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
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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)) {
88 mutex_lock(&config->mutex);
91 drm_modeset_acquire_init(ctx, 0);
92 ctx->trylock_only = trylock;
95 ret = drm_modeset_lock(&config->connection_mutex, ctx);
98 ret = drm_modeset_lock_all_crtcs(dev, ctx);
102 WARN_ON(config->acquire_ctx);
104 /* now we hold the locks, so now that it is safe, stash the
105 * ctx for drm_modeset_unlock_all():
107 config->acquire_ctx = ctx;
109 drm_warn_on_modeset_not_all_locked(dev);
114 if (ret == -EDEADLK) {
115 drm_modeset_backoff(ctx);
123 EXPORT_SYMBOL(__drm_modeset_lock_all);
126 * drm_modeset_lock_all - take all modeset locks
129 * This function takes all modeset locks, suitable where a more fine-grained
130 * scheme isn't (yet) implemented. Locks must be dropped with
131 * drm_modeset_unlock_all.
133 void drm_modeset_lock_all(struct drm_device *dev)
135 WARN_ON(__drm_modeset_lock_all(dev, false) != 0);
137 EXPORT_SYMBOL(drm_modeset_lock_all);
140 * drm_modeset_unlock_all - drop all modeset locks
143 * This function drop all modeset locks taken by drm_modeset_lock_all.
145 void drm_modeset_unlock_all(struct drm_device *dev)
147 struct drm_mode_config *config = &dev->mode_config;
148 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
153 config->acquire_ctx = NULL;
154 drm_modeset_drop_locks(ctx);
155 drm_modeset_acquire_fini(ctx);
159 mutex_unlock(&dev->mode_config.mutex);
161 EXPORT_SYMBOL(drm_modeset_unlock_all);
164 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
166 * @plane: DRM plane to be updated on @crtc
168 * This function locks the given crtc and plane (which should be either the
169 * primary or cursor plane) using a hidden acquire context. This is necessary so
170 * that drivers internally using the atomic interfaces can grab further locks
171 * with the lock acquire context.
173 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
174 * converted to universal planes yet.
176 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
177 struct drm_plane *plane)
179 struct drm_modeset_acquire_ctx *ctx;
182 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
186 drm_modeset_acquire_init(ctx, 0);
189 ret = drm_modeset_lock(&crtc->mutex, ctx);
194 ret = drm_modeset_lock(&plane->mutex, ctx);
199 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
205 WARN_ON(crtc->acquire_ctx);
207 /* now we hold the locks, so now that it is safe, stash the
208 * ctx for drm_modeset_unlock_crtc():
210 crtc->acquire_ctx = ctx;
215 if (ret == -EDEADLK) {
216 drm_modeset_backoff(ctx);
220 EXPORT_SYMBOL(drm_modeset_lock_crtc);
223 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
226 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
227 * locking, and store the acquire ctx in the corresponding crtc. All other
228 * legacy operations take all locks and use a global acquire context. This
229 * function grabs the right one.
231 struct drm_modeset_acquire_ctx *
232 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
234 if (crtc->acquire_ctx)
235 return crtc->acquire_ctx;
237 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
239 return crtc->dev->mode_config.acquire_ctx;
241 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
244 * drm_modeset_unlock_crtc - drop crtc lock
247 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
248 * locks acquired through the hidden context.
250 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
252 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
257 crtc->acquire_ctx = NULL;
258 drm_modeset_drop_locks(ctx);
259 drm_modeset_acquire_fini(ctx);
263 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
266 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
269 * Useful as a debug assert.
271 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
273 struct drm_crtc *crtc;
275 /* Locking is currently fubar in the panic handler. */
277 if (oops_in_progress)
281 list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
282 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
284 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
285 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
287 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
290 * drm_modeset_acquire_init - initialize acquire context
291 * @ctx: the acquire context
294 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
297 memset(ctx, 0, sizeof(*ctx));
298 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
299 INIT_LIST_HEAD(&ctx->locked);
301 EXPORT_SYMBOL(drm_modeset_acquire_init);
304 * drm_modeset_acquire_fini - cleanup acquire context
305 * @ctx: the acquire context
307 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
309 ww_acquire_fini(&ctx->ww_ctx);
311 EXPORT_SYMBOL(drm_modeset_acquire_fini);
314 * drm_modeset_drop_locks - drop all locks
315 * @ctx: the acquire context
317 * Drop all locks currently held against this acquire context.
