driver code, we want a bit 41 * of extra utility/tracking out of our acquire-ctx. This is provided 42 * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx. 43 * 44 * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.rst 45 * 46 * The basic usage pattern is to:: 47 * 48 * drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 49 * retry: 50 * foreach (lock in random_ordered_set_of_locks) { 51 * ret = drm_modeset_lock(lock, ctx) 52 * if (ret == -EDEADLK) { 53 * ret = drm_modeset_backoff(ctx); 54 * if (!ret) 55 * goto retry; 56 * } 57 * if (ret) 58 * goto out; 59 * } 60 * ... do stuff ... 61 * out: 62 * drm_modeset_drop_locks(ctx); 63 * drm_modeset_acquire_fini(ctx); 64 * 65 * For convenience this control flow is implemented in 66 * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case 67 * where all modeset locks need to be taken through drm_modeset_lock_all_ctx(). 68 * 69 * If all that is needed is a single modeset lock, then the &struct 70 * drm_modeset_acquire_ctx is not needed and the locking can be simplified 71 * by passing a NULL instead of ctx in the drm_modeset_lock() call or 72 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards 73 * call drm_modeset_unlock(). 74 * 75 * On top of these per-object locks using &ww_mutex there's also an overall 76 * &drm_mode_config.mutex, for protecting everything else. Mostly this means 77 * probe state of connectors, and preventing hotplug add/removal of connectors. 78 * 79 * Finally there's a bunch of dedicated locks to protect drm core internal 80 * lists and lookup data structures. 81 */ 82 83static DEFINE_WW_CLASS(crtc_ww_class); 84 85/** 86 * drm_modeset_lock_all - take all modeset locks 87 * @dev: DRM device 88 * 89 * This function takes all modeset locks, suitable where a more fine-grained 90 * scheme isn't (yet) implemented. Locks must be dropped by calling the 91 * drm_modeset_unlock_all() function. 92 * 93 * This function is deprecated. It allocates a lock acquisition context and 94 * stores it in &drm_device.mode_config. This facilitate conversion of 95 * existing code because it removes the need to manually deal with the 96 * acquisition context, but it is also brittle because the context is global 97 * and care must be taken not to nest calls. New code should use the 98 * drm_modeset_lock_all_ctx() function and pass in the context explicitly. 99 */ 100void drm_modeset_lock_all(struct drm_device *dev) 101{ 102 struct drm_mode_config *config = &dev->mode_config; 103 struct drm_modeset_acquire_ctx *ctx; 104 int ret; 105 106 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL); 107 if (WARN_ON(!ctx)) 108 return; 109 110 mutex_lock(&config->mutex); 111 112 drm_modeset_acquire_init(ctx, 0); 113 114retry: 115 ret = drm_modeset_lock_all_ctx(dev, ctx); 116 if (ret < 0) { 117 if (ret == -EDEADLK) { 118 drm_modeset_backoff(ctx); 119 goto retry; 120 } 121 122 drm_modeset_acquire_fini(ctx); 123 kfree(ctx); 124 return; 125 } 126 ww_acquire_done(&ctx->ww_ctx); 127 128 WARN_ON(config->acquire_ctx); 129 130 /* 131 * We hold the locks now, so it is safe to stash the acquisition 132 * context for drm_modeset_unlock_all(). 133 */ 134 config->acquire_ctx = ctx; 135 136 drm_warn_on_modeset_not_all_locked(dev); 137} 138EXPORT_SYMBOL(drm_modeset_lock_all); 139 140/** 141 * drm_modeset_unlock_all - drop all modeset locks 142 * @dev: DRM device 143 * 144 * This function drops all modeset locks taken by a previous call to the 145 * drm_modeset_lock_all() function. 146 * 147 * This function is deprecated. It uses the lock acquisition context stored 148 * in &drm_device.mode_config. This facilitates conversion of existing 149 * code because it removes the need to manually deal with the acquisition 150 * context, but it is also brittle because the context is global and care must 151 * be taken not to nest calls. New code should pass the acquisition context 152 * directly to the drm_modeset_drop_locks() function. 