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);
59 * drm_modeset_lock_all - take all modeset locks
62 * This function takes all modeset locks, suitable where a more fine-grained
63 * scheme isn't (yet) implemented. Locks must be dropped with
64 * drm_modeset_unlock_all.
66 void drm_modeset_lock_all(struct drm_device *dev)
68 struct drm_mode_config *config = &dev->mode_config;
69 struct drm_modeset_acquire_ctx *ctx;
72 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
76 mutex_lock(&config->mutex);
78 drm_modeset_acquire_init(ctx, 0);
81 ret = drm_modeset_lock(&config->connection_mutex, ctx);
84 ret = drm_modeset_lock_all_crtcs(dev, ctx);
88 WARN_ON(config->acquire_ctx);
90 /* now we hold the locks, so now that it is safe, stash the
91 * ctx for drm_modeset_unlock_all():
93 config->acquire_ctx = ctx;
95 drm_warn_on_modeset_not_all_locked(dev);
100 if (ret == -EDEADLK) {
101 drm_modeset_backoff(ctx);
107 EXPORT_SYMBOL(drm_modeset_lock_all);
110 * drm_modeset_unlock_all - drop all modeset locks
113 * This function drop all modeset locks taken by drm_modeset_lock_all.
115 void drm_modeset_unlock_all(struct drm_device *dev)
117 struct drm_mode_config *config = &dev->mode_config;
118 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
123 config->acquire_ctx = NULL;
124 drm_modeset_drop_locks(ctx);
125 drm_modeset_acquire_fini(ctx);
129 mutex_unlock(&dev->mode_config.mutex);
131 EXPORT_SYMBOL(drm_modeset_unlock_all);
134 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
136 * @plane: DRM plane to be updated on @crtc
138 * This function locks the given crtc and plane (which should be either the
139 * primary or cursor plane) using a hidden acquire context. This is necessary so
140 * that drivers internally using the atomic interfaces can grab further locks
141 * with the lock acquire context.
143 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
144 * converted to universal planes yet.
146 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
147 struct drm_plane *plane)
149 struct drm_modeset_acquire_ctx *ctx;
152 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
156 drm_modeset_acquire_init(ctx, 0);
159 ret = drm_modeset_lock(&crtc->mutex, ctx);
164 ret = drm_modeset_lock(&plane->mutex, ctx);
169 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
175 WARN_ON(crtc->acquire_ctx);
177 /* now we hold the locks, so now that it is safe, stash the
178 * ctx for drm_modeset_unlock_crtc():
180 crtc->acquire_ctx = ctx;
185 if (ret == -EDEADLK) {
186 drm_modeset_backoff(ctx);
190 EXPORT_SYMBOL(drm_modeset_lock_crtc);
193 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
196 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
197 * locking, and store the acquire ctx in the corresponding crtc. All other
198 * legacy operations take all locks and use a global acquire context. This
199 * function grabs the right one.
201 struct drm_modeset_acquire_ctx *
202 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
204 if (crtc->acquire_ctx)
205 return crtc->acquire_ctx;
207 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
209 return crtc->dev->mode_config.acquire_ctx;
211 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
214 * drm_modeset_unlock_crtc - drop crtc lock
217 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
218 * locks acquired through the hidden context.
220 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
222 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
227 crtc->acquire_ctx = NULL;
228 drm_modeset_drop_locks(ctx);
229 drm_modeset_acquire_fini(ctx);
233 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
236 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
239 * Useful as a debug assert.
241 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
243 struct drm_crtc *crtc;
245 /* Locking is currently fubar in the panic handler. */
250 if (oops_in_progress)
254 drm_for_each_crtc(crtc, dev)
255 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
257 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
258 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
260 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
263 * drm_modeset_acquire_init - initialize acquire context
264 * @ctx: the acquire context
267 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
270 memset(ctx, 0, sizeof(*ctx));
271 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
272 INIT_LIST_HEAD(&ctx->locked);
274 EXPORT_SYMBOL(drm_modeset_acquire_init);
277 * drm_modeset_acquire_fini - cleanup acquire context
278 * @ctx: the acquire context
280 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
282 ww_acquire_fini(&ctx->ww_ctx);
284 EXPORT_SYMBOL(drm_modeset_acquire_fini);
287 * drm_modeset_drop_locks - drop all locks
288 * @ctx: the acquire context
290 * Drop all locks currently held against this acquire context.
