1/*
  2 * Copyright (C) 2014 Red Hat
  3 * Author: Rob Clark <robdclark@gmail.com>
  4 *
  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:
 11 *
 12 * The above copyright notice and this permission notice shall be included in
 13 * all copies or substantial portions of the Software.
 14 *
 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.
 22 */
 23
 24#include <drm/drmP.h>
 25#include <drm/drm_crtc.h>
 26#include <drm/drm_modeset_lock.h>
 27
 28/**
 29 * DOC: kms locking
 30 *
 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.
 37 *
 38 * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.txt
 39 *
 40 * The basic usage pattern is to::
 41 *
 42 *     drm_modeset_acquire_init(&ctx)
 43 *     retry:
 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);
 48 *             goto retry;
 49 *         }
 50 *     }
 51 *     ... do stuff ...
 52 *     drm_modeset_drop_locks(&ctx);
 53 *     drm_modeset_acquire_fini(&ctx);
 54 *
 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.
 58 *
 59 * Finally there's a bunch of dedicated locks to protect drm core internal
 60 * lists and lookup data structures.
 61 */
 62
 63static DEFINE_WW_CLASS(crtc_ww_class);
 64
 65/**
 66 * drm_modeset_lock_all - take all modeset locks
 67 * @dev: DRM device
 68 *
 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.
 72 *
 73 * This function is deprecated. It allocates a lock acquisition context and
 74 * stores it in the DRM device's ->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.
 79 */
 80void drm_modeset_lock_all(struct drm_device *dev)
 81{
 82	struct drm_mode_config *config = &dev->mode_config;
 83	struct drm_modeset_acquire_ctx *ctx;
 84	int ret;
 85
 86	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 87	if (WARN_ON(!ctx))
 88		return;
 89
 90	mutex_lock(&config->mutex);
 91
 92	drm_modeset_acquire_init(ctx, 0);
 93
 94retry:
 95	ret = drm_modeset_lock_all_ctx(dev, ctx);
 96	if (ret < 0) {
 97		if (ret == -EDEADLK) {
 98			drm_modeset_backoff(ctx);
 99			goto retry;
100		}
101
102		drm_modeset_acquire_fini(ctx);
103		kfree(ctx);
104		return;
105	}
106
107	WARN_ON(config->acquire_ctx);
108
109	/*
110	 * We hold the locks now, so it is safe to stash the acquisition
111	 * context for drm_modeset_unlock_all().
112	 */
113	config->acquire_ctx = ctx;
114
115	drm_warn_on_modeset_not_all_locked(dev);
116}
117EXPORT_SYMBOL(drm_modeset_lock_all);
118
119/**
120 * drm_modeset_unlock_all - drop all modeset locks
121 * @dev: DRM device
122 *
123 * This function drops all modeset locks taken by a previous call to the
124 * drm_modeset_lock_all() function.
125 *
126 * This function is deprecated. It uses the lock acquisition context stored
127 * in the DRM device's ->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.
132 */
133void drm_modeset_unlock_all(struct drm_device *dev)
134{
135	struct drm_mode_config *config = &dev->mode_config;
136	struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
137
138	if (WARN_ON(!ctx))
139		return;
140
141	config->acquire_ctx = NULL;
142	drm_modeset_drop_locks(ctx);
143	drm_modeset_acquire_fini(ctx);
144
145	kfree(ctx);
146
147	mutex_unlock(&dev->mode_config.mutex);
148}
149EXPORT_SYMBOL(drm_modeset_unlock_all);
150
151/**
152 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
153 * @crtc: DRM CRTC
154 * @plane: DRM plane to be updated on @crtc
155 *
156 * This function locks the given crtc and plane (which should be either the
157 * primary or cursor plane) using a hidden acquire context. This is necessary so
158 * that drivers internally using the atomic interfaces can grab further locks
159 * with the lock acquire context.
160 *
161 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
162 * converted to universal planes yet.
