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/drm_atomic.h>
25 #include <drm/drm_crtc.h>
26 #include <drm/drm_device.h>
27 #include <drm/drm_modeset_lock.h>
28
29 /**
30 * DOC: kms locking
31 *
32 * As KMS moves toward more fine grained locking, and atomic ioctl where
33 * userspace can indirectly control locking order, it becomes necessary
34 * to use &ww_mutex and acquire-contexts to avoid deadlocks. But because
35 * the locking is more distributed around the driver code, we want a bit
36 * of extra utility/tracking out of our acquire-ctx. This is provided
37 * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx.
38 *
39 * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.rst
40 *
41 * The basic usage pattern is to::
42 *
43 * drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
44 * retry:
45 * foreach (lock in random_ordered_set_of_locks) {
46 * ret = drm_modeset_lock(lock, ctx)
47 * if (ret == -EDEADLK) {
48 * ret = drm_modeset_backoff(ctx);
49 * if (!ret)
50 * goto retry;
51 * }
52 * if (ret)
53 * goto out;
54 * }
55 * ... do stuff ...
56 * out:
57 * drm_modeset_drop_locks(ctx);
58 * drm_modeset_acquire_fini(ctx);
59 *
60 * For convenience this control flow is implemented in
61 * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
62 * where all modeset locks need to be taken through drm_modeset_lock_all_ctx().
63 *
64 * If all that is needed is a single modeset lock, then the &struct
65 * drm_modeset_acquire_ctx is not needed and the locking can be simplified
66 * by passing a NULL instead of ctx in the drm_modeset_lock() call or
67 * calling drm_modeset_lock_single_interruptible(). To unlock afterwards
68 * call drm_modeset_unlock().
69 *
70 * On top of these per-object locks using &ww_mutex there's also an overall
71 * &drm_mode_config.mutex, for protecting everything else. Mostly this means
72 * probe state of connectors, and preventing hotplug add/removal of connectors.
73 *
74 * Finally there's a bunch of dedicated locks to protect drm core internal
75 * lists and lookup data structures.
76 */
77
78 static DEFINE_WW_CLASS(crtc_ww_class);
79
80 /**
81 * drm_modeset_lock_all - take all modeset locks
82 * @dev: DRM device
83 *
84 * This function takes all modeset locks, suitable where a more fine-grained
85 * scheme isn't (yet) implemented. Locks must be dropped by calling the
86 * drm_modeset_unlock_all() function.
87 *
88 * This function is deprecated. It allocates a lock acquisition context and
89 * stores it in &drm_device.mode_config. This facilitate conversion of
90 * existing code because it removes the need to manually deal with the
91 * acquisition context, but it is also brittle because the context is global
92 * and care must be taken not to nest calls. New code should use the
93 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
94 */
95 void drm_modeset_lock_all(struct drm_device *dev)
96 {
97 struct drm_mode_config *config = &dev->mode_config;
98 struct drm_modeset_acquire_ctx *ctx;
99 int ret;
100
101 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
102 if (WARN_ON(!ctx))
103 return;
104
105 mutex_lock(&config->mutex);
106
107 drm_modeset_acquire_init(ctx, 0);
108
109 retry:
110 ret = drm_modeset_lock_all_ctx(dev, ctx);
111 if (ret < 0) {
112 if (ret == -EDEADLK) {
113 drm_modeset_backoff(ctx);
114 goto retry;
115 }
116
117 drm_modeset_acquire_fini(ctx);
118 kfree(ctx);
119 return;
120 }
121 ww_acquire_done(&ctx->ww_ctx);
122
123 WARN_ON(config->acquire_ctx);
124
125 /*
126 * We hold the locks now, so it is safe to stash the acquisition
127 * context for drm_modeset_unlock_all().
128 */
129 config->acquire_ctx = ctx;
130
131 drm_warn_on_modeset_not_all_locked(dev);
132 }
133 EXPORT_SYMBOL(drm_modeset_lock_all);
134
135 /**
136 * drm_modeset_unlock_all - drop all modeset locks
137 * @dev: DRM device
138 *
139 * This function drops all modeset locks taken by a previous call to the
140 * drm_modeset_lock_all() function.
