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 &struct drm_modeset_lock and &struct 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, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
 43 *     retry:
 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);
 48 *             if (!ret)
 49 *                 goto retry;
 50 *         }
 51 *         if (ret)
 52 *             goto out;
 53 *     }
 54 *     ... do stuff ...
 55 *     out:
 56 *     drm_modeset_drop_locks(ctx);
 57 *     drm_modeset_acquire_fini(ctx);
 58 *
 59 * If all that is needed is a single modeset lock, then the &struct
 60 * drm_modeset_acquire_ctx is not needed and the locking can be simplified
 61 * by passing a NULL instead of ctx in the drm_modeset_lock() call or
 62 * calling  drm_modeset_lock_single_interruptible(). To unlock afterwards
 63 * call drm_modeset_unlock().
 64 *
 65 * On top of these per-object locks using &ww_mutex there's also an overall
 66 * &drm_mode_config.mutex, for protecting everything else. Mostly this means
 67 * probe state of connectors, and preventing hotplug add/removal of connectors.
 68 *
 69 * Finally there's a bunch of dedicated locks to protect drm core internal
 70 * lists and lookup data structures.
 71 */
 72
 73static DEFINE_WW_CLASS(crtc_ww_class);
 74
 75/**
 76 * drm_modeset_lock_all - take all modeset locks
 77 * @dev: DRM device
 78 *
 79 * This function takes all modeset locks, suitable where a more fine-grained
 80 * scheme isn't (yet) implemented. Locks must be dropped by calling the
 81 * drm_modeset_unlock_all() function.
 82 *
 83 * This function is deprecated. It allocates a lock acquisition context and
 84 * stores it in &drm_device.mode_config. This facilitate conversion of
 85 * existing code because it removes the need to manually deal with the
 86 * acquisition context, but it is also brittle because the context is global
 87 * and care must be taken not to nest calls. New code should use the
 88 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
 89 */
 90void drm_modeset_lock_all(struct drm_device *dev)
 91{
 92	struct drm_mode_config *config = &dev->mode_config;
 93	struct drm_modeset_acquire_ctx *ctx;
 94	int ret;
 95
 96	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
 97	if (WARN_ON(!ctx))
 98		return;
 99
100	mutex_lock(&config->mutex);
101
102	drm_modeset_acquire_init(ctx, 0);
103
104retry:
105	ret = drm_modeset_lock_all_ctx(dev, ctx);
106	if (ret < 0) {
107		if (ret == -EDEADLK) {
108			drm_modeset_backoff(ctx);
109			goto retry;
110		}
111
112		drm_modeset_acquire_fini(ctx);
113		kfree(ctx);
114		return;
115	}
116	ww_acquire_done(&ctx->ww_ctx);
117
118	WARN_ON(config->acquire_ctx);
119
120	/*
121	 * We hold the locks now, so it is safe to stash the acquisition
122	 * context for drm_modeset_unlock_all().
123	 */
124	config->acquire_ctx = ctx;
125
126	drm_warn_on_modeset_not_all_locked(dev);
127}
128EXPORT_SYMBOL(drm_modeset_lock_all);
129
130/**
131 * drm_modeset_unlock_all - drop all modeset locks
132 * @dev: DRM device
133 *
134 * This function drops all modeset locks taken by a previous call to the
135 * drm_modeset_lock_all() function.
136 *
137 * This function is deprecated. It uses the lock acquisition context stored
138 * in &drm_device.mode_config. This facilitates conversion of existing
139 * code because it removes the need to manually deal with the acquisition
140 * context, but it is also brittle because the context is global and care must
141 * be taken not to nest calls. New code should pass the acquisition context
142 * directly to the drm_modeset_drop_locks() function.
143 */
144void drm_modeset_unlock_all(struct drm_device *dev)
145{
146	struct drm_mode_config *config = &dev->mode_config;
147	struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
148
149	if (WARN_ON(!ctx))
150		return;
151
152	config->acquire_ctx = NULL;
153	drm_modeset_drop_locks(ctx);
154	drm_modeset_acquire_fini(ctx);
155
156	kfree(ctx);
157
158	mutex_unlock(&dev->mode_config.mutex);
159}
160EXPORT_SYMBOL(drm_modeset_unlock_all);
161
162/**
163 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
164 * @dev: device
165 *
166 * Useful as a debug assert.
167 */
168void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
169{
170	struct drm_crtc *crtc;
171
172	/* Locking is currently fubar in the panic handler. */
173	if (oops_in_progress)
174		return;
175
176	drm_for_each_crtc(crtc, dev)
177		WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
178
179	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
180	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
181}
182EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
183
184/**
185 * drm_modeset_acquire_init - initialize acquire context
186 * @ctx: the acquire context
187 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
188 *
189 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
190 * all calls to drm_modeset_lock() will perform an interruptible
191 * wait.
192 */
193void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
194		uint32_t flags)
195{
196	memset(ctx, 0, sizeof(*ctx));
197	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
198	INIT_LIST_HEAD(&ctx->locked);
199
200	if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
201		ctx->interruptible = true;
202}
203EXPORT_SYMBOL(drm_modeset_acquire_init);
204
205/**
206 * drm_modeset_acquire_fini - cleanup acquire context
207 * @ctx: the acquire context
208 */
209void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
210{
211	ww_acquire_fini(&ctx->ww_ctx);
212}
213EXPORT_SYMBOL(drm_modeset_acquire_fini);
214
215/**
216 * drm_modeset_drop_locks - drop all locks
217 * @ctx: the acquire context
218 *
219 * Drop all locks currently held against this acquire context.