292 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
294 WARN_ON(ctx->contended);
295 while (!list_empty(&ctx->locked)) {
296 struct drm_modeset_lock_info *info;
298 info = list_first_entry(&ctx->locked,
299 struct drm_modeset_lock_info, ctx_entry);
301 drm_modeset_unlock(info->lock);
304 EXPORT_SYMBOL(drm_modeset_drop_locks);
306 static inline int modeset_lock(struct drm_modeset_lock *lock,
307 struct drm_modeset_acquire_ctx *ctx,
308 bool interruptible, bool slow)
312 WARN_ON(ctx->contended);
314 if (ctx->trylock_only) {
316 lockdep_assert_held(&ctx->ww_ctx);
319 if (!ww_mutex_trylock(&lock->mutex))
323 } else if (interruptible && slow) {
324 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
325 } else if (interruptible) {
326 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
328 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
331 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
333 if (ret == -EALREADY) {
334 /* we already hold the lock.. this is fine. For atomic
335 * we will need to be able to drm_modeset_lock() things
336 * without having to keep track of what is already locked
340 } else if (ret == -EDEADLK) {
341 ctx->contended = lock;
344 struct drm_modeset_lock_info *info;
346 info = kzalloc(sizeof(*info), GFP_KERNEL);
347 INIT_LIST_HEAD(&info->ctx_entry);
348 INIT_LIST_HEAD(&info->lock_entry);
351 list_add(&info->ctx_entry, &ctx->locked);
352 list_add(&info->lock_entry, &lock->locked);
358 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
361 struct drm_modeset_lock *contended = ctx->contended;
363 ctx->contended = NULL;
365 if (WARN_ON(!contended))
368 drm_modeset_drop_locks(ctx);
370 return modeset_lock(contended, ctx, interruptible, true);
374 * drm_modeset_backoff - deadlock avoidance backoff
375 * @ctx: the acquire context
377 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
378 * you must call this function to drop all currently held locks and
379 * block until the contended lock becomes available.
381 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
383 modeset_backoff(ctx, false);
385 EXPORT_SYMBOL(drm_modeset_backoff);
388 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
389 * @ctx: the acquire context
391 * Interruptible version of drm_modeset_backoff()
393 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
395 return modeset_backoff(ctx, true);
397 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
400 * drm_modeset_lock - take modeset lock
401 * @lock: lock to take
404 * If ctx is not NULL, then its ww acquire context is used and the
405 * lock will be tracked by the context and can be released by calling
406 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
407 * deadlock scenario has been detected and it is an error to attempt
408 * to take any more locks without first calling drm_modeset_backoff().
410 int drm_modeset_lock(struct drm_modeset_lock *lock,
411 struct drm_modeset_acquire_ctx *ctx)
414 return modeset_lock(lock, ctx, false, false);
416 ww_mutex_lock(&lock->mutex, NULL);
419 EXPORT_SYMBOL(drm_modeset_lock);
422 * drm_modeset_lock_interruptible - take modeset lock
423 * @lock: lock to take
426 * Interruptible version of drm_modeset_lock()
428 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
429 struct drm_modeset_acquire_ctx *ctx)
432 return modeset_lock(lock, ctx, true, false);
434 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
436 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
439 * drm_modeset_unlock - drop modeset lock
440 * @lock: lock to release
442 void drm_modeset_unlock(struct drm_modeset_lock *lock)
444 struct drm_modeset_lock_info *info;
446 /* undo in reverse order */
447 if (!list_empty(&lock->locked)) {
448 info = list_last_entry(&lock->locked,
449 struct drm_modeset_lock_info, lock_entry);
450 list_del_init(&info->lock_entry);
452 list_del_init(&info->ctx_entry);
455 ww_mutex_unlock(&lock->mutex);
457 EXPORT_SYMBOL(drm_modeset_unlock);
459 /* In some legacy codepaths it's convenient to just grab all the crtc and plane
461 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
462 struct drm_modeset_acquire_ctx *ctx)
464 struct drm_crtc *crtc;
465 struct drm_plane *plane;
468 drm_for_each_crtc(crtc, dev) {
469 ret = drm_modeset_lock(&crtc->mutex, ctx);
474 drm_for_each_plane(plane, dev) {
475 ret = drm_modeset_lock(&plane->mutex, ctx);
482 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);