141 *
142 * This function is deprecated. It uses the lock acquisition context stored
143 * in &drm_device.mode_config. This facilitates conversion of existing
144 * code because it removes the need to manually deal with the acquisition
145 * context, but it is also brittle because the context is global and care must
146 * be taken not to nest calls. New code should pass the acquisition context
147 * directly to the drm_modeset_drop_locks() function.
148 */
149 void drm_modeset_unlock_all(struct drm_device *dev)
150 {
151 struct drm_mode_config *config = &dev->mode_config;
152 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
153
154 if (WARN_ON(!ctx))
155 return;
156
157 config->acquire_ctx = NULL;
158 drm_modeset_drop_locks(ctx);
159 drm_modeset_acquire_fini(ctx);
160
161 kfree(ctx);
162
163 mutex_unlock(&dev->mode_config.mutex);
164 }
165 EXPORT_SYMBOL(drm_modeset_unlock_all);
166
167 /**
168 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
169 * @dev: device
170 *
171 * Useful as a debug assert.
172 */
173 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
174 {
175 struct drm_crtc *crtc;
176
177 /* Locking is currently fubar in the panic handler. */
178 if (oops_in_progress)
179 return;
180
181 drm_for_each_crtc(crtc, dev)
182 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
183
184 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
185 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
186 }
187 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
188
189 /**
190 * drm_modeset_acquire_init - initialize acquire context
191 * @ctx: the acquire context
192 * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
193 *
194 * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
195 * all calls to drm_modeset_lock() will perform an interruptible
196 * wait.
197 */
198 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
199 uint32_t flags)
200 {
201 memset(ctx, 0, sizeof(*ctx));
202 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
203 INIT_LIST_HEAD(&ctx->locked);
204
205 if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
206 ctx->interruptible = true;
207 }
208 EXPORT_SYMBOL(drm_modeset_acquire_init);
209
210 /**
211 * drm_modeset_acquire_fini - cleanup acquire context
212 * @ctx: the acquire context
213 */
214 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
215 {
216 ww_acquire_fini(&ctx->ww_ctx);
217 }
218 EXPORT_SYMBOL(drm_modeset_acquire_fini);
219
220 /**
221 * drm_modeset_drop_locks - drop all locks
222 * @ctx: the acquire context
223 *
224 * Drop all locks currently held against this acquire context.
225 */
226 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
227 {
228 WARN_ON(ctx->contended);
229 while (!list_empty(&ctx->locked)) {
230 struct drm_modeset_lock *lock;
231
232 lock = list_first_entry(&ctx->locked,
233 struct drm_modeset_lock, head);
234
235 drm_modeset_unlock(lock);
236 }
237 }
238 EXPORT_SYMBOL(drm_modeset_drop_locks);
239
240 static inline int modeset_lock(struct drm_modeset_lock *lock,
241 struct drm_modeset_acquire_ctx *ctx,
242 bool interruptible, bool slow)
243 {
244 int ret;
245
246 WARN_ON(ctx->contended);
247
248 if (ctx->trylock_only) {
249 lockdep_assert_held(&ctx->ww_ctx);
250
251 if (!ww_mutex_trylock(&lock->mutex))
252 return -EBUSY;
253 else
254 return 0;
255 } else if (interruptible && slow) {
256 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
257 } else if (interruptible) {
258 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
259 } else if (slow) {
260 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
261 ret = 0;
262 } else {
263 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
264 }
265 if (!ret) {
266 WARN_ON(!list_empty(&lock->head));
267 list_add(&lock->head, &ctx->locked);
268 } else if (ret == -EALREADY) {
269 /* we already hold the lock.. this is fine. For atomic
270 * we will need to be able to drm_modeset_lock() things
271 * without having to keep track of what is already locked
272 * or not.
273 */
274 ret = 0;
275 } else if (ret == -EDEADLK) {
276 ctx->contended = lock;
277 }
278
279 return ret;
280 }
281
282 /**
283 * drm_modeset_backoff - deadlock avoidance backoff
284 * @ctx: the acquire context
285 *
286 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
287 * you must call this function to drop all currently held locks and
288 * block until the contended lock becomes available.
289 *
290 * This function returns 0 on success, or -ERESTARTSYS if this context
291 * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
292 * wait has been interrupted.
