2 * Copyright (C) 2014 Red Hat
3 * Author: Rob Clark <robdclark@gmail.com>
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6 * copy of this software and associated documentation files (the "Software"),
7 * to deal in the Software without restriction, including without limitation
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12 * The above copyright notice and this permission notice shall be included in
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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
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25 #include <drm/drm_crtc.h>
26 #include <drm/drm_modeset_lock.h>
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.
38 * For basic principles of ww_mutex, see: Documentation/locking/ww-mutex-design.txt
40 * The basic usage pattern is to:
42 * drm_modeset_acquire_init(&ctx)
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);
52 * drm_modeset_drop_locks(&ctx);
53 * drm_modeset_acquire_fini(&ctx);
57 * drm_modeset_lock_all - take all modeset locks
60 * This function takes all modeset locks, suitable where a more fine-grained
61 * scheme isn't (yet) implemented. Locks must be dropped by calling the
62 * drm_modeset_unlock_all() function.
64 * This function is deprecated. It allocates a lock acquisition context and
65 * stores it in the DRM device's ->mode_config. This facilitate conversion of
66 * existing code because it removes the need to manually deal with the
67 * acquisition context, but it is also brittle because the context is global
68 * and care must be taken not to nest calls. New code should use the
69 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
71 void drm_modeset_lock_all(struct drm_device *dev)
73 struct drm_mode_config *config = &dev->mode_config;
74 struct drm_modeset_acquire_ctx *ctx;
77 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
81 mutex_lock(&config->mutex);
83 drm_modeset_acquire_init(ctx, 0);
86 ret = drm_modeset_lock_all_ctx(dev, ctx);
88 if (ret == -EDEADLK) {
89 drm_modeset_backoff(ctx);
93 drm_modeset_acquire_fini(ctx);
98 WARN_ON(config->acquire_ctx);
101 * We hold the locks now, so it is safe to stash the acquisition
102 * context for drm_modeset_unlock_all().
104 config->acquire_ctx = ctx;
106 drm_warn_on_modeset_not_all_locked(dev);
108 EXPORT_SYMBOL(drm_modeset_lock_all);
111 * drm_modeset_unlock_all - drop all modeset locks
114 * This function drops all modeset locks taken by a previous call to the
115 * drm_modeset_lock_all() function.
117 * This function is deprecated. It uses the lock acquisition context stored
118 * in the DRM device's ->mode_config. This facilitates conversion of existing
119 * code because it removes the need to manually deal with the acquisition
120 * context, but it is also brittle because the context is global and care must
121 * be taken not to nest calls. New code should pass the acquisition context
122 * directly to the drm_modeset_drop_locks() function.
124 void drm_modeset_unlock_all(struct drm_device *dev)
126 struct drm_mode_config *config = &dev->mode_config;
127 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
132 config->acquire_ctx = NULL;
133 drm_modeset_drop_locks(ctx);
134 drm_modeset_acquire_fini(ctx);
138 mutex_unlock(&dev->mode_config.mutex);
140 EXPORT_SYMBOL(drm_modeset_unlock_all);
143 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
145 * @plane: DRM plane to be updated on @crtc
147 * This function locks the given crtc and plane (which should be either the
148 * primary or cursor plane) using a hidden acquire context. This is necessary so
149 * that drivers internally using the atomic interfaces can grab further locks
150 * with the lock acquire context.
152 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
153 * converted to universal planes yet.
155 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
156 struct drm_plane *plane)
158 struct drm_modeset_acquire_ctx *ctx;
161 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
165 drm_modeset_acquire_init(ctx, 0);
168 ret = drm_modeset_lock(&crtc->mutex, ctx);
173 ret = drm_modeset_lock(&plane->mutex, ctx);
178 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
184 WARN_ON(crtc->acquire_ctx);
186 /* now we hold the locks, so now that it is safe, stash the
187 * ctx for drm_modeset_unlock_crtc():
189 crtc->acquire_ctx = ctx;
194 if (ret == -EDEADLK) {
195 drm_modeset_backoff(ctx);
199 EXPORT_SYMBOL(drm_modeset_lock_crtc);
202 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
205 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
206 * locking, and store the acquire ctx in the corresponding crtc. All other
207 * legacy operations take all locks and use a global acquire context. This
208 * function grabs the right one.
210 struct drm_modeset_acquire_ctx *
211 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
213 if (crtc->acquire_ctx)
214 return crtc->acquire_ctx;
216 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
218 return crtc->dev->mode_config.acquire_ctx;
220 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
223 * drm_modeset_unlock_crtc - drop crtc lock
226 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
227 * locks acquired through the hidden context.
229 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
231 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
236 crtc->acquire_ctx = NULL;
237 drm_modeset_drop_locks(ctx);
238 drm_modeset_acquire_fini(ctx);
242 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
245 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
248 * Useful as a debug assert.