163 */
164void drm_modeset_lock_crtc(struct drm_crtc *crtc,
165			   struct drm_plane *plane)
166{
167	struct drm_modeset_acquire_ctx *ctx;
168	int ret;
169
170	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
171	if (WARN_ON(!ctx))
172		return;
173
174	drm_modeset_acquire_init(ctx, 0);
175
176retry:
177	ret = drm_modeset_lock(&crtc->mutex, ctx);
178	if (ret)
179		goto fail;
180
181	if (plane) {
182		ret = drm_modeset_lock(&plane->mutex, ctx);
183		if (ret)
184			goto fail;
185
186		if (plane->crtc) {
187			ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
188			if (ret)
189				goto fail;
190		}
191	}
192
193	WARN_ON(crtc->acquire_ctx);
194
195	/* now we hold the locks, so now that it is safe, stash the
196	 * ctx for drm_modeset_unlock_crtc():
197	 */
198	crtc->acquire_ctx = ctx;
199
200	return;
201
202fail:
203	if (ret == -EDEADLK) {
204		drm_modeset_backoff(ctx);
205		goto retry;
206	}
207}
208EXPORT_SYMBOL(drm_modeset_lock_crtc);
209
210/**
211 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
212 * @crtc: drm crtc
213 *
214 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
215 * locking, and store the acquire ctx in the corresponding crtc. All other
216 * legacy operations take all locks and use a global acquire context. This
217 * function grabs the right one.
218 */
219struct drm_modeset_acquire_ctx *
220drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
221{
222	if (crtc->acquire_ctx)
223		return crtc->acquire_ctx;
224
225	WARN_ON(!crtc->dev->mode_config.acquire_ctx);
226
227	return crtc->dev->mode_config.acquire_ctx;
228}
229EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
230
231/**
232 * drm_modeset_unlock_crtc - drop crtc lock
233 * @crtc: drm crtc
234 *
235 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
236 * locks acquired through the hidden context.
237 */
238void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
239{
240	struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
241
242	if (WARN_ON(!ctx))
243		return;
244
245	crtc->acquire_ctx = NULL;
246	drm_modeset_drop_locks(ctx);
247	drm_modeset_acquire_fini(ctx);
248
249	kfree(ctx);
250}
251EXPORT_SYMBOL(drm_modeset_unlock_crtc);
252
253/**
254 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
255 * @dev: device
256 *
257 * Useful as a debug assert.
258 */
259void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
260{
261	struct drm_crtc *crtc;
262
263	/* Locking is currently fubar in the panic handler. */
264	if (oops_in_progress)
265		return;
266
267	drm_for_each_crtc(crtc, dev)
268		WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
269
270	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
271	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
272}
273EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
274
275/**
276 * drm_modeset_acquire_init - initialize acquire context
277 * @ctx: the acquire context
278 * @flags: for future
279 */
280void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
281		uint32_t flags)
282{
283	memset(ctx, 0, sizeof(*ctx));
284	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
285	INIT_LIST_HEAD(&ctx->locked);
286}
287EXPORT_SYMBOL(drm_modeset_acquire_init);
288
289/**
290 * drm_modeset_acquire_fini - cleanup acquire context
291 * @ctx: the acquire context
292 */
293void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
294{
295	ww_acquire_fini(&ctx->ww_ctx);
296}
297EXPORT_SYMBOL(drm_modeset_acquire_fini);
298
299/**
300 * drm_modeset_drop_locks - drop all locks
301 * @ctx: the acquire context
302 *
303 * Drop all locks currently held against this acquire context.
304 */
305void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
306{
307	WARN_ON(ctx->contended);
308	while (!list_empty(&ctx->locked)) {
309		struct drm_modeset_lock *lock;
310
311		lock = list_first_entry(&ctx->locked,
312				struct drm_modeset_lock, head);
313
314		drm_modeset_unlock(lock);
315	}
316}
317EXPORT_SYMBOL(drm_modeset_drop_locks);
318
319static inline int modeset_lock(struct drm_modeset_lock *lock,
320		struct drm_modeset_acquire_ctx *ctx,
321		bool interruptible, bool slow)
322{
323	int ret;
324
325	WARN_ON(ctx->contended);
326
327	if (ctx->trylock_only) {
328		lockdep_assert_held(&ctx->ww_ctx);
329
330		if (!ww_mutex_trylock(&lock->mutex))
331			return -EBUSY;
332		else
333			return 0;
334	} else if (interruptible && slow) {
335		ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
336	} else if (interruptible) {
337		ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
338	} else if (slow) {
339		ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
340		ret = 0;
341	} else {
342		ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
343	}
344	if (!ret) {
345		WARN_ON(!list_empty(&lock->head));
346		list_add(&lock->head, &ctx->locked);
347	} else if (ret == -EALREADY) {
348		/* we already hold the lock.. this is fine.  For atomic
349		 * we will need to be able to drm_modeset_lock() things
350		 * without having to keep track of what is already locked
351		 * or not.
