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 &struct drm_modeset_lock and &struct 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);
55 * On top of of these per-object locks using &ww_mutex there's also an overall
56 * &drm_mode_config.mutex, for protecting everything else. Mostly this means
57 * probe state of connectors, and preventing hotplug add/removal of connectors.
59 * Finally there's a bunch of dedicated locks to protect drm core internal
60 * lists and lookup data structures.
63 static DEFINE_WW_CLASS(crtc_ww_class);
66 * drm_modeset_lock_all - take all modeset locks
69 * This function takes all modeset locks, suitable where a more fine-grained
70 * scheme isn't (yet) implemented. Locks must be dropped by calling the
71 * drm_modeset_unlock_all() function.
73 * This function is deprecated. It allocates a lock acquisition context and
74 * stores it in &drm_device.mode_config. This facilitate conversion of
75 * existing code because it removes the need to manually deal with the
76 * acquisition context, but it is also brittle because the context is global
77 * and care must be taken not to nest calls. New code should use the
78 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
80 void drm_modeset_lock_all(struct drm_device *dev)
82 struct drm_mode_config *config = &dev->mode_config;
83 struct drm_modeset_acquire_ctx *ctx;
86 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
90 mutex_lock(&config->mutex);
92 drm_modeset_acquire_init(ctx, 0);
95 ret = drm_modeset_lock_all_ctx(dev, ctx);
97 if (ret == -EDEADLK) {
98 drm_modeset_backoff(ctx);
102 drm_modeset_acquire_fini(ctx);
107 WARN_ON(config->acquire_ctx);
110 * We hold the locks now, so it is safe to stash the acquisition
111 * context for drm_modeset_unlock_all().
113 config->acquire_ctx = ctx;
115 drm_warn_on_modeset_not_all_locked(dev);
117 EXPORT_SYMBOL(drm_modeset_lock_all);
120 * drm_modeset_unlock_all - drop all modeset locks
123 * This function drops all modeset locks taken by a previous call to the
124 * drm_modeset_lock_all() function.
126 * This function is deprecated. It uses the lock acquisition context stored
127 * in &drm_device.mode_config. This facilitates conversion of existing
128 * code because it removes the need to manually deal with the acquisition
129 * context, but it is also brittle because the context is global and care must
130 * be taken not to nest calls. New code should pass the acquisition context
131 * directly to the drm_modeset_drop_locks() function.
133 void drm_modeset_unlock_all(struct drm_device *dev)
135 struct drm_mode_config *config = &dev->mode_config;
136 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
141 config->acquire_ctx = NULL;
142 drm_modeset_drop_locks(ctx);
143 drm_modeset_acquire_fini(ctx);
147 mutex_unlock(&dev->mode_config.mutex);
149 EXPORT_SYMBOL(drm_modeset_unlock_all);
152 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
155 * Useful as a debug assert.
157 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
159 struct drm_crtc *crtc;
161 /* Locking is currently fubar in the panic handler. */
166 if (oops_in_progress)
170 drm_for_each_crtc(crtc, dev)
171 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
173 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
174 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
176 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
179 * drm_modeset_acquire_init - initialize acquire context
180 * @ctx: the acquire context
183 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
186 memset(ctx, 0, sizeof(*ctx));
187 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
188 INIT_LIST_HEAD(&ctx->locked);
190 EXPORT_SYMBOL(drm_modeset_acquire_init);
193 * drm_modeset_acquire_fini - cleanup acquire context
194 * @ctx: the acquire context
196 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
198 ww_acquire_fini(&ctx->ww_ctx);
200 EXPORT_SYMBOL(drm_modeset_acquire_fini);
203 * drm_modeset_drop_locks - drop all locks
204 * @ctx: the acquire context
206 * Drop all locks currently held against this acquire context.
