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 - take all modeset locks
63 * This function takes all modeset locks, suitable where a more fine-grained
64 * scheme isn't (yet) implemented. Locks must be dropped with
65 * drm_modeset_unlock_all.
67 void drm_modeset_lock_all(struct drm_device *dev)
69 struct drm_mode_config *config = &dev->mode_config;
70 struct drm_modeset_acquire_ctx *ctx;
73 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
77 mutex_lock(&config->mutex);
79 drm_modeset_acquire_init(ctx, 0);
82 ret = drm_modeset_lock(&config->connection_mutex, ctx);
85 ret = drm_modeset_lock_all_crtcs(dev, ctx);
89 WARN_ON(config->acquire_ctx);
91 /* now we hold the locks, so now that it is safe, stash the
92 * ctx for drm_modeset_unlock_all():
94 config->acquire_ctx = ctx;
96 drm_warn_on_modeset_not_all_locked(dev);
101 if (ret == -EDEADLK) {
102 drm_modeset_backoff(ctx);
106 EXPORT_SYMBOL(drm_modeset_lock_all);
109 * drm_modeset_unlock_all - drop all modeset locks
112 * This function drop all modeset locks taken by drm_modeset_lock_all.
114 void drm_modeset_unlock_all(struct drm_device *dev)
116 struct drm_mode_config *config = &dev->mode_config;
117 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
122 config->acquire_ctx = NULL;
123 drm_modeset_drop_locks(ctx);
124 drm_modeset_acquire_fini(ctx);
128 mutex_unlock(&dev->mode_config.mutex);
130 EXPORT_SYMBOL(drm_modeset_unlock_all);
133 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx
136 * This function locks the given crtc using a hidden acquire context. This is
137 * necessary so that drivers internally using the atomic interfaces can grab
138 * further locks with the lock acquire context.
140 void drm_modeset_lock_crtc(struct drm_crtc *crtc)
142 struct drm_modeset_acquire_ctx *ctx;
145 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
149 drm_modeset_acquire_init(ctx, 0);
152 ret = drm_modeset_lock(&crtc->mutex, ctx);
156 WARN_ON(crtc->acquire_ctx);
158 /* now we hold the locks, so now that it is safe, stash the
159 * ctx for drm_modeset_unlock_crtc():
161 crtc->acquire_ctx = ctx;
166 if (ret == -EDEADLK) {
167 drm_modeset_backoff(ctx);
171 EXPORT_SYMBOL(drm_modeset_lock_crtc);
174 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
177 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
178 * locking, and store the acquire ctx in the corresponding crtc. All other
179 * legacy operations take all locks and use a global acquire context. This
180 * function grabs the right one.
182 struct drm_modeset_acquire_ctx *
183 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
185 if (crtc->acquire_ctx)
186 return crtc->acquire_ctx;
188 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
190 return crtc->dev->mode_config.acquire_ctx;
192 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
195 * drm_modeset_unlock_crtc - drop crtc lock
198 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
199 * locks acquired through the hidden context.
201 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
203 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
208 crtc->acquire_ctx = NULL;
209 drm_modeset_drop_locks(ctx);
210 drm_modeset_acquire_fini(ctx);
214 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
217 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
220 * Useful as a debug assert.
222 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
224 struct drm_crtc *crtc;
226 /* Locking is currently fubar in the panic handler. */
228 if (oops_in_progress)
232 list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
233 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
235 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
236 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
238 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
241 * drm_modeset_acquire_init - initialize acquire context
242 * @ctx: the acquire context
245 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
248 memset(ctx, 0, sizeof(*ctx));
249 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
250 INIT_LIST_HEAD(&ctx->locked);
252 EXPORT_SYMBOL(drm_modeset_acquire_init);
255 * drm_modeset_acquire_fini - cleanup acquire context
256 * @ctx: the acquire context
258 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
260 ww_acquire_fini(&ctx->ww_ctx);
262 EXPORT_SYMBOL(drm_modeset_acquire_fini);
265 * drm_modeset_drop_locks - drop all locks
266 * @ctx: the acquire context
268 * Drop all locks currently held against this acquire context.
