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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16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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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 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 by calling the
64 * drm_modeset_unlock_all() function.
66 * This function is deprecated. It allocates a lock acquisition context and
67 * stores it in the DRM device's ->mode_config. This facilitate conversion of
68 * existing code because it removes the need to manually deal with the
69 * acquisition context, but it is also brittle because the context is global
70 * and care must be taken not to nest calls. New code should use the
71 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
73 void drm_modeset_lock_all(struct drm_device *dev)
75 struct drm_mode_config *config = &dev->mode_config;
76 struct drm_modeset_acquire_ctx *ctx;
79 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
83 mutex_lock(&config->mutex);
85 drm_modeset_acquire_init(ctx, 0);
88 ret = drm_modeset_lock_all_ctx(dev, ctx);
90 if (ret == -EDEADLK) {
91 drm_modeset_backoff(ctx);
95 drm_modeset_acquire_fini(ctx);
100 WARN_ON(config->acquire_ctx);
103 * We hold the locks now, so it is safe to stash the acquisition
104 * context for drm_modeset_unlock_all().
106 config->acquire_ctx = ctx;
108 drm_warn_on_modeset_not_all_locked(dev);
110 EXPORT_SYMBOL(drm_modeset_lock_all);
113 * drm_modeset_unlock_all - drop all modeset locks
116 * This function drops all modeset locks taken by a previous call to the
117 * drm_modeset_lock_all() function.
119 * This function is deprecated. It uses the lock acquisition context stored
120 * in the DRM device's ->mode_config. This facilitates conversion of existing
121 * code because it removes the need to manually deal with the acquisition
122 * context, but it is also brittle because the context is global and care must
123 * be taken not to nest calls. New code should pass the acquisition context
124 * directly to the drm_modeset_drop_locks() function.
126 void drm_modeset_unlock_all(struct drm_device *dev)
128 struct drm_mode_config *config = &dev->mode_config;
129 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
134 config->acquire_ctx = NULL;
135 drm_modeset_drop_locks(ctx);
136 drm_modeset_acquire_fini(ctx);
140 mutex_unlock(&dev->mode_config.mutex);
142 EXPORT_SYMBOL(drm_modeset_unlock_all);
145 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
147 * @plane: DRM plane to be updated on @crtc
149 * This function locks the given crtc and plane (which should be either the
150 * primary or cursor plane) using a hidden acquire context. This is necessary so
151 * that drivers internally using the atomic interfaces can grab further locks
152 * with the lock acquire context.
154 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
155 * converted to universal planes yet.
157 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
158 struct drm_plane *plane)
160 struct drm_modeset_acquire_ctx *ctx;
163 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
167 drm_modeset_acquire_init(ctx, 0);
170 ret = drm_modeset_lock(&crtc->mutex, ctx);
175 ret = drm_modeset_lock(&plane->mutex, ctx);
180 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
186 WARN_ON(crtc->acquire_ctx);
188 /* now we hold the locks, so now that it is safe, stash the
189 * ctx for drm_modeset_unlock_crtc():
191 crtc->acquire_ctx = ctx;
196 if (ret == -EDEADLK) {
197 drm_modeset_backoff(ctx);
201 EXPORT_SYMBOL(drm_modeset_lock_crtc);
204 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
207 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
208 * locking, and store the acquire ctx in the corresponding crtc. All other
209 * legacy operations take all locks and use a global acquire context. This
210 * function grabs the right one.
212 struct drm_modeset_acquire_ctx *
213 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
215 if (crtc->acquire_ctx)
216 return crtc->acquire_ctx;
218 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
220 return crtc->dev->mode_config.acquire_ctx;
222 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
225 * drm_modeset_unlock_crtc - drop crtc lock
228 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
229 * locks acquired through the hidden context.
231 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
233 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
238 crtc->acquire_ctx = NULL;
239 drm_modeset_drop_locks(ctx);
240 drm_modeset_acquire_fini(ctx);
244 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
247 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
250 * Useful as a debug assert.
252 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
254 struct drm_crtc *crtc;
256 /* Locking is currently fubar in the panic handler. */
257 if (oops_in_progress)
260 drm_for_each_crtc(crtc, dev)
261 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
263 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
264 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
266 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
269 * drm_modeset_acquire_init - initialize acquire context
270 * @ctx: the acquire context
273 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
276 memset(ctx, 0, sizeof(*ctx));
277 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
278 INIT_LIST_HEAD(&ctx->locked);
280 EXPORT_SYMBOL(drm_modeset_acquire_init);
283 * drm_modeset_acquire_fini - cleanup acquire context
284 * @ctx: the acquire context
286 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
288 ww_acquire_fini(&ctx->ww_ctx);
290 EXPORT_SYMBOL(drm_modeset_acquire_fini);
293 * drm_modeset_drop_locks - drop all locks
294 * @ctx: the acquire context
296 * Drop all locks currently held against this acquire context.
