2 * Copyright (C) 2014 Red Hat
3 * Author: Rob Clark <robdclark@gmail.com>
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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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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
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17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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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, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
44 * foreach (lock in random_ordered_set_of_locks) {
45 * ret = drm_modeset_lock(lock, ctx)
46 * if (ret == -EDEADLK) {
47 * ret = drm_modeset_backoff(ctx);
56 * drm_modeset_drop_locks(ctx);
57 * drm_modeset_acquire_fini(ctx);
59 * If all that is needed is a single modeset lock, then the &struct
60 * drm_modeset_acquire_ctx is not needed and the locking can be simplified
61 * by passing a NULL instead of ctx in the drm_modeset_lock() call or
62 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards
63 * call drm_modeset_unlock().
65 * On top of these per-object locks using &ww_mutex there's also an overall
66 * &drm_mode_config.mutex, for protecting everything else. Mostly this means
67 * probe state of connectors, and preventing hotplug add/removal of connectors.
69 * Finally there's a bunch of dedicated locks to protect drm core internal
70 * lists and lookup data structures.
73 static DEFINE_WW_CLASS(crtc_ww_class);
76 * drm_modeset_lock_all - take all modeset locks
79 * This function takes all modeset locks, suitable where a more fine-grained
80 * scheme isn't (yet) implemented. Locks must be dropped by calling the
81 * drm_modeset_unlock_all() function.
83 * This function is deprecated. It allocates a lock acquisition context and
84 * stores it in &drm_device.mode_config. This facilitate conversion of
85 * existing code because it removes the need to manually deal with the
86 * acquisition context, but it is also brittle because the context is global
87 * and care must be taken not to nest calls. New code should use the
88 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
90 void drm_modeset_lock_all(struct drm_device *dev)
92 struct drm_mode_config *config = &dev->mode_config;
93 struct drm_modeset_acquire_ctx *ctx;
96 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
100 mutex_lock(&config->mutex);
102 drm_modeset_acquire_init(ctx, 0);
105 ret = drm_modeset_lock_all_ctx(dev, ctx);
107 if (ret == -EDEADLK) {
108 drm_modeset_backoff(ctx);
112 drm_modeset_acquire_fini(ctx);
117 WARN_ON(config->acquire_ctx);
120 * We hold the locks now, so it is safe to stash the acquisition
121 * context for drm_modeset_unlock_all().
123 config->acquire_ctx = ctx;
125 drm_warn_on_modeset_not_all_locked(dev);
127 EXPORT_SYMBOL(drm_modeset_lock_all);
130 * drm_modeset_unlock_all - drop all modeset locks
133 * This function drops all modeset locks taken by a previous call to the
134 * drm_modeset_lock_all() function.
136 * This function is deprecated. It uses the lock acquisition context stored
137 * in &drm_device.mode_config. This facilitates conversion of existing
138 * code because it removes the need to manually deal with the acquisition
139 * context, but it is also brittle because the context is global and care must
140 * be taken not to nest calls. New code should pass the acquisition context
141 * directly to the drm_modeset_drop_locks() function.
143 void drm_modeset_unlock_all(struct drm_device *dev)
145 struct drm_mode_config *config = &dev->mode_config;
146 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
151 config->acquire_ctx = NULL;
152 drm_modeset_drop_locks(ctx);
153 drm_modeset_acquire_fini(ctx);
157 mutex_unlock(&dev->mode_config.mutex);
159 EXPORT_SYMBOL(drm_modeset_unlock_all);
162 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
165 * Useful as a debug assert.
167 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
169 struct drm_crtc *crtc;
171 /* Locking is currently fubar in the panic handler. */
176 if (oops_in_progress)
180 drm_for_each_crtc(crtc, dev)
181 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
183 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
184 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
186 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
189 * drm_modeset_acquire_init - initialize acquire context
190 * @ctx: the acquire context
191 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
193 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
194 * all calls to drm_modeset_lock() will perform an interruptible
197 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
200 memset(ctx, 0, sizeof(*ctx));
201 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
202 INIT_LIST_HEAD(&ctx->locked);
204 if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
205 ctx->interruptible = true;
207 EXPORT_SYMBOL(drm_modeset_acquire_init);
210 * drm_modeset_acquire_fini - cleanup acquire context
211 * @ctx: the acquire context
213 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
215 ww_acquire_fini(&ctx->ww_ctx);
217 EXPORT_SYMBOL(drm_modeset_acquire_fini);
220 * drm_modeset_drop_locks - drop all locks
221 * @ctx: the acquire context
223 * Drop all locks currently held against this acquire context.
