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