drivers/gpu/drm/drm_modeset_lock.c

   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 drm_modeset_lock / 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)
  43  *   retry:
  44  *     foreach (lock in random_ordered_set_of_locks) {
  45  *       ret = drm_modeset_lock(lock, &ctx)
  46  *       if (ret == -EDEADLK) {
  47  *          drm_modeset_backoff(&ctx);
  48  *          goto retry;
  49  *       }
  50  *     }
  51  *
  52  *     ... do stuff ...
  53  *
  54  *     drm_modeset_drop_locks(&ctx);
  55  *     drm_modeset_acquire_fini(&ctx);
  56  */
  57
  58
  59 /**
  60  * __drm_modeset_lock_all - internal helper to grab all modeset locks
  61  * @dev: DRM device
  62  * @trylock: trylock mode for atomic contexts
  63  *
  64  * This is a special version of drm_modeset_lock_all() which can also be used in
  65  * atomic contexts. Then @trylock must be set to true.
  66  *
  67  * Returns:
  68  * 0 on success or negative error code on failure.
  69  */
  70 int __drm_modeset_lock_all(struct drm_device *dev,
  71                            bool trylock)
  72 {
  73         struct drm_mode_config *config = &dev->mode_config;
  74         struct drm_modeset_acquire_ctx *ctx;
  75         int ret;
  76
  77         ctx = kzalloc(sizeof(*ctx),
  78                       trylock ? GFP_ATOMIC : GFP_KERNEL);
  79         if (!ctx)
  80                 return -ENOMEM;
  81
  82         if (trylock) {
  83                 if (!mutex_trylock(&config->mutex)) {
  84                         ret = -EBUSY;
  85                         goto out;
  86                 }
  87         } else {
  88                 mutex_lock(&config->mutex);
  89         }
  90
  91         drm_modeset_acquire_init(ctx, 0);
  92         ctx->trylock_only = trylock;
  93
  94 retry:
  95         ret = drm_modeset_lock(&config->connection_mutex, ctx);
  96         if (ret)
  97                 goto fail;
  98         ret = drm_modeset_lock_all_crtcs(dev, ctx);
  99         if (ret)
 100                 goto fail;
 101
 102         WARN_ON(config->acquire_ctx);
 103
 104         /* now we hold the locks, so now that it is safe, stash the
 105          * ctx for drm_modeset_unlock_all():
 106          */
 107         config->acquire_ctx = ctx;
 108
 109         drm_warn_on_modeset_not_all_locked(dev);
 110
 111         return 0;
 112
 113 fail:
 114         if (ret == -EDEADLK) {
 115                 drm_modeset_backoff(ctx);
 116                 goto retry;
 117         }
 118
 119 out:
 120         kfree(ctx);
 121         return ret;
 122 }
 123 EXPORT_SYMBOL(__drm_modeset_lock_all);
 124
 125 /**
 126  * drm_modeset_lock_all - take all modeset locks
 127  * @dev: drm device
 128  *
 129  * This function takes all modeset locks, suitable where a more fine-grained
 130  * scheme isn't (yet) implemented. Locks must be dropped with
 131  * drm_modeset_unlock_all.
 132  */
 133 void drm_modeset_lock_all(struct drm_device *dev)
 134 {
 135         WARN_ON(__drm_modeset_lock_all(dev, false) != 0);
 136 }
 137 EXPORT_SYMBOL(drm_modeset_lock_all);
 138
 139 /**
 140  * drm_modeset_unlock_all - drop all modeset locks
 141  * @dev: device
 142  *
 143  * This function drop all modeset locks taken by drm_modeset_lock_all.
 144  */
 145 void drm_modeset_unlock_all(struct drm_device *dev)
 146 {
 147         struct drm_mode_config *config = &dev->mode_config;
 148         struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
 149
 150         if (WARN_ON(!ctx))
 151                 return;
 152
 153         config->acquire_ctx = NULL;
 154         drm_modeset_drop_locks(ctx);
 155         drm_modeset_acquire_fini(ctx);
 156
 157         kfree(ctx);
 158
 159         mutex_unlock(&dev->mode_config.mutex);
 160 }
 161 EXPORT_SYMBOL(drm_modeset_unlock_all);
 162
 163 /**
 164  * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
 165  * @crtc: DRM CRTC
 166  * @plane: DRM plane to be updated on @crtc
 167  *
 168  * This function locks the given crtc and plane (which should be either the
 169  * primary or cursor plane) using a hidden acquire context. This is necessary so
 170  * that drivers internally using the atomic interfaces can grab further locks
 171  * with the lock acquire context.
 172  *
 173  * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
 174  * converted to universal planes yet.
