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