208 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
210 WARN_ON(ctx->contended);
211 while (!list_empty(&ctx->locked)) {
212 struct drm_modeset_lock_info *info;
214 info = list_first_entry(&ctx->locked,
215 struct drm_modeset_lock_info, ctx_entry);
217 drm_modeset_unlock(info->lock);
220 EXPORT_SYMBOL(drm_modeset_drop_locks);
222 static inline int modeset_lock(struct drm_modeset_lock *lock,
223 struct drm_modeset_acquire_ctx *ctx,
224 bool interruptible, bool slow)
228 WARN_ON(ctx->contended);
230 if (ctx->trylock_only) {
232 lockdep_assert_held(&ctx->ww_ctx);
235 if (!ww_mutex_trylock(&lock->mutex))
239 } else if (interruptible && slow) {
240 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
241 } else if (interruptible) {
242 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
244 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
247 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
249 if (ret == -EALREADY) {
250 /* we already hold the lock.. this is fine. For atomic
251 * we will need to be able to drm_modeset_lock() things
252 * without having to keep track of what is already locked
256 } else if (ret == -EDEADLK) {
257 ctx->contended = lock;
260 struct drm_modeset_lock_info *info;
262 info = kzalloc(sizeof(*info), GFP_KERNEL);
263 INIT_LIST_HEAD(&info->ctx_entry);
264 INIT_LIST_HEAD(&info->lock_entry);
267 list_add(&info->ctx_entry, &ctx->locked);
268 list_add(&info->lock_entry, &lock->head);
274 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
277 struct drm_modeset_lock *contended = ctx->contended;
279 ctx->contended = NULL;
281 if (WARN_ON(!contended))
284 drm_modeset_drop_locks(ctx);
286 return modeset_lock(contended, ctx, interruptible, true);
290 * drm_modeset_backoff - deadlock avoidance backoff
291 * @ctx: the acquire context
293 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
294 * you must call this function to drop all currently held locks and
295 * block until the contended lock becomes available.
297 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
299 modeset_backoff(ctx, false);
301 EXPORT_SYMBOL(drm_modeset_backoff);
304 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
305 * @ctx: the acquire context
307 * Interruptible version of drm_modeset_backoff()
309 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
311 return modeset_backoff(ctx, true);
313 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
316 * drm_modeset_lock_init - initialize lock
317 * @lock: lock to init
319 void drm_modeset_lock_init(struct drm_modeset_lock *lock)
321 ww_mutex_init(&lock->mutex, &crtc_ww_class);
322 INIT_LIST_HEAD(&lock->head);
324 EXPORT_SYMBOL(drm_modeset_lock_init);
327 * drm_modeset_lock - take modeset lock
328 * @lock: lock to take
331 * If ctx is not NULL, then its ww acquire context is used and the
332 * lock will be tracked by the context and can be released by calling
333 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
334 * deadlock scenario has been detected and it is an error to attempt
335 * to take any more locks without first calling drm_modeset_backoff().
337 int drm_modeset_lock(struct drm_modeset_lock *lock,
338 struct drm_modeset_acquire_ctx *ctx)
341 return modeset_lock(lock, ctx, false, false);
343 ww_mutex_lock(&lock->mutex, NULL);
346 EXPORT_SYMBOL(drm_modeset_lock);
349 * drm_modeset_lock_interruptible - take modeset lock
350 * @lock: lock to take
353 * Interruptible version of drm_modeset_lock()
355 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
356 struct drm_modeset_acquire_ctx *ctx)
359 return modeset_lock(lock, ctx, true, false);
361 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
363 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
366 * drm_modeset_unlock - drop modeset lock
367 * @lock: lock to release
369 void drm_modeset_unlock(struct drm_modeset_lock *lock)
371 struct drm_modeset_lock_info *info;
373 /* undo in reverse order */
374 if (!list_empty(&lock->head)) {
375 info = list_last_entry(&lock->head,
376 struct drm_modeset_lock_info, lock_entry);
377 list_del_init(&info->lock_entry);
379 list_del_init(&info->ctx_entry);
382 ww_mutex_unlock(&lock->mutex);
384 EXPORT_SYMBOL(drm_modeset_unlock);
387 * drm_modeset_lock_all_ctx - take all modeset locks
389 * @ctx: lock acquisition context
391 * This function takes all modeset locks, suitable where a more fine-grained
392 * scheme isn't (yet) implemented.
394 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
395 * since that lock isn't required for modeset state changes. Callers which
396 * need to grab that lock too need to do so outside of the acquire context
399 * Locks acquired with this function should be released by calling the
400 * drm_modeset_drop_locks() function on @ctx.
402 * Returns: 0 on success or a negative error-code on failure.
404 int drm_modeset_lock_all_ctx(struct drm_device *dev,
405 struct drm_modeset_acquire_ctx *ctx)
407 struct drm_crtc *crtc;
408 struct drm_plane *plane;
411 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
415 drm_for_each_crtc(crtc, dev) {
416 ret = drm_modeset_lock(&crtc->mutex, ctx);
421 drm_for_each_plane(plane, dev) {
422 ret = drm_modeset_lock(&plane->mutex, ctx);
429 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);