319 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
321 WARN_ON(ctx->contended);
322 while (!list_empty(&ctx->locked)) {
323 struct drm_modeset_lock_info *info;
325 info = list_first_entry(&ctx->locked,
326 struct drm_modeset_lock_info, ctx_entry);
328 drm_modeset_unlock(info->lock);
331 EXPORT_SYMBOL(drm_modeset_drop_locks);
333 static inline int modeset_lock(struct drm_modeset_lock *lock,
334 struct drm_modeset_acquire_ctx *ctx,
335 bool interruptible, bool slow)
339 WARN_ON(ctx->contended);
341 if (ctx->trylock_only) {
342 if (!ww_mutex_trylock(&lock->mutex))
346 } else if (interruptible && slow) {
347 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
348 } else if (interruptible) {
349 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
351 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
354 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
356 if (ret == -EALREADY) {
357 /* we already hold the lock.. this is fine. For atomic
358 * we will need to be able to drm_modeset_lock() things
359 * without having to keep track of what is already locked
363 } else if (ret == -EDEADLK) {
364 ctx->contended = lock;
367 struct drm_modeset_lock_info *info;
369 info = kzalloc(sizeof(*info), GFP_KERNEL);
370 INIT_LIST_HEAD(&info->ctx_entry);
371 INIT_LIST_HEAD(&info->lock_entry);
374 list_add(&info->ctx_entry, &ctx->locked);
375 list_add(&info->lock_entry, &lock->locked);
381 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
384 struct drm_modeset_lock *contended = ctx->contended;
386 ctx->contended = NULL;
388 if (WARN_ON(!contended))
391 drm_modeset_drop_locks(ctx);
393 return modeset_lock(contended, ctx, interruptible, true);
397 * drm_modeset_backoff - deadlock avoidance backoff
398 * @ctx: the acquire context
400 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
401 * you must call this function to drop all currently held locks and
402 * block until the contended lock becomes available.
404 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
406 modeset_backoff(ctx, false);
408 EXPORT_SYMBOL(drm_modeset_backoff);
411 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
412 * @ctx: the acquire context
414 * Interruptible version of drm_modeset_backoff()
416 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
418 return modeset_backoff(ctx, true);
420 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
423 * drm_modeset_lock - take modeset lock
424 * @lock: lock to take
427 * If ctx is not NULL, then its ww acquire context is used and the
428 * lock will be tracked by the context and can be released by calling
429 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
430 * deadlock scenario has been detected and it is an error to attempt
431 * to take any more locks without first calling drm_modeset_backoff().
433 int drm_modeset_lock(struct drm_modeset_lock *lock,
434 struct drm_modeset_acquire_ctx *ctx)
437 return modeset_lock(lock, ctx, false, false);
439 ww_mutex_lock(&lock->mutex, NULL);
442 EXPORT_SYMBOL(drm_modeset_lock);
445 * drm_modeset_lock_interruptible - take modeset lock
446 * @lock: lock to take
449 * Interruptible version of drm_modeset_lock()
451 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
452 struct drm_modeset_acquire_ctx *ctx)
455 return modeset_lock(lock, ctx, true, false);
457 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
459 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
462 * drm_modeset_unlock - drop modeset lock
463 * @lock: lock to release
465 void drm_modeset_unlock(struct drm_modeset_lock *lock)
467 struct drm_modeset_lock_info *info;
469 /* undo in reverse order */
470 if (!list_empty(&lock->locked)) {
471 info = list_last_entry(&lock->locked,
472 struct drm_modeset_lock_info, lock_entry);
473 list_del_init(&info->lock_entry);
475 list_del_init(&info->ctx_entry);
478 ww_mutex_unlock(&lock->mutex);
480 EXPORT_SYMBOL(drm_modeset_unlock);
482 /* In some legacy codepaths it's convenient to just grab all the crtc and plane
484 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
485 struct drm_modeset_acquire_ctx *ctx)
487 struct drm_mode_config *config = &dev->mode_config;
488 struct drm_crtc *crtc;
489 struct drm_plane *plane;
492 list_for_each_entry(crtc, &config->crtc_list, head) {
493 ret = drm_modeset_lock(&crtc->mutex, ctx);
498 list_for_each_entry(plane, &config->plane_list, head) {
499 ret = drm_modeset_lock(&plane->mutex, ctx);
506 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);