293 */
294 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
295 {
296 struct drm_modeset_lock *contended = ctx->contended;
297
298 ctx->contended = NULL;
299
300 if (WARN_ON(!contended))
301 return 0;
302
303 drm_modeset_drop_locks(ctx);
304
305 return modeset_lock(contended, ctx, ctx->interruptible, true);
306 }
307 EXPORT_SYMBOL(drm_modeset_backoff);
308
309 /**
310 * drm_modeset_lock_init - initialize lock
311 * @lock: lock to init
312 */
313 void drm_modeset_lock_init(struct drm_modeset_lock *lock)
314 {
315 ww_mutex_init(&lock->mutex, &crtc_ww_class);
316 INIT_LIST_HEAD(&lock->head);
317 }
318 EXPORT_SYMBOL(drm_modeset_lock_init);
319
320 /**
321 * drm_modeset_lock - take modeset lock
322 * @lock: lock to take
323 * @ctx: acquire ctx
324 *
325 * If @ctx is not NULL, then its ww acquire context is used and the
326 * lock will be tracked by the context and can be released by calling
327 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
328 * deadlock scenario has been detected and it is an error to attempt
329 * to take any more locks without first calling drm_modeset_backoff().
330 *
331 * If the @ctx is not NULL and initialized with
332 * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
333 * -ERESTARTSYS when interrupted.
334 *
335 * If @ctx is NULL then the function call behaves like a normal,
336 * uninterruptible non-nesting mutex_lock() call.
337 */
338 int drm_modeset_lock(struct drm_modeset_lock *lock,
339 struct drm_modeset_acquire_ctx *ctx)
340 {
341 if (ctx)
342 return modeset_lock(lock, ctx, ctx->interruptible, false);
343
344 ww_mutex_lock(&lock->mutex, NULL);
345 return 0;
346 }
347 EXPORT_SYMBOL(drm_modeset_lock);
348
349 /**
350 * drm_modeset_lock_single_interruptible - take a single modeset lock
351 * @lock: lock to take
352 *
353 * This function behaves as drm_modeset_lock() with a NULL context,
354 * but performs interruptible waits.
355 *
356 * This function returns 0 on success, or -ERESTARTSYS when interrupted.
357 */
358 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
359 {
360 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
361 }
362 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
363
364 /**
365 * drm_modeset_unlock - drop modeset lock
366 * @lock: lock to release
367 */
368 void drm_modeset_unlock(struct drm_modeset_lock *lock)
369 {
370 list_del_init(&lock->head);
371 ww_mutex_unlock(&lock->mutex);
372 }
373 EXPORT_SYMBOL(drm_modeset_unlock);
374
375 /**
376 * drm_modeset_lock_all_ctx - take all modeset locks
377 * @dev: DRM device
378 * @ctx: lock acquisition context
379 *
380 * This function takes all modeset locks, suitable where a more fine-grained
381 * scheme isn't (yet) implemented.
382 *
383 * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
384 * since that lock isn't required for modeset state changes. Callers which
385 * need to grab that lock too need to do so outside of the acquire context
386 * @ctx.
387 *
388 * Locks acquired with this function should be released by calling the
389 * drm_modeset_drop_locks() function on @ctx.
390 *
391 * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
392 *
393 * Returns: 0 on success or a negative error-code on failure.
394 */
395 int drm_modeset_lock_all_ctx(struct drm_device *dev,
396 struct drm_modeset_acquire_ctx *ctx)
397 {
398 struct drm_private_obj *privobj;
399 struct drm_crtc *crtc;
400 struct drm_plane *plane;
401 int ret;
402
403 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
404 if (ret)
405 return ret;
406
407 drm_for_each_crtc(crtc, dev) {
408 ret = drm_modeset_lock(&crtc->mutex, ctx);
409 if (ret)
410 return ret;
411 }
412
413 drm_for_each_plane(plane, dev) {
414 ret = drm_modeset_lock(&plane->mutex, ctx);
415 if (ret)
416 return ret;
417 }
418
419 drm_for_each_privobj(privobj, dev) {
420 ret = drm_modeset_lock(&privobj->lock, ctx);
421 if (ret)
422 return ret;
423 }
424
425 return 0;
426 }
427 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);