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
 56/**
 57 * drm_modeset_lock_all - take all modeset locks
 58 * @dev: DRM device
 59 *
 60 * This function takes all modeset locks, suitable where a more fine-grained
 61 * scheme isn't (yet) implemented. Locks must be dropped by calling the
 62 * drm_modeset_unlock_all() function.
 63 *
 64 * This function is deprecated. It allocates a lock acquisition context and
 65 * stores it in the DRM device's ->mode_config. This facilitate conversion of
 66 * existing code because it removes the need to manually deal with the
 67 * acquisition context, but it is also brittle because the context is global
 68 * and care must be taken not to nest calls. New code should use the
 69 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
 70 */
 71void drm_modeset_lock_all(struct drm_device *dev)
 72{
 73	struct drm_mode_config *config = &dev->mode_config;
 74	struct drm_modeset_acquire_ctx *ctx;
 75	int ret;
 76
 77	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 78	if (WARN_ON(!ctx))
 79		return;
 80
 81	mutex_lock(&config->mutex);
 82
 83	drm_modeset_acquire_init(ctx, 0);
 84
 85retry:
 86	ret = drm_modeset_lock_all_ctx(dev, ctx);
 87	if (ret < 0) {
 88		if (ret == -EDEADLK) {
 89			drm_modeset_backoff(ctx);
 90			goto retry;
 91		}
 92
 93		drm_modeset_acquire_fini(ctx);
 94		kfree(ctx);
 95		return;
 96	}
 97
 98	WARN_ON(config->acquire_ctx);
 99
100	/*
101	 * We hold the locks now, so it is safe to stash the acquisition
102	 * context for drm_modeset_unlock_all().
103	 */
104	config->acquire_ctx = ctx;
105
106	drm_warn_on_modeset_not_all_locked(dev);
107}
108EXPORT_SYMBOL(drm_modeset_lock_all);
109
110/**
111 * drm_modeset_unlock_all - drop all modeset locks
112 * @dev: DRM device
113 *
114 * This function drops all modeset locks taken by a previous call to the
115 * drm_modeset_lock_all() function.
116 *
117 * This function is deprecated. It uses the lock acquisition context stored
118 * in the DRM device's ->mode_config. This facilitates conversion of existing
119 * code because it removes the need to manually deal with the acquisition
120 * context, but it is also brittle because the context is global and care must
121 * be taken not to nest calls. New code should pass the acquisition context
122 * directly to the drm_modeset_drop_locks() function.
123 */
124void drm_modeset_unlock_all(struct drm_device *dev)
125{
126	struct drm_mode_config *config = &dev->mode_config;
127	struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
128
129	if (WARN_ON(!ctx))
130		return;
131
132	config->acquire_ctx = NULL;
133	drm_modeset_drop_locks(ctx);
134	drm_modeset_acquire_fini(ctx);
135
136	kfree(ctx);
137
138	mutex_unlock(&dev->mode_config.mutex);
139}
140EXPORT_SYMBOL(drm_modeset_unlock_all);
141
142/**
143 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
144 * @crtc: DRM CRTC
145 * @plane: DRM plane to be updated on @crtc
146 *
147 * This function locks the given crtc and plane (which should be either the
148 * primary or cursor plane) using a hidden acquire context. This is necessary so
149 * that drivers internally using the atomic interfaces can grab further locks
150 * with the lock acquire context.
151 *
152 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
153 * converted to universal planes yet.
154 */
155void drm_modeset_lock_crtc(struct drm_crtc *crtc,
156			   struct drm_plane *plane)
157{
158	struct drm_modeset_acquire_ctx *ctx;
159	int ret;
160
161	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
162	if (WARN_ON(!ctx))
163		return;
164
165	drm_modeset_acquire_init(ctx, 0);
166
167retry:
168	ret = drm_modeset_lock(&crtc->mutex, ctx);
169	if (ret)
170		goto fail;
171
172	if (plane) {
173		ret = drm_modeset_lock(&plane->mutex, ctx);
174		if (ret)
175			goto fail;
176
177		if (plane->crtc) {
178			ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
179			if (ret)
180				goto fail;
181		}
182	}
183
184	WARN_ON(crtc->acquire_ctx);
185
186	/* now we hold the locks, so now that it is safe, stash the
187	 * ctx for drm_modeset_unlock_crtc():
188	 */
189	crtc->acquire_ctx = ctx;
190
191	return;
192
193fail:
194	if (ret == -EDEADLK) {
195		drm_modeset_backoff(ctx);
196		goto retry;
197	}
198}
199EXPORT_SYMBOL(drm_modeset_lock_crtc);
200
201/**
202 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
203 * @crtc: drm crtc
204 *
205 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
206 * locking, and store the acquire ctx in the corresponding crtc. All other
207 * legacy operations take all locks and use a global acquire context. This
208 * function grabs the right one.