153 */ 154void drm_modeset_unlock_all(struct drm_device *dev) 155{ 156 struct drm_mode_config *config = &dev->mode_config; 157 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; 158 159 if (WARN_ON(!ctx)) 160 return; 161 162 config->acquire_ctx = NULL; 163 drm_modeset_drop_locks(ctx); 164 drm_modeset_acquire_fini(ctx); 165 166 kfree(ctx); 167 168 mutex_unlock(&dev->mode_config.mutex); 169} 170EXPORT_SYMBOL(drm_modeset_unlock_all); 171 172/** 173 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked 174 * @dev: device 175 * 176 * Useful as a debug assert. 177 */ 178void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) 179{ 180 struct drm_crtc *crtc; 181 182 /* Locking is currently fubar in the panic handler. */ 183 if (oops_in_progress) 184 return; 185 186 drm_for_each_crtc(crtc, dev) 187 WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); 188 189 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 190 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); 191} 192EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); 193 194/** 195 * drm_modeset_acquire_init - initialize acquire context 196 * @ctx: the acquire context 197 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE 198 * 199 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags, 200 * all calls to drm_modeset_lock() will perform an interruptible 201 * wait. 202 */ 203void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, 204 uint32_t flags) 205{ 206 memset(ctx, 0, sizeof(*ctx)); 207 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 208 INIT_LIST_HEAD(&ctx->locked); 209 210 if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE) 211 ctx->interruptible = true; 212} 213EXPORT_SYMBOL(drm_modeset_acquire_init); 214 215/** 216 * drm_modeset_acquire_fini - cleanup acquire context 217 * @ctx: the acquire context 218 */ 219void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 220{ 221 ww_acquire_fini(&ctx->ww_ctx); 222} 223EXPORT_SYMBOL(drm_modeset_acquire_fini); 224 225/** 226 * drm_modeset_drop_locks - drop all locks 227 * @ctx: the acquire context 228 * 229 * Drop all locks currently held against this acquire context. 230 */ 231void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 232{ 233 WARN_ON(ctx->contended); 234 while (!list_empty(&ctx->locked)) { 235 struct drm_modeset_lock *lock; 236 237 lock = list_first_entry(&ctx->locked, 238 struct drm_modeset_lock, head); 239 240 drm_modeset_unlock(lock); 241 } 242} 243EXPORT_SYMBOL(drm_modeset_drop_locks); 244 245static inline int modeset_lock(struct drm_modeset_lock *lock, 246 struct drm_modeset_acquire_ctx *ctx, 247 bool interruptible, bool slow) 248{ 249 int ret; 250 251 WARN_ON(ctx->contended); 252 253 if (ctx->trylock_only) { 254 lockdep_assert_held(&ctx->ww_ctx); 255 256 if (!ww_mutex_trylock(&lock->mutex)) 257 return -EBUSY; 258 else 259 return 0; 260 } else if (interruptible && slow) { 261 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 262 } else if (interruptible) { 263 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 264 } else if (slow) { 265 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 266 ret = 0; 267 } else { 268 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 269 } 270 if (!ret) { 271 WARN_ON(!list_empty(&lock->head)); 272 list_add(&lock->head, &ctx->locked); 273 } else if (ret == -EALREADY) { 274 /* we already hold the lock.. this is fine. For atomic 275 * we will need to be able to drm_modeset_lock() things 276 * without having to keep track of what is already locked 277 * or not. 278 */ 279 ret = 0; 280 } else if (ret == -EDEADLK) { 281 ctx->contended = lock; 282 } 283 284 return ret; 285} 286 287/** 288 * drm_modeset_backoff - deadlock avoidance backoff 289 * @ctx: the acquire context 290 * 291 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 292 * you must call this function to drop all currently held locks and 293 * block until the contended lock becomes available. 294 * 295 * This function returns 0 on success, or -ERESTARTSYS if this context 296 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the 297 * wait has been interrupted. 