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  * drm_modeset_lock_all - take all modeset locks
  60  * @dev: DRM device
  61  *
  62  * This function takes all modeset locks, suitable where a more fine-grained
  63  * scheme isn't (yet) implemented. Locks must be dropped by calling the
  64  * drm_modeset_unlock_all() function.
  65  *
  66  * This function is deprecated. It allocates a lock acquisition context and
  67  * stores it in the DRM device's ->mode_config. This facilitate conversion of
  68  * existing code because it removes the need to manually deal with the
  69  * acquisition context, but it is also brittle because the context is global
  70  * and care must be taken not to nest calls. New code should use the
  71  * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
  72  */
  73 void drm_modeset_lock_all(struct drm_device *dev)
  74 {
  75         struct drm_mode_config *config = &dev->mode_config;
  76         struct drm_modeset_acquire_ctx *ctx;
  77         int ret;
  78
  79         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
  80         if (WARN_ON(!ctx))
  81                 return;
  82
  83         mutex_lock(&config->mutex);
  84
  85         drm_modeset_acquire_init(ctx, 0);
  86
  87 retry:
  88         ret = drm_modeset_lock_all_ctx(dev, ctx);
  89         if (ret < 0) {
  90                 if (ret == -EDEADLK) {
  91                         drm_modeset_backoff(ctx);
  92                         goto retry;
  93                 }
  94
  95                 drm_modeset_acquire_fini(ctx);
  96                 kfree(ctx);
  97                 return;
  98         }
  99
 100         WARN_ON(config->acquire_ctx);
 101
 102         /*
 103          * We hold the locks now, so it is safe to stash the acquisition
 104          * context for drm_modeset_unlock_all().
 105          */
 106         config->acquire_ctx = ctx;
 107
 108         drm_warn_on_modeset_not_all_locked(dev);
 109 }
 110 EXPORT_SYMBOL(drm_modeset_lock_all);
 111
 112 /**
 113  * drm_modeset_unlock_all - drop all modeset locks
 114  * @dev: DRM device
 115  *
 116  * This function drops all modeset locks taken by a previous call to the
 117  * drm_modeset_lock_all() function.
 118  *
 119  * This function is deprecated. It uses the lock acquisition context stored
 120  * in the DRM device's ->mode_config. This facilitates conversion of existing
 121  * code because it removes the need to manually deal with the acquisition
 122  * context, but it is also brittle because the context is global and care must
 123  * be taken not to nest calls. New code should pass the acquisition context
 124  * directly to the drm_modeset_drop_locks() function.
 125  */
 126 void drm_modeset_unlock_all(struct drm_device *dev)
 127 {
 128         struct drm_mode_config *config = &dev->mode_config;
 129         struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
 130
 131         if (WARN_ON(!ctx))
 132                 return;
 133
 134         config->acquire_ctx = NULL;
 135         drm_modeset_drop_locks(ctx);
 136         drm_modeset_acquire_fini(ctx);
 137
 138         kfree(ctx);
 139
 140         mutex_unlock(&dev->mode_config.mutex);
 141 }
 142 EXPORT_SYMBOL(drm_modeset_unlock_all);
 143
 144 /**
 145  * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
 146  * @crtc: DRM CRTC
 147  * @plane: DRM plane to be updated on @crtc
 148  *
 149  * This function locks the given crtc and plane (which should be either the
 150  * primary or cursor plane) using a hidden acquire context. This is necessary so
 151  * that drivers internally using the atomic interfaces can grab further locks
 152  * with the lock acquire context.
 153  *
 154  * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
 155  * converted to universal planes yet.
 156  */
 157 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
 158                            struct drm_plane *plane)
 159 {
 160         struct drm_modeset_acquire_ctx *ctx;
 161         int ret;
 162
 163         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 164         if (WARN_ON(!ctx))
 165                 return;
 166
 167         drm_modeset_acquire_init(ctx, 0);
 168
 169 retry:
 170         ret = drm_modeset_lock(&crtc->mutex, ctx);
 171         if (ret)
 172                 goto fail;
 173
 174         if (plane) {
 175                 ret = drm_modeset_lock(&plane->mutex, ctx);
 176                 if (ret)
 177                         goto fail;
 178
 179                 if (plane->crtc) {
 180                         ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
 181                         if (ret)
 182                                 goto fail;
 183                 }
 184         }
 185
 186         WARN_ON(crtc->acquire_ctx);
 187
 188         /* now we hold the locks, so now that it is safe, stash the
 189          * ctx for drm_modeset_unlock_crtc():
 190          */
 191         crtc->acquire_ctx = ctx;
 192
 193         return;
 194
 195 fail:
 196         if (ret == -EDEADLK) {
 197                 drm_modeset_backoff(ctx);
 198                 goto retry;
 199         }
 200 }
 201 EXPORT_SYMBOL(drm_modeset_lock_crtc);
 202
 203 /**
 204  * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
 205  * @crtc: drm crtc
 206  *
 207  * Legacy ioctl operations like cursor updates or page flips only have per-crtc
 208  * locking, and store the acquire ctx in the corresponding crtc. All other
 209  * legacy operations take all locks and use a global acquire context. This
 210  * function grabs the right one.