220 */
221void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
222{
223	WARN_ON(ctx->contended);
224	while (!list_empty(&ctx->locked)) {
225		struct drm_modeset_lock *lock;
226
227		lock = list_first_entry(&ctx->locked,
228				struct drm_modeset_lock, head);
229
230		drm_modeset_unlock(lock);
231	}
232}
233EXPORT_SYMBOL(drm_modeset_drop_locks);
234
235static inline int modeset_lock(struct drm_modeset_lock *lock,
236		struct drm_modeset_acquire_ctx *ctx,
237		bool interruptible, bool slow)
238{
239	int ret;
240
241	WARN_ON(ctx->contended);
242
243	if (ctx->trylock_only) {
244		lockdep_assert_held(&ctx->ww_ctx);
245
246		if (!ww_mutex_trylock(&lock->mutex))
247			return -EBUSY;
248		else
249			return 0;
250	} else if (interruptible && slow) {
251		ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
252	} else if (interruptible) {
253		ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
254	} else if (slow) {
255		ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
256		ret = 0;
257	} else {
258		ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
259	}
260	if (!ret) {
261		WARN_ON(!list_empty(&lock->head));
262		list_add(&lock->head, &ctx->locked);
263	} else if (ret == -EALREADY) {
264		/* we already hold the lock.. this is fine.  For atomic
265		 * we will need to be able to drm_modeset_lock() things
266		 * without having to keep track of what is already locked
267		 * or not.
268		 */
269		ret = 0;
270	} else if (ret == -EDEADLK) {
271		ctx->contended = lock;
272	}
273
274	return ret;
275}
276
277/**
278 * drm_modeset_backoff - deadlock avoidance backoff
279 * @ctx: the acquire context
280 *
281 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
282 * you must call this function to drop all currently held locks and
283 * block until the contended lock becomes available.
284 *
285 * This function returns 0 on success, or -ERESTARTSYS if this context
286 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
287 * wait has been interrupted.
288 */
289int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
290{
291	struct drm_modeset_lock *contended = ctx->contended;
292
293	ctx->contended = NULL;
294
295	if (WARN_ON(!contended))
296		return 0;
297
298	drm_modeset_drop_locks(ctx);
299
300	return modeset_lock(contended, ctx, ctx->interruptible, true);
301}
302EXPORT_SYMBOL(drm_modeset_backoff);
303
304/**
305 * drm_modeset_lock_init - initialize lock
306 * @lock: lock to init
307 */
308void drm_modeset_lock_init(struct drm_modeset_lock *lock)
309{
310	ww_mutex_init(&lock->mutex, &crtc_ww_class);
311	INIT_LIST_HEAD(&lock->head);
312}
313EXPORT_SYMBOL(drm_modeset_lock_init);
314
315/**
316 * drm_modeset_lock - take modeset lock
317 * @lock: lock to take
318 * @ctx: acquire ctx
319 *
320 * If @ctx is not NULL, then its ww acquire context is used and the
321 * lock will be tracked by the context and can be released by calling
322 * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
323 * deadlock scenario has been detected and it is an error to attempt
324 * to take any more locks without first calling drm_modeset_backoff().
325 *
326 * If the @ctx is not NULL and initialized with
327 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
328 * -ERESTARTSYS when interrupted.
329 *
330 * If @ctx is NULL then the function call behaves like a normal,
331 * uninterruptible non-nesting mutex_lock() call.
332 */
333int drm_modeset_lock(struct drm_modeset_lock *lock,
334		struct drm_modeset_acquire_ctx *ctx)
335{
336	if (ctx)
337		return modeset_lock(lock, ctx, ctx->interruptible, false);
338
339	ww_mutex_lock(&lock->mutex, NULL);
340	return 0;
341}
342EXPORT_SYMBOL(drm_modeset_lock);
343
344/**
345 * drm_modeset_lock_single_interruptible - take a single modeset lock
346 * @lock: lock to take
347 *
348 * This function behaves as drm_modeset_lock() with a NULL context,
349 * but performs interruptible waits.
350 *
351 * This function returns 0 on success, or -ERESTARTSYS when interrupted.
352 */
353int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
354{
355	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
356}
357EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
358
359/**
360 * drm_modeset_unlock - drop modeset lock
361 * @lock: lock to release
362 */
363void drm_modeset_unlock(struct drm_modeset_lock *lock)
364{
365	list_del_init(&lock->head);
366	ww_mutex_unlock(&lock->mutex);
367}
368EXPORT_SYMBOL(drm_modeset_unlock);
369
370/**
371 * drm_modeset_lock_all_ctx - take all modeset locks
372 * @dev: DRM device
373 * @ctx: lock acquisition context
374 *
375 * This function takes all modeset locks, suitable where a more fine-grained
376 * scheme isn't (yet) implemented.
377 *
378 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
379 * since that lock isn't required for modeset state changes. Callers which
380 * need to grab that lock too need to do so outside of the acquire context
381 * @ctx.
382 *
383 * Locks acquired with this function should be released by calling the
384 * drm_modeset_drop_locks() function on @ctx.
385 *
386 * Returns: 0 on success or a negative error-code on failure.
387 */
388int drm_modeset_lock_all_ctx(struct drm_device *dev,
389			     struct drm_modeset_acquire_ctx *ctx)
390{
391	struct drm_crtc *crtc;
392	struct drm_plane *plane;
393	int ret;
394
395	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
396	if (ret)
397		return ret;
398
399	drm_for_each_crtc(crtc, dev) {
400		ret = drm_modeset_lock(&crtc->mutex, ctx);
401		if (ret)
402			return ret;
403	}
404
405	drm_for_each_plane(plane, dev) {
406		ret = drm_modeset_lock(&plane->mutex, ctx);
407		if (ret)
408			return ret;
409	}
410
411	return 0;
412}
413EXPORT_SYMBOL(drm_modeset_lock_all_ctx);