298 */ 299int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 300{ 301 struct drm_modeset_lock *contended = ctx->contended; 302 303 ctx->contended = NULL; 304 305 if (WARN_ON(!contended)) 306 return 0; 307 308 drm_modeset_drop_locks(ctx); 309 310 return modeset_lock(contended, ctx, ctx->interruptible, true); 311} 312EXPORT_SYMBOL(drm_modeset_backoff); 313 314/** 315 * drm_modeset_lock_init - initialize lock 316 * @lock: lock to init 317 */ 318void drm_modeset_lock_init(struct drm_modeset_lock *lock) 319{ 320 ww_mutex_init(&lock->mutex, &crtc_ww_class); 321 INIT_LIST_HEAD(&lock->head); 322} 323EXPORT_SYMBOL(drm_modeset_lock_init); 324 325/** 326 * drm_modeset_lock - take modeset lock 327 * @lock: lock to take 328 * @ctx: acquire ctx 329 * 330 * If @ctx is not NULL, then its ww acquire context is used and the 331 * lock will be tracked by the context and can be released by calling 332 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 333 * deadlock scenario has been detected and it is an error to attempt 334 * to take any more locks without first calling drm_modeset_backoff(). 335 * 336 * If the @ctx is not NULL and initialized with 337 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with 338 * -ERESTARTSYS when interrupted. 339 * 340 * If @ctx is NULL then the function call behaves like a normal, 341 * uninterruptible non-nesting mutex_lock() call. 342 */ 343int drm_modeset_lock(struct drm_modeset_lock *lock, 344 struct drm_modeset_acquire_ctx *ctx) 345{ 346 if (ctx) 347 return modeset_lock(lock, ctx, ctx->interruptible, false); 348 349 ww_mutex_lock(&lock->mutex, NULL); 350 return 0; 351} 352EXPORT_SYMBOL(drm_modeset_lock); 353 354/** 355 * drm_modeset_lock_single_interruptible - take a single modeset lock 356 * @lock: lock to take 357 * 358 * This function behaves as drm_modeset_lock() with a NULL context, 359 * but performs interruptible waits. 360 * 361 * This function returns 0 on success, or -ERESTARTSYS when interrupted. 362 */ 363int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock) 364{ 365 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 366} 367EXPORT_SYMBOL(drm_modeset_lock_single_interruptible); 368 369/** 370 * drm_modeset_unlock - drop modeset lock 371 * @lock: lock to release 372 */ 373void drm_modeset_unlock(struct drm_modeset_lock *lock) 374{ 375 list_del_init(&lock->head); 376 ww_mutex_unlock(&lock->mutex); 377} 378EXPORT_SYMBOL(drm_modeset_unlock); 379 380/** 381 * drm_modeset_lock_all_ctx - take all modeset locks 382 * @dev: DRM device 383 * @ctx: lock acquisition context 384 * 385 * This function takes all modeset locks, suitable where a more fine-grained 386 * scheme isn't (yet) implemented. 387 * 388 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex 389 * since that lock isn't required for modeset state changes. Callers which 390 * need to grab that lock too need to do so outside of the acquire context 391 * @ctx. 392 * 393 * Locks acquired with this function should be released by calling the 394 * drm_modeset_drop_locks() function on @ctx. 395 * 396 * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() 397 * 398 * Returns: 0 on success or a negative error-code on failure. 399 */ 400int drm_modeset_lock_all_ctx(struct drm_device *dev, 401 struct drm_modeset_acquire_ctx *ctx) 402{ 403 struct drm_private_obj *privobj; 404 struct drm_crtc *crtc; 405 struct drm_plane *plane; 406 int ret; 407 408 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); 409 if (ret) 410 return ret; 411 412 drm_for_each_crtc(crtc, dev) { 413 ret = drm_modeset_lock(&crtc->mutex, ctx); 414 if (ret) 415 return ret; 416 } 417 418 drm_for_each_plane(plane, dev) { 419 ret = drm_modeset_lock(&plane->mutex, ctx); 420 if (ret) 421 return ret; 422 } 423 424 drm_for_each_privobj(privobj, dev) { 425 ret = drm_modeset_lock(&privobj->lock, ctx); 426 if (ret) 427 return ret; 428 } 429 430 return 0; 431} 432EXPORT_SYMBOL(drm_modeset_lock_all_ctx); 433