 211  */
 212 struct drm_modeset_acquire_ctx *
 213 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
 214 {
 215         if (crtc->acquire_ctx)
 216                 return crtc->acquire_ctx;
 217
 218         WARN_ON(!crtc->dev->mode_config.acquire_ctx);
 219
 220         return crtc->dev->mode_config.acquire_ctx;
 221 }
 222 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
 223
 224 /**
 225  * drm_modeset_unlock_crtc - drop crtc lock
 226  * @crtc: drm crtc
 227  *
 228  * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
 229  * locks acquired through the hidden context.
 230  */
 231 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
 232 {
 233         struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
 234
 235         if (WARN_ON(!ctx))
 236                 return;
 237
 238         crtc->acquire_ctx = NULL;
 239         drm_modeset_drop_locks(ctx);
 240         drm_modeset_acquire_fini(ctx);
 241
 242         kfree(ctx);
 243 }
 244 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
 245
 246 /**
 247  * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
 248  * @dev: device
 249  *
 250  * Useful as a debug assert.
 251  */
 252 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
 253 {
 254         struct drm_crtc *crtc;
 255
 256         /* Locking is currently fubar in the panic handler. */
 257         if (oops_in_progress)
 258                 return;
 259
 260         drm_for_each_crtc(crtc, dev)
 261                 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
 262
 263         WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
 264         WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
 265 }
 266 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
 267
 268 /**
 269  * drm_modeset_acquire_init - initialize acquire context
 270  * @ctx: the acquire context
 271  * @flags: for future
 272  */
 273 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 274                 uint32_t flags)
 275 {
 276         memset(ctx, 0, sizeof(*ctx));
 277         ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
 278         INIT_LIST_HEAD(&ctx->locked);
 279 }
 280 EXPORT_SYMBOL(drm_modeset_acquire_init);
 281
 282 /**
 283  * drm_modeset_acquire_fini - cleanup acquire context
 284  * @ctx: the acquire context
 285  */
 286 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
 287 {
 288         ww_acquire_fini(&ctx->ww_ctx);
 289 }
 290 EXPORT_SYMBOL(drm_modeset_acquire_fini);
 291
 292 /**
 293  * drm_modeset_drop_locks - drop all locks
 294  * @ctx: the acquire context
 295  *
 296  * Drop all locks currently held against this acquire context.
 297  */
 298 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
 299 {
 300         WARN_ON(ctx->contended);
 301         while (!list_empty(&ctx->locked)) {
 302                 struct drm_modeset_lock *lock;
 303
 304                 lock = list_first_entry(&ctx->locked,
 305                                 struct drm_modeset_lock, head);
 306
 307                 drm_modeset_unlock(lock);
 308         }
 309 }
 310 EXPORT_SYMBOL(drm_modeset_drop_locks);
 311
 312 static inline int modeset_lock(struct drm_modeset_lock *lock,
 313                 struct drm_modeset_acquire_ctx *ctx,
 314                 bool interruptible, bool slow)
 315 {
 316         int ret;
 317
 318         WARN_ON(ctx->contended);
 319
 320         if (ctx->trylock_only) {
 321                 lockdep_assert_held(&ctx->ww_ctx);
 322
 323                 if (!ww_mutex_trylock(&lock->mutex))
 324                         return -EBUSY;
 325                 else
 326                         return 0;
 327         } else if (interruptible && slow) {
 328                 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
 329         } else if (interruptible) {
 330                 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
 331         } else if (slow) {
 332                 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
 333                 ret = 0;
 334         } else {
 335                 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
 336         }
 337         if (!ret) {
 338                 WARN_ON(!list_empty(&lock->head));
 339                 list_add(&lock->head, &ctx->locked);
 340         } else if (ret == -EALREADY) {
 341                 /* we already hold the lock.. this is fine.  For atomic
 342                  * we will need to be able to drm_modeset_lock() things
 343                  * without having to keep track of what is already locked
 344                  * or not.
