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"),
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12 * The above copyright notice and this permission notice shall be included in
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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 * For convenience this control flow is implemented in
60 * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
61 * where all modeset locks need to be taken through drm_modeset_lock_all_ctx().
63 * If all that is needed is a single modeset lock, then the &struct
64 * drm_modeset_acquire_ctx is not needed and the locking can be simplified
65 * by passing a NULL instead of ctx in the drm_modeset_lock() call or
66 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards
67 * call drm_modeset_unlock().
69 * On top of these per-object locks using &ww_mutex there's also an overall
70 * &drm_mode_config.mutex, for protecting everything else. Mostly this means
71 * probe state of connectors, and preventing hotplug add/removal of connectors.
73 * Finally there's a bunch of dedicated locks to protect drm core internal
74 * lists and lookup data structures.
77 static DEFINE_WW_CLASS(crtc_ww_class);
80 * drm_modeset_lock_all - take all modeset locks
83 * This function takes all modeset locks, suitable where a more fine-grained
84 * scheme isn't (yet) implemented. Locks must be dropped by calling the
85 * drm_modeset_unlock_all() function.
87 * This function is deprecated. It allocates a lock acquisition context and
88 * stores it in &drm_device.mode_config. This facilitate conversion of
89 * existing code because it removes the need to manually deal with the
90 * acquisition context, but it is also brittle because the context is global
91 * and care must be taken not to nest calls. New code should use the
92 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
94 void drm_modeset_lock_all(struct drm_device *dev)
96 struct drm_mode_config *config = &dev->mode_config;
97 struct drm_modeset_acquire_ctx *ctx;
100 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
104 mutex_lock(&config->mutex);
106 drm_modeset_acquire_init(ctx, 0);
109 ret = drm_modeset_lock_all_ctx(dev, ctx);
111 if (ret == -EDEADLK) {
112 drm_modeset_backoff(ctx);
116 drm_modeset_acquire_fini(ctx);
120 ww_acquire_done(&ctx->ww_ctx);
122 WARN_ON(config->acquire_ctx);
125 * We hold the locks now, so it is safe to stash the acquisition
126 * context for drm_modeset_unlock_all().
128 config->acquire_ctx = ctx;
130 drm_warn_on_modeset_not_all_locked(dev);
132 EXPORT_SYMBOL(drm_modeset_lock_all);
135 * drm_modeset_unlock_all - drop all modeset locks
138 * This function drops all modeset locks taken by a previous call to the
139 * drm_modeset_lock_all() function.
141 * This function is deprecated. It uses the lock acquisition context stored
142 * in &drm_device.mode_config. This facilitates conversion of existing
143 * code because it removes the need to manually deal with the acquisition
144 * context, but it is also brittle because the context is global and care must
145 * be taken not to nest calls. New code should pass the acquisition context
146 * directly to the drm_modeset_drop_locks() function.
148 void drm_modeset_unlock_all(struct drm_device *dev)
150 struct drm_mode_config *config = &dev->mode_config;
151 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
156 config->acquire_ctx = NULL;
157 drm_modeset_drop_locks(ctx);
158 drm_modeset_acquire_fini(ctx);
162 mutex_unlock(&dev->mode_config.mutex);
164 EXPORT_SYMBOL(drm_modeset_unlock_all);
167 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
170 * Useful as a debug assert.
172 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
174 struct drm_crtc *crtc;
176 /* Locking is currently fubar in the panic handler. */
177 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 *lock;
231 lock = list_first_entry(&ctx->locked,
232 struct drm_modeset_lock, head);
234 drm_modeset_unlock(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) {
248 lockdep_assert_held(&ctx->ww_ctx);
250 if (!ww_mutex_trylock(&lock->mutex))
254 } else if (interruptible && slow) {
255 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
256 } else if (interruptible) {
257 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
259 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
262 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
265 WARN_ON(!list_empty(&lock->head));
266 list_add(&lock->head, &ctx->locked);
267 } else if (ret == -EALREADY) {
268 /* we already hold the lock.. this is fine. For atomic
269 * we will need to be able to drm_modeset_lock() things
270 * without having to keep track of what is already locked
274 } else if (ret == -EDEADLK) {
275 ctx->contended = lock;
282 * drm_modeset_backoff - deadlock avoidance backoff
283 * @ctx: the acquire context
285 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
286 * you must call this function to drop all currently held locks and
287 * block until the contended lock becomes available.