 175  */
 176 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
 177                            struct drm_plane *plane)
 178 {
 179         struct drm_modeset_acquire_ctx *ctx;
 180         int ret;
 181
 182         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 183         if (WARN_ON(!ctx))
 184                 return;
 185
 186         drm_modeset_acquire_init(ctx, 0);
 187
 188 retry:
 189         ret = drm_modeset_lock(&crtc->mutex, ctx);
 190         if (ret)
 191                 goto fail;
 192
 193         if (plane) {
 194                 ret = drm_modeset_lock(&plane->mutex, ctx);
 195                 if (ret)
 196                         goto fail;
 197
 198                 if (plane->crtc) {
 199                         ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
 200                         if (ret)
 201                                 goto fail;
 202                 }
 203         }
 204
 205         WARN_ON(crtc->acquire_ctx);
 206
 207         /* now we hold the locks, so now that it is safe, stash the
 208          * ctx for drm_modeset_unlock_crtc():
 209          */
 210         crtc->acquire_ctx = ctx;
 211
 212         return;
 213
 214 fail:
 215         if (ret == -EDEADLK) {
 216                 drm_modeset_backoff(ctx);
 217                 goto retry;
 218         }
 219 }
 220 EXPORT_SYMBOL(drm_modeset_lock_crtc);
 221
 222 /**
 223  * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
 224  * @crtc: drm crtc
 225  *
 226  * Legacy ioctl operations like cursor updates or page flips only have per-crtc
 227  * locking, and store the acquire ctx in the corresponding crtc. All other
 228  * legacy operations take all locks and use a global acquire context. This
 229  * function grabs the right one.
 230  */
 231 struct drm_modeset_acquire_ctx *
 232 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
 233 {
 234         if (crtc->acquire_ctx)
 235                 return crtc->acquire_ctx;
 236
 237         WARN_ON(!crtc->dev->mode_config.acquire_ctx);
 238
 239         return crtc->dev->mode_config.acquire_ctx;
 240 }
 241 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
 242
 243 /**
 244  * drm_modeset_unlock_crtc - drop crtc lock
 245  * @crtc: drm crtc
 246  *
 247  * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
 248  * locks acquired through the hidden context.
 249  */
 250 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
 251 {
 252         struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
 253
 254         if (WARN_ON(!ctx))
 255                 return;
 256
 257         crtc->acquire_ctx = NULL;
 258         drm_modeset_drop_locks(ctx);
 259         drm_modeset_acquire_fini(ctx);
 260
 261         kfree(ctx);
 262 }
 263 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
 264
 265 /**
 266  * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
 267  * @dev: device
 268  *
 269  * Useful as a debug assert.
 270  */
 271 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
 272 {
 273         struct drm_crtc *crtc;
 274
 275         /* Locking is currently fubar in the panic handler. */
 276         if (oops_in_progress)
 277                 return;
 278
 279         list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
 280                 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
 281
 282         WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
 283         WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
 284 }
 285 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
 286
 287 /**
 288  * drm_modeset_acquire_init - initialize acquire context
 289  * @ctx: the acquire context
 290  * @flags: for future
 291  */
 292 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 293                 uint32_t flags)
 294 {
 295         memset(ctx, 0, sizeof(*ctx));
 296         ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
 297         INIT_LIST_HEAD(&ctx->locked);
 298 }
 299 EXPORT_SYMBOL(drm_modeset_acquire_init);
 300
 301 /**
 302  * drm_modeset_acquire_fini - cleanup acquire context
 303  * @ctx: the acquire context
 304  */
 305 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
 306 {
 307         ww_acquire_fini(&ctx->ww_ctx);
 308 }
 309 EXPORT_SYMBOL(drm_modeset_acquire_fini);
 310
 311 /**
 312  * drm_modeset_drop_locks - drop all locks
 313  * @ctx: the acquire context
 314  *
 315  * Drop all locks currently held against this acquire context.
 316  */
 317 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
 318 {
 319         WARN_ON(ctx->contended);
 320         while (!list_empty(&ctx->locked)) {
 321                 struct drm_modeset_lock *lock;
 322
 323                 lock = list_first_entry(&ctx->locked,
 324                                 struct drm_modeset_lock, head);
 325
 326                 drm_modeset_unlock(lock);
 327         }
 328 }
 329 EXPORT_SYMBOL(drm_modeset_drop_locks);
 330
 331 static inline int modeset_lock(struct drm_modeset_lock *lock,
 332                 struct drm_modeset_acquire_ctx *ctx,
 333                 bool interruptible, bool slow)
 334 {
 335         int ret;
 336
 337         WARN_ON(ctx->contended);
 338
 339         if (ctx->trylock_only) {
 340                 if (!ww_mutex_trylock(&lock->mutex))
 341                         return -EBUSY;
 342                 else
 343                         return 0;
 344         } else if (interruptible && slow) {
 345                 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
 346         } else if (interruptible) {
 347                 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
 348         } else if (slow) {
 349                 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
 350                 ret = 0;
 351         } else {
 352                 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
 353         }
 354         if (!ret) {
 355                 WARN_ON(!list_empty(&lock->head));
 356                 list_add(&lock->head, &ctx->locked);
 357         } else if (ret == -EALREADY) {
 358                 /* we already hold the lock.. this is fine.  For atomic
 359                  * we will need to be able to drm_modeset_lock() things
 360                  * without having to keep track of what is already locked
 361                  * or not.
