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 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);
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 * dev->mode_config.lock, 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.
64 * drm_modeset_lock_all - take all modeset locks
67 * This function takes all modeset locks, suitable where a more fine-grained
68 * scheme isn't (yet) implemented. Locks must be dropped by calling the
69 * drm_modeset_unlock_all() function.
71 * This function is deprecated. It allocates a lock acquisition context and
72 * stores it in the DRM device's ->mode_config. This facilitate conversion of
73 * existing code because it removes the need to manually deal with the
74 * acquisition context, but it is also brittle because the context is global
75 * and care must be taken not to nest calls. New code should use the
76 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
78 void drm_modeset_lock_all(struct drm_device *dev)
80 struct drm_mode_config *config = &dev->mode_config;
81 struct drm_modeset_acquire_ctx *ctx;
84 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
88 mutex_lock(&config->mutex);
90 drm_modeset_acquire_init(ctx, 0);
93 ret = drm_modeset_lock_all_ctx(dev, ctx);
95 if (ret == -EDEADLK) {
96 drm_modeset_backoff(ctx);
100 drm_modeset_acquire_fini(ctx);
105 WARN_ON(config->acquire_ctx);
108 * We hold the locks now, so it is safe to stash the acquisition
109 * context for drm_modeset_unlock_all().
111 config->acquire_ctx = ctx;
113 drm_warn_on_modeset_not_all_locked(dev);
115 EXPORT_SYMBOL(drm_modeset_lock_all);
118 * drm_modeset_unlock_all - drop all modeset locks
121 * This function drops all modeset locks taken by a previous call to the
122 * drm_modeset_lock_all() function.
124 * This function is deprecated. It uses the lock acquisition context stored
125 * in the DRM device's ->mode_config. This facilitates conversion of existing
126 * code because it removes the need to manually deal with the acquisition
127 * context, but it is also brittle because the context is global and care must
128 * be taken not to nest calls. New code should pass the acquisition context
129 * directly to the drm_modeset_drop_locks() function.
131 void drm_modeset_unlock_all(struct drm_device *dev)
133 struct drm_mode_config *config = &dev->mode_config;
134 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
139 config->acquire_ctx = NULL;
140 drm_modeset_drop_locks(ctx);
141 drm_modeset_acquire_fini(ctx);
145 mutex_unlock(&dev->mode_config.mutex);
147 EXPORT_SYMBOL(drm_modeset_unlock_all);
150 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
152 * @plane: DRM plane to be updated on @crtc
154 * This function locks the given crtc and plane (which should be either the
155 * primary or cursor plane) using a hidden acquire context. This is necessary so
156 * that drivers internally using the atomic interfaces can grab further locks
157 * with the lock acquire context.
159 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
160 * converted to universal planes yet.
162 void drm_modeset_lock_crtc(struct drm_crtc *crtc,
163 struct drm_plane *plane)
165 struct drm_modeset_acquire_ctx *ctx;
168 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
172 drm_modeset_acquire_init(ctx, 0);
175 ret = drm_modeset_lock(&crtc->mutex, ctx);
180 ret = drm_modeset_lock(&plane->mutex, ctx);
185 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
191 WARN_ON(crtc->acquire_ctx);
193 /* now we hold the locks, so now that it is safe, stash the
194 * ctx for drm_modeset_unlock_crtc():
196 crtc->acquire_ctx = ctx;
201 if (ret == -EDEADLK) {
202 drm_modeset_backoff(ctx);
206 EXPORT_SYMBOL(drm_modeset_lock_crtc);
209 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
212 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
213 * locking, and store the acquire ctx in the corresponding crtc. All other
214 * legacy operations take all locks and use a global acquire context. This
215 * function grabs the right one.
217 struct drm_modeset_acquire_ctx *
218 drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
220 if (crtc->acquire_ctx)
221 return crtc->acquire_ctx;
223 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
225 return crtc->dev->mode_config.acquire_ctx;
227 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
230 * drm_modeset_unlock_crtc - drop crtc lock
233 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
234 * locks acquired through the hidden context.
236 void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
238 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
243 crtc->acquire_ctx = NULL;
244 drm_modeset_drop_locks(ctx);
245 drm_modeset_acquire_fini(ctx);
249 EXPORT_SYMBOL(drm_modeset_unlock_crtc);
252 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
255 * Useful as a debug assert.