209 */
210struct drm_modeset_acquire_ctx *
211drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
212{
213	if (crtc->acquire_ctx)
214		return crtc->acquire_ctx;
215
216	WARN_ON(!crtc->dev->mode_config.acquire_ctx);
217
218	return crtc->dev->mode_config.acquire_ctx;
219}
220EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
221
222/**
223 * drm_modeset_unlock_crtc - drop crtc lock
224 * @crtc: drm crtc
225 *
226 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
227 * locks acquired through the hidden context.
228 */
229void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
230{
231	struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
232
233	if (WARN_ON(!ctx))
234		return;
235
236	crtc->acquire_ctx = NULL;
237	drm_modeset_drop_locks(ctx);
238	drm_modeset_acquire_fini(ctx);
239
240	kfree(ctx);
241}
242EXPORT_SYMBOL(drm_modeset_unlock_crtc);
243
244/**
245 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
246 * @dev: device
247 *
248 * Useful as a debug assert.
249 */
250void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
251{
252	struct drm_crtc *crtc;
253
254	/* Locking is currently fubar in the panic handler. */
255	if (oops_in_progress)
256		return;
257
258	drm_for_each_crtc(crtc, dev)
259		WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
260
261	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
262	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
263}
264EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
265
266/**
267 * drm_modeset_acquire_init - initialize acquire context
268 * @ctx: the acquire context
269 * @flags: for future
270 */
271void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
272		uint32_t flags)
273{
274	memset(ctx, 0, sizeof(*ctx));
275	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
276	INIT_LIST_HEAD(&ctx->locked);
277}
278EXPORT_SYMBOL(drm_modeset_acquire_init);
279
280/**
281 * drm_modeset_acquire_fini - cleanup acquire context
282 * @ctx: the acquire context
283 */
284void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
285{
286	ww_acquire_fini(&ctx->ww_ctx);
287}
288EXPORT_SYMBOL(drm_modeset_acquire_fini);
289
290/**
291 * drm_modeset_drop_locks - drop all locks
292 * @ctx: the acquire context
293 *
294 * Drop all locks currently held against this acquire context.
295 */
296void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
297{
298	WARN_ON(ctx->contended);
299	while (!list_empty(&ctx->locked)) {
300		struct drm_modeset_lock *lock;
301
302		lock = list_first_entry(&ctx->locked,
303				struct drm_modeset_lock, head);
304
305		drm_modeset_unlock(lock);
306	}
307}
308EXPORT_SYMBOL(drm_modeset_drop_locks);
309
310static inline int modeset_lock(struct drm_modeset_lock *lock,
311		struct drm_modeset_acquire_ctx *ctx,
312		bool interruptible, bool slow)
313{
314	int ret;
315
316	WARN_ON(ctx->contended);
317
318	if (ctx->trylock_only) {
319		lockdep_assert_held(&ctx->ww_ctx);
320
321		if (!ww_mutex_trylock(&lock->mutex))
322			return -EBUSY;
323		else
324			return 0;
325	} else if (interruptible && slow) {
326		ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
327	} else if (interruptible) {
328		ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
329	} else if (slow) {
330		ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
331		ret = 0;
332	} else {
333		ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
334	}
335	if (!ret) {
336		WARN_ON(!list_empty(&lock->head));
337		list_add(&lock->head, &ctx->locked);
338	} else if (ret == -EALREADY) {
339		/* we already hold the lock.. this is fine.  For atomic
340		 * we will need to be able to drm_modeset_lock() things
341		 * without having to keep track of what is already locked
342		 * or not.