298 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
300 WARN_ON(ctx->contended);
301 while (!list_empty(&ctx->locked)) {
302 struct drm_modeset_lock *lock;
304 lock = list_first_entry(&ctx->locked,
305 struct drm_modeset_lock, head);
307 drm_modeset_unlock(lock);
310 EXPORT_SYMBOL(drm_modeset_drop_locks);
312 static inline int modeset_lock(struct drm_modeset_lock *lock,
313 struct drm_modeset_acquire_ctx *ctx,
314 bool interruptible, bool slow)
318 WARN_ON(ctx->contended);
320 if (ctx->trylock_only) {
321 lockdep_assert_held(&ctx->ww_ctx);
323 if (!ww_mutex_trylock(&lock->mutex))
327 } else if (interruptible && slow) {
328 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
329 } else if (interruptible) {
330 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
332 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
335 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
338 WARN_ON(!list_empty(&lock->head));
339 list_add(&lock->head, &ctx->locked);
340 } else if (ret == -EALREADY) {
341 /* we already hold the lock.. this is fine. For atomic
342 * we will need to be able to drm_modeset_lock() things
343 * without having to keep track of what is already locked
347 } else if (ret == -EDEADLK) {
348 ctx->contended = lock;
354 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
357 struct drm_modeset_lock *contended = ctx->contended;
359 ctx->contended = NULL;
361 if (WARN_ON(!contended))
364 drm_modeset_drop_locks(ctx);
366 return modeset_lock(contended, ctx, interruptible, true);
370 * drm_modeset_backoff - deadlock avoidance backoff
371 * @ctx: the acquire context
373 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
374 * you must call this function to drop all currently held locks and
375 * block until the contended lock becomes available.
377 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
379 modeset_backoff(ctx, false);
381 EXPORT_SYMBOL(drm_modeset_backoff);
384 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
385 * @ctx: the acquire context
387 * Interruptible version of drm_modeset_backoff()
389 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
391 return modeset_backoff(ctx, true);
393 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
396 * drm_modeset_lock - take modeset lock
397 * @lock: lock to take
400 * If ctx is not NULL, then its ww acquire context is used and the
401 * lock will be tracked by the context and can be released by calling
402 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
403 * deadlock scenario has been detected and it is an error to attempt
404 * to take any more locks without first calling drm_modeset_backoff().
406 int drm_modeset_lock(struct drm_modeset_lock *lock,
407 struct drm_modeset_acquire_ctx *ctx)
410 return modeset_lock(lock, ctx, false, false);
412 ww_mutex_lock(&lock->mutex, NULL);
415 EXPORT_SYMBOL(drm_modeset_lock);
418 * drm_modeset_lock_interruptible - take modeset lock
419 * @lock: lock to take
422 * Interruptible version of drm_modeset_lock()
424 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
425 struct drm_modeset_acquire_ctx *ctx)
428 return modeset_lock(lock, ctx, true, false);
430 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
432 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
435 * drm_modeset_unlock - drop modeset lock
436 * @lock: lock to release
438 void drm_modeset_unlock(struct drm_modeset_lock *lock)
440 list_del_init(&lock->head);
441 ww_mutex_unlock(&lock->mutex);
443 EXPORT_SYMBOL(drm_modeset_unlock);
446 * drm_modeset_lock_all_ctx - take all modeset locks
448 * @ctx: lock acquisition context
450 * This function takes all modeset locks, suitable where a more fine-grained
451 * scheme isn't (yet) implemented.
453 * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
454 * since that lock isn't required for modeset state changes. Callers which
455 * need to grab that lock too need to do so outside of the acquire context
458 * Locks acquired with this function should be released by calling the
459 * drm_modeset_drop_locks() function on @ctx.
461 * Returns: 0 on success or a negative error-code on failure.
463 int drm_modeset_lock_all_ctx(struct drm_device *dev,
464 struct drm_modeset_acquire_ctx *ctx)
466 struct drm_crtc *crtc;
467 struct drm_plane *plane;
470 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
474 drm_for_each_crtc(crtc, dev) {
475 ret = drm_modeset_lock(&crtc->mutex, ctx);
480 drm_for_each_plane(plane, dev) {
481 ret = drm_modeset_lock(&plane->mutex, ctx);
488 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);