 362                  */
 363                 ret = 0;
 364         } else if (ret == -EDEADLK) {
 365                 ctx->contended = lock;
 366         }
 367
 368         return ret;
 369 }
 370
 371 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
 372                 bool interruptible)
 373 {
 374         struct drm_modeset_lock *contended = ctx->contended;
 375
 376         ctx->contended = NULL;
 377
 378         if (WARN_ON(!contended))
 379                 return 0;
 380
 381         drm_modeset_drop_locks(ctx);
 382
 383         return modeset_lock(contended, ctx, interruptible, true);
 384 }
 385
 386 /**
 387  * drm_modeset_backoff - deadlock avoidance backoff
 388  * @ctx: the acquire context
 389  *
 390  * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
 391  * you must call this function to drop all currently held locks and
 392  * block until the contended lock becomes available.
 393  */
 394 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
 395 {
 396         modeset_backoff(ctx, false);
 397 }
 398 EXPORT_SYMBOL(drm_modeset_backoff);
 399
 400 /**
 401  * drm_modeset_backoff_interruptible - deadlock avoidance backoff
 402  * @ctx: the acquire context
 403  *
 404  * Interruptible version of drm_modeset_backoff()
 405  */
 406 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
 407 {
 408         return modeset_backoff(ctx, true);
 409 }
 410 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
 411
 412 /**
 413  * drm_modeset_lock - take modeset lock
 414  * @lock: lock to take
 415  * @ctx: acquire ctx
 416  *
 417  * If ctx is not NULL, then its ww acquire context is used and the
 418  * lock will be tracked by the context and can be released by calling
 419  * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
 420  * deadlock scenario has been detected and it is an error to attempt
 421  * to take any more locks without first calling drm_modeset_backoff().
 422  */
 423 int drm_modeset_lock(struct drm_modeset_lock *lock,
 424                 struct drm_modeset_acquire_ctx *ctx)
 425 {
 426         if (ctx)
 427                 return modeset_lock(lock, ctx, false, false);
 428
 429         ww_mutex_lock(&lock->mutex, NULL);
 430         return 0;
 431 }
 432 EXPORT_SYMBOL(drm_modeset_lock);
 433
 434 /**
 435  * drm_modeset_lock_interruptible - take modeset lock
 436  * @lock: lock to take
 437  * @ctx: acquire ctx
 438  *
 439  * Interruptible version of drm_modeset_lock()
 440  */
 441 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
 442                 struct drm_modeset_acquire_ctx *ctx)
 443 {
 444         if (ctx)
 445                 return modeset_lock(lock, ctx, true, false);
 446
 447         return ww_mutex_lock_interruptible(&lock->mutex, NULL);
 448 }
 449 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
 450
 451 /**
 452  * drm_modeset_unlock - drop modeset lock
 453  * @lock: lock to release
 454  */
 455 void drm_modeset_unlock(struct drm_modeset_lock *lock)
 456 {
 457         list_del_init(&lock->head);
 458         ww_mutex_unlock(&lock->mutex);
 459 }
 460 EXPORT_SYMBOL(drm_modeset_unlock);
 461
 462 /* In some legacy codepaths it's convenient to just grab all the crtc and plane
 463  * related locks. */
 464 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
 465                 struct drm_modeset_acquire_ctx *ctx)
 466 {
 467         struct drm_mode_config *config = &dev->mode_config;
 468         struct drm_crtc *crtc;
 469         struct drm_plane *plane;
 470         int ret = 0;
 471
 472         list_for_each_entry(crtc, &config->crtc_list, head) {
 473                 ret = drm_modeset_lock(&crtc->mutex, ctx);
 474                 if (ret)
 475                         return ret;
 476         }
 477
 478         list_for_each_entry(plane, &config->plane_list, head) {
 479                 ret = drm_modeset_lock(&plane->mutex, ctx);
 480                 if (ret)
 481                         return ret;
 482         }
 483
 484         return 0;
 485 }
 486 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);