270 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
272 WARN_ON(ctx->contended);
273 while (!list_empty(&ctx->locked)) {
274 struct drm_modeset_lock_info *info;
276 info = list_first_entry(&ctx->locked,
277 struct drm_modeset_lock_info, ctx_entry);
279 drm_modeset_unlock(info->lock);
282 EXPORT_SYMBOL(drm_modeset_drop_locks);
284 static inline int modeset_lock(struct drm_modeset_lock *lock,
285 struct drm_modeset_acquire_ctx *ctx,
286 bool interruptible, bool slow)
290 WARN_ON(ctx->contended);
292 if (interruptible && slow) {
293 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
294 } else if (interruptible) {
295 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
297 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
300 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
302 if (ret == -EALREADY) {
303 /* we already hold the lock.. this is fine. For atomic
304 * we will need to be able to drm_modeset_lock() things
305 * without having to keep track of what is already locked
309 } else if (ret == -EDEADLK) {
310 ctx->contended = lock;
313 struct drm_modeset_lock_info *info;
315 info = kzalloc(sizeof(*info), GFP_KERNEL);
316 INIT_LIST_HEAD(&info->ctx_entry);
317 INIT_LIST_HEAD(&info->lock_entry);
320 list_add(&info->ctx_entry, &ctx->locked);
321 list_add(&info->lock_entry, &lock->locked);
327 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
330 struct drm_modeset_lock *contended = ctx->contended;
332 ctx->contended = NULL;
334 if (WARN_ON(!contended))
337 drm_modeset_drop_locks(ctx);
339 return modeset_lock(contended, ctx, interruptible, true);
343 * drm_modeset_backoff - deadlock avoidance backoff
344 * @ctx: the acquire context
346 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
347 * you must call this function to drop all currently held locks and
348 * block until the contended lock becomes available.
350 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
352 modeset_backoff(ctx, false);
354 EXPORT_SYMBOL(drm_modeset_backoff);
357 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
358 * @ctx: the acquire context
360 * Interruptible version of drm_modeset_backoff()
362 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
364 return modeset_backoff(ctx, true);
366 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
369 * drm_modeset_lock - take modeset lock
370 * @lock: lock to take
373 * If ctx is not NULL, then its ww acquire context is used and the
374 * lock will be tracked by the context and can be released by calling
375 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
376 * deadlock scenario has been detected and it is an error to attempt
377 * to take any more locks without first calling drm_modeset_backoff().
379 int drm_modeset_lock(struct drm_modeset_lock *lock,
380 struct drm_modeset_acquire_ctx *ctx)
383 return modeset_lock(lock, ctx, false, false);
385 ww_mutex_lock(&lock->mutex, NULL);
388 EXPORT_SYMBOL(drm_modeset_lock);
391 * drm_modeset_lock_interruptible - take modeset lock
392 * @lock: lock to take
395 * Interruptible version of drm_modeset_lock()
397 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
398 struct drm_modeset_acquire_ctx *ctx)
401 return modeset_lock(lock, ctx, true, false);
403 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
405 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
408 * drm_modeset_unlock - drop modeset lock
409 * @lock: lock to release
411 void drm_modeset_unlock(struct drm_modeset_lock *lock)
413 struct drm_modeset_lock_info *info;
415 /* undo in reverse order */
416 if (!list_empty(&lock->locked)) {
417 info = list_last_entry(&lock->locked,
418 struct drm_modeset_lock_info, lock_entry);
419 list_del_init(&info->lock_entry);
421 list_del_init(&info->ctx_entry);
424 ww_mutex_unlock(&lock->mutex);
426 EXPORT_SYMBOL(drm_modeset_unlock);
428 /* Temporary.. until we have sufficiently fine grained locking, there
429 * are a couple scenarios where it is convenient to grab all crtc locks.
430 * It is planned to remove this:
432 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
433 struct drm_modeset_acquire_ctx *ctx)
435 struct drm_mode_config *config = &dev->mode_config;
436 struct drm_crtc *crtc;
439 list_for_each_entry(crtc, &config->crtc_list, head) {
440 ret = drm_modeset_lock(&crtc->mutex, ctx);
447 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);