 345                  */
 346                 ret = 0;
 347         } else if (ret == -EDEADLK) {
 348                 ctx->contended = lock;
 349         }
 350
 351         return ret;
 352 }
 353
 354 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
 355                 bool interruptible)
 356 {
 357         struct drm_modeset_lock *contended = ctx->contended;
 358
 359         ctx->contended = NULL;
 360
 361         if (WARN_ON(!contended))
 362                 return 0;
 363
 364         drm_modeset_drop_locks(ctx);
 365
 366         return modeset_lock(contended, ctx, interruptible, true);
 367 }
 368
 369 /**
 370  * drm_modeset_backoff - deadlock avoidance backoff
 371  * @ctx: the acquire context
 372  *
 373  * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
 374  * you must call this function to drop all currently held locks and
 375  * block until the contended lock becomes available.
 376  */
 377 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
 378 {
 379         modeset_backoff(ctx, false);
 380 }
 381 EXPORT_SYMBOL(drm_modeset_backoff);
 382
 383 /**
 384  * drm_modeset_backoff_interruptible - deadlock avoidance backoff
 385  * @ctx: the acquire context
 386  *
 387  * Interruptible version of drm_modeset_backoff()
 388  */
 389 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
 390 {
 391         return modeset_backoff(ctx, true);
 392 }
 393 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
 394
 395 /**
 396  * drm_modeset_lock - take modeset lock
 397  * @lock: lock to take
 398  * @ctx: acquire ctx
 399  *
 400  * If ctx is not NULL, then its ww acquire context is used and the
 401  * lock will be tracked by the context and can be released by calling
 402  * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
 403  * deadlock scenario has been detected and it is an error to attempt
 404  * to take any more locks without first calling drm_modeset_backoff().
 405  */
 406 int drm_modeset_lock(struct drm_modeset_lock *lock,
 407                 struct drm_modeset_acquire_ctx *ctx)
 408 {
 409         if (ctx)
 410                 return modeset_lock(lock, ctx, false, false);
 411
 412         ww_mutex_lock(&lock->mutex, NULL);
 413         return 0;
 414 }
 415 EXPORT_SYMBOL(drm_modeset_lock);
 416
 417 /**
 418  * drm_modeset_lock_interruptible - take modeset lock
 419  * @lock: lock to take
 420  * @ctx: acquire ctx
 421  *
 422  * Interruptible version of drm_modeset_lock()
 423  */
 424 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
 425                 struct drm_modeset_acquire_ctx *ctx)
 426 {
 427         if (ctx)
 428                 return modeset_lock(lock, ctx, true, false);
 429
 430         return ww_mutex_lock_interruptible(&lock->mutex, NULL);
 431 }
 432 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
 433
 434 /**
 435  * drm_modeset_unlock - drop modeset lock
 436  * @lock: lock to release
 437  */
 438 void drm_modeset_unlock(struct drm_modeset_lock *lock)
 439 {
 440         list_del_init(&lock->head);
 441         ww_mutex_unlock(&lock->mutex);
 442 }
 443 EXPORT_SYMBOL(drm_modeset_unlock);
 444
 445 /**
 446  * drm_modeset_lock_all_ctx - take all modeset locks
 447  * @dev: DRM device
 448  * @ctx: lock acquisition context
 449  *
 450  * This function takes all modeset locks, suitable where a more fine-grained
 451  * scheme isn't (yet) implemented.
 452  *
 453  * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
 454  * since that lock isn't required for modeset state changes. Callers which
 455  * need to grab that lock too need to do so outside of the acquire context
 456  * @ctx.
 457  *
 458  * Locks acquired with this function should be released by calling the
 459  * drm_modeset_drop_locks() function on @ctx.
 460  *
 461  * Returns: 0 on success or a negative error-code on failure.
 462  */
 463 int drm_modeset_lock_all_ctx(struct drm_device *dev,
 464                              struct drm_modeset_acquire_ctx *ctx)
 465 {
 466         struct drm_crtc *crtc;
 467         struct drm_plane *plane;
 468         int ret;
 469
 470         ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
 471         if (ret)
 472                 return ret;
 473
 474         drm_for_each_crtc(crtc, dev) {
 475                 ret = drm_modeset_lock(&crtc->mutex, ctx);
 476                 if (ret)
 477                         return ret;
 478         }
 479
 480         drm_for_each_plane(plane, dev) {
 481                 ret = drm_modeset_lock(&plane->mutex, ctx);
 482                 if (ret)
 483                         return ret;
 484         }
 485
 486         return 0;
 487 }
 488 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);