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