225 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
227 WARN_ON(ctx->contended);
228 while (!list_empty(&ctx->locked)) {
229 struct drm_modeset_lock_info *info;
231 info = list_first_entry(&ctx->locked,
232 struct drm_modeset_lock_info, ctx_entry);
234 drm_modeset_unlock(info->lock);
237 EXPORT_SYMBOL(drm_modeset_drop_locks);
239 static inline int modeset_lock(struct drm_modeset_lock *lock,
240 struct drm_modeset_acquire_ctx *ctx,
241 bool interruptible, bool slow)
245 WARN_ON(ctx->contended);
247 if (ctx->trylock_only) {
249 lockdep_assert_held(&ctx->ww_ctx);
252 if (!ww_mutex_trylock(&lock->mutex))
256 } else if (interruptible && slow) {
257 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
258 } else if (interruptible) {
259 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
261 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
264 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
266 if (ret == -EALREADY) {
267 /* we already hold the lock.. this is fine. For atomic
268 * we will need to be able to drm_modeset_lock() things
269 * without having to keep track of what is already locked
273 } else if (ret == -EDEADLK) {
274 ctx->contended = lock;
277 struct drm_modeset_lock_info *info;
279 info = kzalloc(sizeof(*info), GFP_KERNEL);
280 INIT_LIST_HEAD(&info->ctx_entry);
281 INIT_LIST_HEAD(&info->lock_entry);
284 list_add(&info->ctx_entry, &ctx->locked);
285 list_add(&info->lock_entry, &lock->head);
292 * drm_modeset_backoff - deadlock avoidance backoff
293 * @ctx: the acquire context
295 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
296 * you must call this function to drop all currently held locks and
297 * block until the contended lock becomes available.
299 * This function returns 0 on success, or -ERESTARTSYS if this context
300 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
301 * wait has been interrupted.
303 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
305 struct drm_modeset_lock *contended = ctx->contended;
307 ctx->contended = NULL;
309 if (WARN_ON(!contended))
312 drm_modeset_drop_locks(ctx);
314 return modeset_lock(contended, ctx, ctx->interruptible, true);
316 EXPORT_SYMBOL(drm_modeset_backoff);
319 * drm_modeset_lock_init - initialize lock
320 * @lock: lock to init
322 void drm_modeset_lock_init(struct drm_modeset_lock *lock)
324 ww_mutex_init(&lock->mutex, &crtc_ww_class);
325 INIT_LIST_HEAD(&lock->head);
327 EXPORT_SYMBOL(drm_modeset_lock_init);
330 * drm_modeset_lock - take modeset lock
331 * @lock: lock to take
334 * If @ctx is not NULL, then its ww acquire context is used and the
335 * lock will be tracked by the context and can be released by calling
336 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
337 * deadlock scenario has been detected and it is an error to attempt
338 * to take any more locks without first calling drm_modeset_backoff().
340 * If the @ctx is not NULL and initialized with
341 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
342 * -ERESTARTSYS when interrupted.
344 * If @ctx is NULL then the function call behaves like a normal,
345 * uninterruptible non-nesting mutex_lock() call.
347 int drm_modeset_lock(struct drm_modeset_lock *lock,
348 struct drm_modeset_acquire_ctx *ctx)
351 return modeset_lock(lock, ctx, ctx->interruptible, false);
353 ww_mutex_lock(&lock->mutex, NULL);
356 EXPORT_SYMBOL(drm_modeset_lock);
359 * drm_modeset_lock_single_interruptible - take a single modeset lock
360 * @lock: lock to take
362 * This function behaves as drm_modeset_lock() with a NULL context,
363 * but performs interruptible waits.
365 * This function returns 0 on success, or -ERESTARTSYS when interrupted.
367 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
369 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
371 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
374 * drm_modeset_unlock - drop modeset lock
375 * @lock: lock to release
377 void drm_modeset_unlock(struct drm_modeset_lock *lock)
379 struct drm_modeset_lock_info *info;
381 /* undo in reverse order */
382 if (!list_empty(&lock->head)) {
383 info = list_last_entry(&lock->head,
384 struct drm_modeset_lock_info, lock_entry);
385 list_del_init(&info->lock_entry);
387 list_del_init(&info->ctx_entry);
390 ww_mutex_unlock(&lock->mutex);
392 EXPORT_SYMBOL(drm_modeset_unlock);
395 * drm_modeset_lock_all_ctx - take all modeset locks
397 * @ctx: lock acquisition context
399 * This function takes all modeset locks, suitable where a more fine-grained
400 * scheme isn't (yet) implemented.
402 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
403 * since that lock isn't required for modeset state changes. Callers which
404 * need to grab that lock too need to do so outside of the acquire context
407 * Locks acquired with this function should be released by calling the
408 * drm_modeset_drop_locks() function on @ctx.
410 * Returns: 0 on success or a negative error-code on failure.
412 int drm_modeset_lock_all_ctx(struct drm_device *dev,
413 struct drm_modeset_acquire_ctx *ctx)
415 struct drm_crtc *crtc;
416 struct drm_plane *plane;
419 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
423 drm_for_each_crtc(crtc, dev) {
424 ret = drm_modeset_lock(&crtc->mutex, ctx);
429 drm_for_each_plane(plane, dev) {
430 ret = drm_modeset_lock(&plane->mutex, ctx);
437 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);