289 * This function returns 0 on success, or -ERESTARTSYS if this context
290 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
291 * wait has been interrupted.
293 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
295 struct drm_modeset_lock *contended = ctx->contended;
297 ctx->contended = NULL;
299 if (WARN_ON(!contended))
302 drm_modeset_drop_locks(ctx);
304 return modeset_lock(contended, ctx, ctx->interruptible, true);
306 EXPORT_SYMBOL(drm_modeset_backoff);
309 * drm_modeset_lock_init - initialize lock
310 * @lock: lock to init
312 void drm_modeset_lock_init(struct drm_modeset_lock *lock)
314 ww_mutex_init(&lock->mutex, &crtc_ww_class);
315 INIT_LIST_HEAD(&lock->head);
317 EXPORT_SYMBOL(drm_modeset_lock_init);
320 * drm_modeset_lock - take modeset lock
321 * @lock: lock to take
324 * If @ctx is not NULL, then its ww acquire context is used and the
325 * lock will be tracked by the context and can be released by calling
326 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
327 * deadlock scenario has been detected and it is an error to attempt
328 * to take any more locks without first calling drm_modeset_backoff().
330 * If the @ctx is not NULL and initialized with
331 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
332 * -ERESTARTSYS when interrupted.
334 * If @ctx is NULL then the function call behaves like a normal,
335 * uninterruptible non-nesting mutex_lock() call.
337 int drm_modeset_lock(struct drm_modeset_lock *lock,
338 struct drm_modeset_acquire_ctx *ctx)
341 return modeset_lock(lock, ctx, ctx->interruptible, false);
343 ww_mutex_lock(&lock->mutex, NULL);
346 EXPORT_SYMBOL(drm_modeset_lock);
349 * drm_modeset_lock_single_interruptible - take a single modeset lock
350 * @lock: lock to take
352 * This function behaves as drm_modeset_lock() with a NULL context,
353 * but performs interruptible waits.
355 * This function returns 0 on success, or -ERESTARTSYS when interrupted.
357 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
359 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
361 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
364 * drm_modeset_unlock - drop modeset lock
365 * @lock: lock to release
367 void drm_modeset_unlock(struct drm_modeset_lock *lock)
369 list_del_init(&lock->head);
370 ww_mutex_unlock(&lock->mutex);
372 EXPORT_SYMBOL(drm_modeset_unlock);
375 * drm_modeset_lock_all_ctx - take all modeset locks
377 * @ctx: lock acquisition context
379 * This function takes all modeset locks, suitable where a more fine-grained
380 * scheme isn't (yet) implemented.
382 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
383 * since that lock isn't required for modeset state changes. Callers which
384 * need to grab that lock too need to do so outside of the acquire context
387 * Locks acquired with this function should be released by calling the
388 * drm_modeset_drop_locks() function on @ctx.
390 * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
392 * Returns: 0 on success or a negative error-code on failure.
394 int drm_modeset_lock_all_ctx(struct drm_device *dev,
395 struct drm_modeset_acquire_ctx *ctx)
397 struct drm_crtc *crtc;
398 struct drm_plane *plane;
401 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
405 drm_for_each_crtc(crtc, dev) {
406 ret = drm_modeset_lock(&crtc->mutex, ctx);
411 drm_for_each_plane(plane, dev) {
412 ret = drm_modeset_lock(&plane->mutex, ctx);
419 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);