343		 */
344		ret = 0;
345	} else if (ret == -EDEADLK) {
346		ctx->contended = lock;
347	}
348
349	return ret;
350}
351
352static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
353		bool interruptible)
354{
355	struct drm_modeset_lock *contended = ctx->contended;
356
357	ctx->contended = NULL;
358
359	if (WARN_ON(!contended))
360		return 0;
361
362	drm_modeset_drop_locks(ctx);
363
364	return modeset_lock(contended, ctx, interruptible, true);
365}
366
367/**
368 * drm_modeset_backoff - deadlock avoidance backoff
369 * @ctx: the acquire context
370 *
371 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
372 * you must call this function to drop all currently held locks and
373 * block until the contended lock becomes available.
374 */
375void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
376{
377	modeset_backoff(ctx, false);
378}
379EXPORT_SYMBOL(drm_modeset_backoff);
380
381/**
382 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
383 * @ctx: the acquire context
384 *
385 * Interruptible version of drm_modeset_backoff()
386 */
387int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
388{
389	return modeset_backoff(ctx, true);
390}
391EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
392
393/**
394 * drm_modeset_lock - take modeset lock
395 * @lock: lock to take
396 * @ctx: acquire ctx
397 *
398 * If ctx is not NULL, then its ww acquire context is used and the
399 * lock will be tracked by the context and can be released by calling
400 * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
401 * deadlock scenario has been detected and it is an error to attempt
402 * to take any more locks without first calling drm_modeset_backoff().
403 */
404int drm_modeset_lock(struct drm_modeset_lock *lock,
405		struct drm_modeset_acquire_ctx *ctx)
406{
407	if (ctx)
408		return modeset_lock(lock, ctx, false, false);
409
410	ww_mutex_lock(&lock->mutex, NULL);
411	return 0;
412}
413EXPORT_SYMBOL(drm_modeset_lock);
414
415/**
416 * drm_modeset_lock_interruptible - take modeset lock
417 * @lock: lock to take
418 * @ctx: acquire ctx
419 *
420 * Interruptible version of drm_modeset_lock()
421 */
422int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
423		struct drm_modeset_acquire_ctx *ctx)
424{
425	if (ctx)
426		return modeset_lock(lock, ctx, true, false);
427
428	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
429}
430EXPORT_SYMBOL(drm_modeset_lock_interruptible);
431
432/**
433 * drm_modeset_unlock - drop modeset lock
434 * @lock: lock to release
435 */
436void drm_modeset_unlock(struct drm_modeset_lock *lock)
437{
438	list_del_init(&lock->head);
439	ww_mutex_unlock(&lock->mutex);
440}
441EXPORT_SYMBOL(drm_modeset_unlock);
442
443/**
444 * drm_modeset_lock_all_ctx - take all modeset locks
445 * @dev: DRM device
446 * @ctx: lock acquisition context
447 *
448 * This function takes all modeset locks, suitable where a more fine-grained
449 * scheme isn't (yet) implemented.
450 *
451 * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
452 * since that lock isn't required for modeset state changes. Callers which
453 * need to grab that lock too need to do so outside of the acquire context
454 * @ctx.
455 *
456 * Locks acquired with this function should be released by calling the
457 * drm_modeset_drop_locks() function on @ctx.
458 *
459 * Returns: 0 on success or a negative error-code on failure.
460 */
461int drm_modeset_lock_all_ctx(struct drm_device *dev,
462			     struct drm_modeset_acquire_ctx *ctx)
463{
464	struct drm_crtc *crtc;
465	struct drm_plane *plane;
466	int ret;
467
468	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
469	if (ret)
470		return ret;
471
472	drm_for_each_crtc(crtc, dev) {
473		ret = drm_modeset_lock(&crtc->mutex, ctx);
474		if (ret)
475			return ret;
476	}
477
478	drm_for_each_plane(plane, dev) {
479		ret = drm_modeset_lock(&plane->mutex, ctx);
480		if (ret)
481			return ret;
482	}
483
484	return 0;
485}
486EXPORT_SYMBOL(drm_modeset_lock_all_ctx);