250 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
252 struct drm_crtc *crtc;
254 /* Locking is currently fubar in the panic handler. */
259 if (oops_in_progress)
263 drm_for_each_crtc(crtc, dev)
264 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
266 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
267 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
269 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
272 * drm_modeset_acquire_init - initialize acquire context
273 * @ctx: the acquire context
276 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
279 memset(ctx, 0, sizeof(*ctx));
280 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
281 INIT_LIST_HEAD(&ctx->locked);
283 EXPORT_SYMBOL(drm_modeset_acquire_init);
286 * drm_modeset_acquire_fini - cleanup acquire context
287 * @ctx: the acquire context
289 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
291 ww_acquire_fini(&ctx->ww_ctx);
293 EXPORT_SYMBOL(drm_modeset_acquire_fini);
296 * drm_modeset_drop_locks - drop all locks
297 * @ctx: the acquire context
299 * Drop all locks currently held against this acquire context.
301 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
303 WARN_ON(ctx->contended);
304 while (!list_empty(&ctx->locked)) {
305 struct drm_modeset_lock_info *info;
307 info = list_first_entry(&ctx->locked,
308 struct drm_modeset_lock_info, ctx_entry);
310 drm_modeset_unlock(info->lock);
313 EXPORT_SYMBOL(drm_modeset_drop_locks);
315 static inline int modeset_lock(struct drm_modeset_lock *lock,
316 struct drm_modeset_acquire_ctx *ctx,
317 bool interruptible, bool slow)
321 WARN_ON(ctx->contended);
323 if (ctx->trylock_only) {
325 lockdep_assert_held(&ctx->ww_ctx);
328 if (!ww_mutex_trylock(&lock->mutex))
332 } else if (interruptible && slow) {
333 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
334 } else if (interruptible) {
335 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
337 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
340 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
342 if (ret == -EALREADY) {
343 /* we already hold the lock.. this is fine. For atomic
344 * we will need to be able to drm_modeset_lock() things
345 * without having to keep track of what is already locked
349 } else if (ret == -EDEADLK) {
350 ctx->contended = lock;
353 struct drm_modeset_lock_info *info;
355 info = kzalloc(sizeof(*info), GFP_KERNEL);
356 INIT_LIST_HEAD(&info->ctx_entry);
357 INIT_LIST_HEAD(&info->lock_entry);
360 list_add(&info->ctx_entry, &ctx->locked);
361 list_add(&info->lock_entry, &lock->locked);
367 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
370 struct drm_modeset_lock *contended = ctx->contended;
372 ctx->contended = NULL;
374 if (WARN_ON(!contended))
377 drm_modeset_drop_locks(ctx);
379 return modeset_lock(contended, ctx, interruptible, true);
383 * drm_modeset_backoff - deadlock avoidance backoff
384 * @ctx: the acquire context
386 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
387 * you must call this function to drop all currently held locks and
388 * block until the contended lock becomes available.
390 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
392 modeset_backoff(ctx, false);
394 EXPORT_SYMBOL(drm_modeset_backoff);
397 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
398 * @ctx: the acquire context
400 * Interruptible version of drm_modeset_backoff()
402 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
404 return modeset_backoff(ctx, true);
406 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
409 * drm_modeset_lock - take modeset lock
410 * @lock: lock to take
413 * If ctx is not NULL, then its ww acquire context is used and the
414 * lock will be tracked by the context and can be released by calling
415 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
416 * deadlock scenario has been detected and it is an error to attempt
417 * to take any more locks without first calling drm_modeset_backoff().
419 int drm_modeset_lock(struct drm_modeset_lock *lock,
420 struct drm_modeset_acquire_ctx *ctx)
423 return modeset_lock(lock, ctx, false, false);
425 ww_mutex_lock(&lock->mutex, NULL);
428 EXPORT_SYMBOL(drm_modeset_lock);
431 * drm_modeset_lock_interruptible - take modeset lock
432 * @lock: lock to take
435 * Interruptible version of drm_modeset_lock()
437 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
438 struct drm_modeset_acquire_ctx *ctx)
441 return modeset_lock(lock, ctx, true, false);
443 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
445 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
448 * drm_modeset_unlock - drop modeset lock
449 * @lock: lock to release
451 void drm_modeset_unlock(struct drm_modeset_lock *lock)
453 struct drm_modeset_lock_info *info;
455 /* undo in reverse order */
456 if (!list_empty(&lock->locked)) {
457 info = list_last_entry(&lock->locked,
458 struct drm_modeset_lock_info, lock_entry);
459 list_del_init(&info->lock_entry);
461 list_del_init(&info->ctx_entry);
464 ww_mutex_unlock(&lock->mutex);
466 EXPORT_SYMBOL(drm_modeset_unlock);
469 * drm_modeset_lock_all_ctx - take all modeset locks
471 * @ctx: lock acquisition context
473 * This function takes all modeset locks, suitable where a more fine-grained
474 * scheme isn't (yet) implemented.
476 * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
477 * since that lock isn't required for modeset state changes. Callers which
478 * need to grab that lock too need to do so outside of the acquire context
481 * Locks acquired with this function should be released by calling the
482 * drm_modeset_drop_locks() function on @ctx.
484 * Returns: 0 on success or a negative error-code on failure.
486 int drm_modeset_lock_all_ctx(struct drm_device *dev,
487 struct drm_modeset_acquire_ctx *ctx)
489 struct drm_crtc *crtc;
490 struct drm_plane *plane;
493 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
497 drm_for_each_crtc(crtc, dev) {
498 ret = drm_modeset_lock(&crtc->mutex, ctx);
503 drm_for_each_plane(plane, dev) {
504 ret = drm_modeset_lock(&plane->mutex, ctx);
511 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);