2 * Copyright (C) 2014 Red Hat
3 * Author: Rob Clark <robdclark@gmail.com>
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:
12 * The above copyright notice and this permission notice shall be included in
13 * all copies or substantial portions of the Software.
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.
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);
54 * drm_modeset_drop_locks(&ctx);
55 * drm_modeset_acquire_fini(&ctx);
60 * __drm_modeset_lock_all - internal helper to grab all modeset locks
62 * @trylock: trylock mode for atomic contexts
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.
68 * 0 on success or negative error code on failure.
70 int __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),
78 trylock ? GFP_ATOMIC : GFP_KERNEL);
83 if (!mutex_trylock(&config->mutex))
86 mutex_lock(&config->mutex);
89 drm_modeset_acquire_init(ctx, 0);
90 ctx->trylock_only = trylock;
93 ret = drm_modeset_lock(&config->connection_mutex, ctx);
96 ret = drm_modeset_lock_all_crtcs(dev, ctx);
100 WARN_ON(config->acquire_ctx);
102 /* now we hold the locks, so now that it is safe, stash the
103 * ctx for drm_modeset_unlock_all():
105 config->acquire_ctx = ctx;
107 drm_warn_on_modeset_not_all_locked(dev);
112 if (ret == -EDEADLK) {
113 drm_modeset_backoff(ctx);
119 EXPORT_SYMBOL(__drm_modeset_lock_all);
122 * drm_modeset_lock_all - take all modeset locks
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.
129 void drm_modeset_lock_all(struct drm_device *dev)
131 WARN_ON(__drm_modeset_lock_all(dev, false) != 0);
133 EXPORT_SYMBOL(drm_modeset_lock_all);
136 * drm_modeset_unlock_all - drop all modeset locks
139 * This function drop all modeset locks taken by drm_modeset_lock_all.
141 void drm_modeset_unlock_all(struct drm_device *dev)
143 struct drm_mode_config *config = &dev->mode_config;
144 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
149 config->acquire_ctx = NULL;
150 drm_modeset_drop_locks(ctx);
151 drm_modeset_acquire_fini(ctx);
155 mutex_unlock(&dev->mode_config.mutex);
157 EXPORT_SYMBOL(drm_modeset_unlock_all);
160 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
162 * @plane: DRM plane to be updated on @crtc
164 * This function locks the given crtc and plane (which should be either the
165 * primary or cursor plane) using a hidden acquire context. This is necessary so
166 * that drivers internally using the atomic interfaces can grab further locks
167 * with the lock acquire context.
169 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
170 * converted to universal planes yet.
172 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
173 struct drm_plane *plane)
175 struct drm_modeset_acquire_ctx *ctx;
178 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
182 drm_modeset_acquire_init(ctx, 0);
185 ret = drm_modeset_lock(&crtc->mutex, ctx);
190 ret = drm_modeset_lock(&plane->mutex, ctx);
195 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
201 WARN_ON(crtc->acquire_ctx);
203 /* now we hold the locks, so now that it is safe, stash the
204 * ctx for drm_modeset_unlock_crtc():
206 crtc->acquire_ctx = ctx;
211 if (ret == -EDEADLK) {
212 drm_modeset_backoff(ctx);
216 EXPORT_SYMBOL(drm_modeset_lock_crtc);
219 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
222 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
223 * locking, and store the acquire ctx in the corresponding crtc. All other
224 * legacy operations take all locks and use a global acquire context. This
225 * function grabs the right one.
227 struct drm_modeset_acquire_ctx *
228 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
230 if (crtc->acquire_ctx)
231 return crtc->acquire_ctx;
233 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
235 return crtc->dev->mode_config.acquire_ctx;
237 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
240 * drm_modeset_unlock_crtc - drop crtc lock
243 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
244 * locks acquired through the hidden context.
246 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
248 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
253 crtc->acquire_ctx = NULL;
254 drm_modeset_drop_locks(ctx);
255 drm_modeset_acquire_fini(ctx);
259 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
262 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
265 * Useful as a debug assert.
267 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
269 struct drm_crtc *crtc;
271 /* Locking is currently fubar in the panic handler. */
272 if (oops_in_progress)
275 list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
276 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
278 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
279 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
281 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
284 * drm_modeset_acquire_init - initialize acquire context
285 * @ctx: the acquire context
288 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
291 memset(ctx, 0, sizeof(*ctx));
292 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
293 INIT_LIST_HEAD(&ctx->locked);
295 EXPORT_SYMBOL(drm_modeset_acquire_init);
298 * drm_modeset_acquire_fini - cleanup acquire context
299 * @ctx: the acquire context
301 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
303 ww_acquire_fini(&ctx->ww_ctx);
305 EXPORT_SYMBOL(drm_modeset_acquire_fini);
308 * drm_modeset_drop_locks - drop all locks
309 * @ctx: the acquire context
311 * Drop all locks currently held against this acquire context.
313 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
315 WARN_ON(ctx->contended);
316 while (!list_empty(&ctx->locked)) {
317 struct drm_modeset_lock *lock;
319 lock = list_first_entry(&ctx->locked,
320 struct drm_modeset_lock, head);
322 drm_modeset_unlock(lock);
325 EXPORT_SYMBOL(drm_modeset_drop_locks);
327 static inline int modeset_lock(struct drm_modeset_lock *lock,
328 struct drm_modeset_acquire_ctx *ctx,
329 bool interruptible, bool slow)
333 WARN_ON(ctx->contended);
335 if (ctx->trylock_only) {
336 if (!ww_mutex_trylock(&lock->mutex))
340 } else if (interruptible && slow) {
341 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
342 } else if (interruptible) {
343 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
345 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
348 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
351 WARN_ON(!list_empty(&lock->head));
352 list_add(&lock->head, &ctx->locked);
353 } else if (ret == -EALREADY) {
354 /* we already hold the lock.. this is fine. For atomic
355 * we will need to be able to drm_modeset_lock() things
356 * without having to keep track of what is already locked
360 } else if (ret == -EDEADLK) {
361 ctx->contended = lock;
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 list_del_init(&lock->head);
454 ww_mutex_unlock(&lock->mutex);
456 EXPORT_SYMBOL(drm_modeset_unlock);
458 /* In some legacy codepaths it's convenient to just grab all the crtc and plane
460 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
461 struct drm_modeset_acquire_ctx *ctx)
463 struct drm_mode_config *config = &dev->mode_config;
464 struct drm_crtc *crtc;
465 struct drm_plane *plane;
468 list_for_each_entry(crtc, &config->crtc_list, head) {
469 ret = drm_modeset_lock(&crtc->mutex, ctx);
474 list_for_each_entry(plane, &config->plane_list, head) {
475 ret = drm_modeset_lock(&plane->mutex, ctx);
482 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);