352		 */
353		ret = 0;
354	} else if (ret == -EDEADLK) {
355		ctx->contended = lock;
356	}
357
358	return ret;
359}
360
361static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
362		bool interruptible)
363{
364	struct drm_modeset_lock *contended = ctx->contended;
365
366	ctx->contended = NULL;
367
368	if (WARN_ON(!contended))
369		return 0;
370
371	drm_modeset_drop_locks(ctx);
372
373	return modeset_lock(contended, ctx, interruptible, true);
374}
375
376/**
377 * drm_modeset_backoff - deadlock avoidance backoff
378 * @ctx: the acquire context
379 *
380 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
381 * you must call this function to drop all currently held locks and
382 * block until the contended lock becomes available.
383 */
384void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
385{
386	modeset_backoff(ctx, false);
387}
388EXPORT_SYMBOL(drm_modeset_backoff);
389
390/**
391 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
392 * @ctx: the acquire context
393 *
394 * Interruptible version of drm_modeset_backoff()
395 */
396int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
397{
398	return modeset_backoff(ctx, true);
399}
400EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
401
402/**
403 * drm_modeset_lock_init - initialize lock
404 * @lock: lock to init
405 */
406void drm_modeset_lock_init(struct drm_modeset_lock *lock)
407{
408	ww_mutex_init(&lock->mutex, &crtc_ww_class);
409	INIT_LIST_HEAD(&lock->head);
410}
411EXPORT_SYMBOL(drm_modeset_lock_init);
412
413/**
414 * drm_modeset_lock - take modeset lock
415 * @lock: lock to take
416 * @ctx: acquire ctx
417 *
418 * If ctx is not NULL, then its ww acquire context is used and the
419 * lock will be tracked by the context and can be released by calling
420 * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
421 * deadlock scenario has been detected and it is an error to attempt
422 * to take any more locks without first calling drm_modeset_backoff().
423 */
424int drm_modeset_lock(struct drm_modeset_lock *lock,
425		struct drm_modeset_acquire_ctx *ctx)
426{
427	if (ctx)
428		return modeset_lock(lock, ctx, false, false);
429
430	ww_mutex_lock(&lock->mutex, NULL);
431	return 0;
432}
433EXPORT_SYMBOL(drm_modeset_lock);
434
435/**
436 * drm_modeset_lock_interruptible - take modeset lock
437 * @lock: lock to take
438 * @ctx: acquire ctx
439 *
440 * Interruptible version of drm_modeset_lock()
441 */
442int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
443		struct drm_modeset_acquire_ctx *ctx)
444{
445	if (ctx)
446		return modeset_lock(lock, ctx, true, false);
447
448	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
449}
450EXPORT_SYMBOL(drm_modeset_lock_interruptible);
451
452/**
453 * drm_modeset_unlock - drop modeset lock
454 * @lock: lock to release
455 */
456void drm_modeset_unlock(struct drm_modeset_lock *lock)
457{
458	list_del_init(&lock->head);
459	ww_mutex_unlock(&lock->mutex);
460}
461EXPORT_SYMBOL(drm_modeset_unlock);
462
463/**
464 * drm_modeset_lock_all_ctx - take all modeset locks
465 * @dev: DRM device
466 * @ctx: lock acquisition context
467 *
468 * This function takes all modeset locks, suitable where a more fine-grained
469 * scheme isn't (yet) implemented.
470 *
471 * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
472 * since that lock isn't required for modeset state changes. Callers which
473 * need to grab that lock too need to do so outside of the acquire context
474 * @ctx.
475 *
476 * Locks acquired with this function should be released by calling the
477 * drm_modeset_drop_locks() function on @ctx.
478 *
479 * Returns: 0 on success or a negative error-code on failure.
480 */
481int drm_modeset_lock_all_ctx(struct drm_device *dev,
482			     struct drm_modeset_acquire_ctx *ctx)
483{
484	struct drm_crtc *crtc;
485	struct drm_plane *plane;
486	int ret;
487
488	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
489	if (ret)
490		return ret;
491
492	drm_for_each_crtc(crtc, dev) {
493		ret = drm_modeset_lock(&crtc->mutex, ctx);
494		if (ret)
495			return ret;
496	}
497
498	drm_for_each_plane(plane, dev) {
499		ret = drm_modeset_lock(&plane->mutex, ctx);
500		if (ret)
501			return ret;
502	}
503
504	return 0;
505}
506EXPORT_SYMBOL(drm_modeset_lock_all_ctx);