257 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
259 struct drm_crtc *crtc;
261 /* Locking is currently fubar in the panic handler. */
262 if (oops_in_progress)
265 drm_for_each_crtc(crtc, dev)
266 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
268 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
269 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
271 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
274 * drm_modeset_acquire_init - initialize acquire context
275 * @ctx: the acquire context
278 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
281 memset(ctx, 0, sizeof(*ctx));
282 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
283 INIT_LIST_HEAD(&ctx->locked);
285 EXPORT_SYMBOL(drm_modeset_acquire_init);
288 * drm_modeset_acquire_fini - cleanup acquire context
289 * @ctx: the acquire context
291 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
293 ww_acquire_fini(&ctx->ww_ctx);
295 EXPORT_SYMBOL(drm_modeset_acquire_fini);
298 * drm_modeset_drop_locks - drop all locks
299 * @ctx: the acquire context
301 * Drop all locks currently held against this acquire context.
303 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
305 WARN_ON(ctx->contended);
306 while (!list_empty(&ctx->locked)) {
307 struct drm_modeset_lock *lock;
309 lock = list_first_entry(&ctx->locked,
310 struct drm_modeset_lock, head);
312 drm_modeset_unlock(lock);
315 EXPORT_SYMBOL(drm_modeset_drop_locks);
317 static inline int modeset_lock(struct drm_modeset_lock *lock,
318 struct drm_modeset_acquire_ctx *ctx,
319 bool interruptible, bool slow)
323 WARN_ON(ctx->contended);
325 if (ctx->trylock_only) {
326 lockdep_assert_held(&ctx->ww_ctx);
328 if (!ww_mutex_trylock(&lock->mutex))
332 } else if (interruptible && slow) {
333 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
334 } else if (interruptible) {
335 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
337 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
340 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
343 WARN_ON(!list_empty(&lock->head));
344 list_add(&lock->head, &ctx->locked);
345 } else if (ret == -EALREADY) {
346 /* we already hold the lock.. this is fine. For atomic
347 * we will need to be able to drm_modeset_lock() things
348 * without having to keep track of what is already locked
352 } else if (ret == -EDEADLK) {
353 ctx->contended = lock;
359 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
362 struct drm_modeset_lock *contended = ctx->contended;
364 ctx->contended = NULL;
366 if (WARN_ON(!contended))
369 drm_modeset_drop_locks(ctx);
371 return modeset_lock(contended, ctx, interruptible, true);
375 * drm_modeset_backoff - deadlock avoidance backoff
376 * @ctx: the acquire context
378 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
379 * you must call this function to drop all currently held locks and
380 * block until the contended lock becomes available.
382 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
384 modeset_backoff(ctx, false);
386 EXPORT_SYMBOL(drm_modeset_backoff);
389 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
390 * @ctx: the acquire context
392 * Interruptible version of drm_modeset_backoff()
394 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
396 return modeset_backoff(ctx, true);
398 EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
401 * drm_modeset_lock - take modeset lock
402 * @lock: lock to take
405 * If ctx is not NULL, then its ww acquire context is used and the
406 * lock will be tracked by the context and can be released by calling
407 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
408 * deadlock scenario has been detected and it is an error to attempt
409 * to take any more locks without first calling drm_modeset_backoff().
411 int drm_modeset_lock(struct drm_modeset_lock *lock,
412 struct drm_modeset_acquire_ctx *ctx)
415 return modeset_lock(lock, ctx, false, false);
417 ww_mutex_lock(&lock->mutex, NULL);
420 EXPORT_SYMBOL(drm_modeset_lock);
423 * drm_modeset_lock_interruptible - take modeset lock
424 * @lock: lock to take
427 * Interruptible version of drm_modeset_lock()
429 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
430 struct drm_modeset_acquire_ctx *ctx)
433 return modeset_lock(lock, ctx, true, false);
435 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
437 EXPORT_SYMBOL(drm_modeset_lock_interruptible);
440 * drm_modeset_unlock - drop modeset lock
441 * @lock: lock to release
443 void drm_modeset_unlock(struct drm_modeset_lock *lock)
445 list_del_init(&lock->head);
446 ww_mutex_unlock(&lock->mutex);
448 EXPORT_SYMBOL(drm_modeset_unlock);
451 * drm_modeset_lock_all_ctx - take all modeset locks
453 * @ctx: lock acquisition context
455 * This function takes all modeset locks, suitable where a more fine-grained
456 * scheme isn't (yet) implemented.
458 * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
459 * since that lock isn't required for modeset state changes. Callers which
460 * need to grab that lock too need to do so outside of the acquire context
463 * Locks acquired with this function should be released by calling the
464 * drm_modeset_drop_locks() function on @ctx.
466 * Returns: 0 on success or a negative error-code on failure.
468 int drm_modeset_lock_all_ctx(struct drm_device *dev,
469 struct drm_modeset_acquire_ctx *ctx)
471 struct drm_crtc *crtc;
472 struct drm_plane *plane;
475 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
479 drm_for_each_crtc(crtc, dev) {
480 ret = drm_modeset_lock(&crtc->mutex, ctx);
485 drm_for_each_plane(plane, dev) {
486 ret = drm_modeset_lock(&plane->mutex, ctx);
493 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);